Parsing changes for recursive pattern-matching (#22718)

src/Compilers/CSharp/Portable/Binder/Binder_Patterns.cs

@@ -54,6 +54,12 @@ private BoundExpression BindIsPatternExpression(IsPatternExpressionSyntax node,
                     return BindConstantPattern(
                         (ConstantPatternSyntax)node, operandType, hasErrors, diagnostics, wasSwitchCase);
 
+                case SyntaxKind.DeconstructionPattern:
+                case SyntaxKind.PropertyPattern:
+                    // PROTOTYPE(patterns2): binding not yet supported for recursive pattern forms.
+                    diagnostics.Add(ErrorCode.ERR_BindToBogus, node.Location, "recursive pattern");
+                    return new BoundConstantPattern(node, BadExpression(node), ConstantValue.Null, hasErrors: true);
+
                 default:
                     throw ExceptionUtilities.UnexpectedValue(node.Kind());
             }

src/Compilers/CSharp/Portable/CSharpResources.Designer.cs

@@ -6415,6 +6415,15 @@ internal class CSharpResources {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Pattern missing.
+        /// </summary>
+        internal static string ERR_MissingPattern {
+            get {
+                return ResourceManager.GetString("ERR_MissingPattern", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Quoted file name, single-line comment or end-of-line expected.
         /// </summary>
@@ -10628,6 +10637,15 @@ internal class CSharpResources {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to recursive patterns.
+        /// </summary>
+        internal static string IDS_FeatureRecursivePatterns {
+            get {
+                return ResourceManager.GetString("IDS_FeatureRecursivePatterns", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to ref extension methods.
         /// </summary>

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -5210,4 +5210,10 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="ERR_RefExtensionMustBeValueTypeOrConstrainedToOne" xml:space="preserve">
     <value>The first parameter of a 'ref' extension method '{0}' must be a value type or a generic type constrained to struct.</value>
   </data>
+  <data name="ERR_MissingPattern" xml:space="preserve">
+    <value>Pattern missing</value>
+  </data>
+  <data name="IDS_FeatureRecursivePatterns" xml:space="preserve">
+    <value>recursive patterns</value>
+  </data>
 </root>
\ No newline at end of file

src/Compilers/CSharp/Portable/Errors/ErrorCode.cs

@@ -1537,5 +1537,11 @@ internal enum ErrorCode
         ERR_EscapeStackAlloc = 8353,
         ERR_RefReturnThis = 8354,
         #endregion diagnostics introduced for `ref readonly`, `ref ternary` and `ref-like` features in C# 7.2
+
+        #region diagnostics introduced for recursive patterns
+        // PROTOTYPE(patterns2): renumber these before committing
+        ERR_MissingPattern = 8500,
+        #endregion diagnostics introduced for recursive patterns
+
     }
 }

src/Compilers/CSharp/Portable/Errors/MessageID.cs

@@ -145,6 +145,8 @@ internal enum MessageID
         IDS_FeatureRefExtensionMethods = MessageBase + 12728,
         IDS_StackAllocExpression = MessageBase + 12729,
         IDS_FeaturePrivateProtected = MessageBase + 12730,
+
+        IDS_FeatureRecursivePatterns = MessageBase + 12731,
     }
 
     // Message IDs may refer to strings that need to be localized.
@@ -190,6 +192,8 @@ internal static string RequiredFeature(this MessageID feature)
             {
                 case MessageID.IDS_FeatureIOperation:
                     return "IOperation";
+                case MessageID.IDS_FeatureRecursivePatterns:
+                    return "patterns2";
                 default:
                     return null;
             }
@@ -197,6 +201,7 @@ internal static string RequiredFeature(this MessageID feature)
 
         internal static LanguageVersion RequiredVersion(this MessageID feature)
         {
+            Debug.Assert(RequiredFeature(feature) == null);
             // Based on CSourceParser::GetFeatureUsage from SourceParser.cpp.
             // Checks are in the LanguageParser unless otherwise noted.
             switch (feature)

src/Compilers/CSharp/Portable/Generated/Syntax.xml.Main.Generated.cs

@@ -460,6 +460,30 @@ public virtual TResult VisitDeclarationPattern(DeclarationPatternSyntax node)
       return this.DefaultVisit(node);
     }
 
+    /// <summary>Called when the visitor visits a DeconstructionPatternSyntax node.</summary>
+    public virtual TResult VisitDeconstructionPattern(DeconstructionPatternSyntax node)
+    {
+      return this.DefaultVisit(node);
+    }
+
+    /// <summary>Called when the visitor visits a SubpatternElementSyntax node.</summary>
+    public virtual TResult VisitSubpatternElement(SubpatternElementSyntax node)
+    {
+      return this.DefaultVisit(node);
+    }
+
+    /// <summary>Called when the visitor visits a PropertyPatternSyntax node.</summary>
+    public virtual TResult VisitPropertyPattern(PropertyPatternSyntax node)
+    {
+      return this.DefaultVisit(node);
+    }
+
+    /// <summary>Called when the visitor visits a PropertySubpatternSyntax node.</summary>
+    public virtual TResult VisitPropertySubpattern(PropertySubpatternSyntax node)
+    {
+      return this.DefaultVisit(node);
+    }
+
     /// <summary>Called when the visitor visits a ConstantPatternSyntax node.</summary>
     public virtual TResult VisitConstantPattern(ConstantPatternSyntax node)
     {
@@ -1687,6 +1711,30 @@ public virtual void VisitDeclarationPattern(DeclarationPatternSyntax node)
       this.DefaultVisit(node);
     }
 
+    /// <summary>Called when the visitor visits a DeconstructionPatternSyntax node.</summary>
+    public virtual void VisitDeconstructionPattern(DeconstructionPatternSyntax node)
+    {
+      this.DefaultVisit(node);
+    }
+
+    /// <summary>Called when the visitor visits a SubpatternElementSyntax node.</summary>
+    public virtual void VisitSubpatternElement(SubpatternElementSyntax node)
+    {
+      this.DefaultVisit(node);
+    }
+
+    /// <summary>Called when the visitor visits a PropertyPatternSyntax node.</summary>
+    public virtual void VisitPropertyPattern(PropertyPatternSyntax node)
+    {
+      this.DefaultVisit(node);
+    }
+
+    /// <summary>Called when the visitor visits a PropertySubpatternSyntax node.</summary>
+    public virtual void VisitPropertySubpattern(PropertySubpatternSyntax node)
+    {
+      this.DefaultVisit(node);
+    }
+
     /// <summary>Called when the visitor visits a ConstantPatternSyntax node.</summary>
     public virtual void VisitConstantPattern(ConstantPatternSyntax node)
     {
@@ -3049,6 +3097,40 @@ public override SyntaxNode VisitDeclarationPattern(DeclarationPatternSyntax node
       return node.Update(type, designation);
     }
 
+    public override SyntaxNode VisitDeconstructionPattern(DeconstructionPatternSyntax node)
+    {
+      var type = (TypeSyntax)this.Visit(node.Type);
+      var openParenToken = this.VisitToken(node.OpenParenToken);
+      var subPatterns = this.VisitList(node.SubPatterns);
+      var closeParenToken = this.VisitToken(node.CloseParenToken);
+      var propertySubpattern = (PropertySubpatternSyntax)this.Visit(node.PropertySubpattern);
+      var designation = (VariableDesignationSyntax)this.Visit(node.Designation);
+      return node.Update(type, openParenToken, subPatterns, closeParenToken, propertySubpattern, designation);
+    }
+
+    public override SyntaxNode VisitSubpatternElement(SubpatternElementSyntax node)
+    {
+      var nameColon = (NameColonSyntax)this.Visit(node.NameColon);
+      var pattern = (PatternSyntax)this.Visit(node.Pattern);
+      return node.Update(nameColon, pattern);
+    }
+
+    public override SyntaxNode VisitPropertyPattern(PropertyPatternSyntax node)
+    {
+      var type = (TypeSyntax)this.Visit(node.Type);
+      var propertySubpattern = (PropertySubpatternSyntax)this.Visit(node.PropertySubpattern);
+      var designation = (VariableDesignationSyntax)this.Visit(node.Designation);
+      return node.Update(type, propertySubpattern, designation);
+    }
+
+    public override SyntaxNode VisitPropertySubpattern(PropertySubpatternSyntax node)
+    {
+      var openBraceToken = this.VisitToken(node.OpenBraceToken);
+      var subPatterns = this.VisitList(node.SubPatterns);
+      var closeBraceToken = this.VisitToken(node.CloseBraceToken);
+      return node.Update(openBraceToken, subPatterns, closeBraceToken);
+    }
+
     public override SyntaxNode VisitConstantPattern(ConstantPatternSyntax node)
     {
       var expression = (ExpressionSyntax)this.Visit(node.Expression);
@@ -6538,6 +6620,96 @@ public static DeclarationPatternSyntax DeclarationPattern(TypeSyntax type, Varia
     }
 
 
+    /// <summary>Creates a new DeconstructionPatternSyntax instance.</summary>
+    public static DeconstructionPatternSyntax DeconstructionPattern(TypeSyntax type, SyntaxToken openParenToken, SeparatedSyntaxList<SubpatternElementSyntax> subPatterns, SyntaxToken closeParenToken, PropertySubpatternSyntax propertySubpattern, VariableDesignationSyntax designation)
+    {
+      switch (openParenToken.Kind())
+      {
+        case SyntaxKind.OpenParenToken:
+          break;
+        default:
+          throw new ArgumentException("openParenToken");
+      }
+      switch (closeParenToken.Kind())
+      {
+        case SyntaxKind.CloseParenToken:
+          break;
+        default:
+          throw new ArgumentException("closeParenToken");
+      }
+      return (DeconstructionPatternSyntax)Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.SyntaxFactory.DeconstructionPattern(type == null ? null : (Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.TypeSyntax)type.Green, (Syntax.InternalSyntax.SyntaxToken)openParenToken.Node, subPatterns.Node.ToGreenSeparatedList<Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.SubpatternElementSyntax>(), (Syntax.InternalSyntax.SyntaxToken)closeParenToken.Node, propertySubpattern == null ? null : (Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.PropertySubpatternSyntax)propertySubpattern.Green, designation == null ? null : (Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.VariableDesignationSyntax)designation.Green).CreateRed();
+    }
+
+
+    /// <summary>Creates a new DeconstructionPatternSyntax instance.</summary>
+    public static DeconstructionPatternSyntax DeconstructionPattern(TypeSyntax type, SeparatedSyntaxList<SubpatternElementSyntax> subPatterns, PropertySubpatternSyntax propertySubpattern, VariableDesignationSyntax designation)
+    {
+      return SyntaxFactory.DeconstructionPattern(type, SyntaxFactory.Token(SyntaxKind.OpenParenToken), subPatterns, SyntaxFactory.Token(SyntaxKind.CloseParenToken), propertySubpattern, designation);
+    }
+
+    /// <summary>Creates a new DeconstructionPatternSyntax instance.</summary>
+    public static DeconstructionPatternSyntax DeconstructionPattern(SeparatedSyntaxList<SubpatternElementSyntax> subPatterns = default(SeparatedSyntaxList<SubpatternElementSyntax>))
+    {
+      return SyntaxFactory.DeconstructionPattern(default(TypeSyntax), SyntaxFactory.Token(SyntaxKind.OpenParenToken), subPatterns, SyntaxFactory.Token(SyntaxKind.CloseParenToken), default(PropertySubpatternSyntax), default(VariableDesignationSyntax));
+    }
+
+    /// <summary>Creates a new SubpatternElementSyntax instance.</summary>
+    public static SubpatternElementSyntax SubpatternElement(NameColonSyntax nameColon, PatternSyntax pattern)
+    {
+      if (pattern == null)
+        throw new ArgumentNullException(nameof(pattern));
+      return (SubpatternElementSyntax)Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.SyntaxFactory.SubpatternElement(nameColon == null ? null : (Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.NameColonSyntax)nameColon.Green, pattern == null ? null : (Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.PatternSyntax)pattern.Green).CreateRed();
+    }
+
+
+    /// <summary>Creates a new SubpatternElementSyntax instance.</summary>
+    public static SubpatternElementSyntax SubpatternElement(PatternSyntax pattern)
+    {
+      return SyntaxFactory.SubpatternElement(default(NameColonSyntax), pattern);
+    }
+
+    /// <summary>Creates a new PropertyPatternSyntax instance.</summary>
+    public static PropertyPatternSyntax PropertyPattern(TypeSyntax type, PropertySubpatternSyntax propertySubpattern, VariableDesignationSyntax designation)
+    {
+      if (propertySubpattern == null)
+        throw new ArgumentNullException(nameof(propertySubpattern));
+      return (PropertyPatternSyntax)Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.SyntaxFactory.PropertyPattern(type == null ? null : (Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.TypeSyntax)type.Green, propertySubpattern == null ? null : (Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.PropertySubpatternSyntax)propertySubpattern.Green, designation == null ? null : (Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.VariableDesignationSyntax)designation.Green).CreateRed();
+    }
+
+
+    /// <summary>Creates a new PropertyPatternSyntax instance.</summary>
+    public static PropertyPatternSyntax PropertyPattern()
+    {
+      return SyntaxFactory.PropertyPattern(default(TypeSyntax), SyntaxFactory.PropertySubpattern(), default(VariableDesignationSyntax));
+    }
+
+    /// <summary>Creates a new PropertySubpatternSyntax instance.</summary>
+    public static PropertySubpatternSyntax PropertySubpattern(SyntaxToken openBraceToken, SeparatedSyntaxList<SubpatternElementSyntax> subPatterns, SyntaxToken closeBraceToken)
+    {
+      switch (openBraceToken.Kind())
+      {
+        case SyntaxKind.OpenBraceToken:
+          break;
+        default:
+          throw new ArgumentException("openBraceToken");
+      }
+      switch (closeBraceToken.Kind())
+      {
+        case SyntaxKind.CloseBraceToken:
+          break;
+        default:
+          throw new ArgumentException("closeBraceToken");
+      }
+      return (PropertySubpatternSyntax)Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.SyntaxFactory.PropertySubpattern((Syntax.InternalSyntax.SyntaxToken)openBraceToken.Node, subPatterns.Node.ToGreenSeparatedList<Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.SubpatternElementSyntax>(), (Syntax.InternalSyntax.SyntaxToken)closeBraceToken.Node).CreateRed();
+    }
+
+
+    /// <summary>Creates a new PropertySubpatternSyntax instance.</summary>
+    public static PropertySubpatternSyntax PropertySubpattern(SeparatedSyntaxList<SubpatternElementSyntax> subPatterns = default(SeparatedSyntaxList<SubpatternElementSyntax>))
+    {
+      return SyntaxFactory.PropertySubpattern(SyntaxFactory.Token(SyntaxKind.OpenBraceToken), subPatterns, SyntaxFactory.Token(SyntaxKind.CloseBraceToken));
+    }
+
     /// <summary>Creates a new ConstantPatternSyntax instance.</summary>
     public static ConstantPatternSyntax ConstantPattern(ExpressionSyntax expression)
     {

src/Compilers/CSharp/Portable/Generated/Syntax.xml.Syntax.Generated.cs

@@ -6791,6 +6791,427 @@ public DeclarationPatternSyntax WithDesignation(VariableDesignationSyntax design
     }
   }
 
+  public sealed partial class DeconstructionPatternSyntax : PatternSyntax
+  {
+    private TypeSyntax type;
+    private SyntaxNode subPatterns;
+    private PropertySubpatternSyntax propertySubpattern;
+    private VariableDesignationSyntax designation;
+
+    internal DeconstructionPatternSyntax(Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.CSharpSyntaxNode green, SyntaxNode parent, int position)
+        : base(green, parent, position)
+    {
+    }
+
+    public TypeSyntax Type 
+    {
+        get
+        {
+            return this.GetRedAtZero(ref this.type);
+        }
+    }
+
+    public SyntaxToken OpenParenToken 
+    {
+      get { return new SyntaxToken(this, ((Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.DeconstructionPatternSyntax)this.Green).openParenToken, this.GetChildPosition(1), this.GetChildIndex(1)); }
+    }
+
+    public SeparatedSyntaxList<SubpatternElementSyntax> SubPatterns 
+    {
+        get
+        {
+            var red = this.GetRed(ref this.subPatterns, 2);
+            if (red != null)
+                return new SeparatedSyntaxList<SubpatternElementSyntax>(red, this.GetChildIndex(2));
+
+            return default(SeparatedSyntaxList<SubpatternElementSyntax>);
+        }
+    }
+
+    public SyntaxToken CloseParenToken 
+    {
+      get { return new SyntaxToken(this, ((Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.DeconstructionPatternSyntax)this.Green).closeParenToken, this.GetChildPosition(3), this.GetChildIndex(3)); }
+    }
+
+    public PropertySubpatternSyntax PropertySubpattern 
+    {
+        get
+        {
+            return this.GetRed(ref this.propertySubpattern, 4);
+        }
+    }
+
+    public VariableDesignationSyntax Designation 
+    {
+        get
+        {
+            return this.GetRed(ref this.designation, 5);
+        }
+    }
+
+    internal override SyntaxNode GetNodeSlot(int index)
+    {
+        switch (index)
+        {
+            case 0: return this.GetRedAtZero(ref this.type);
+            case 2: return this.GetRed(ref this.subPatterns, 2);
+            case 4: return this.GetRed(ref this.propertySubpattern, 4);
+            case 5: return this.GetRed(ref this.designation, 5);
+            default: return null;
+        }
+    }
+    internal override SyntaxNode GetCachedSlot(int index)
+    {
+        switch (index)
+        {
+            case 0: return this.type;
+            case 2: return this.subPatterns;
+            case 4: return this.propertySubpattern;
+            case 5: return this.designation;
+            default: return null;
+        }
+    }
+
+    public override TResult Accept<TResult>(CSharpSyntaxVisitor<TResult> visitor)
+    {
+        return visitor.VisitDeconstructionPattern(this);
+    }
+
+    public override void Accept(CSharpSyntaxVisitor visitor)
+    {
+        visitor.VisitDeconstructionPattern(this);
+    }
+
+    public DeconstructionPatternSyntax Update(TypeSyntax type, SyntaxToken openParenToken, SeparatedSyntaxList<SubpatternElementSyntax> subPatterns, SyntaxToken closeParenToken, PropertySubpatternSyntax propertySubpattern, VariableDesignationSyntax designation)
+    {
+        if (type != this.Type || openParenToken != this.OpenParenToken || subPatterns != this.SubPatterns || closeParenToken != this.CloseParenToken || propertySubpattern != this.PropertySubpattern || designation != this.Designation)
+        {
+            var newNode = SyntaxFactory.DeconstructionPattern(type, openParenToken, subPatterns, closeParenToken, propertySubpattern, designation);
+            var annotations = this.GetAnnotations();
+            if (annotations != null && annotations.Length > 0)
+               return newNode.WithAnnotations(annotations);
+            return newNode;
+        }
+
+        return this;
+    }
+
+    public DeconstructionPatternSyntax WithType(TypeSyntax type)
+    {
+        return this.Update(type, this.OpenParenToken, this.SubPatterns, this.CloseParenToken, this.PropertySubpattern, this.Designation);
+    }
+
+    public DeconstructionPatternSyntax WithOpenParenToken(SyntaxToken openParenToken)
+    {
+        return this.Update(this.Type, openParenToken, this.SubPatterns, this.CloseParenToken, this.PropertySubpattern, this.Designation);
+    }
+
+    public DeconstructionPatternSyntax WithSubPatterns(SeparatedSyntaxList<SubpatternElementSyntax> subPatterns)
+    {
+        return this.Update(this.Type, this.OpenParenToken, subPatterns, this.CloseParenToken, this.PropertySubpattern, this.Designation);
+    }
+
+    public DeconstructionPatternSyntax WithCloseParenToken(SyntaxToken closeParenToken)
+    {
+        return this.Update(this.Type, this.OpenParenToken, this.SubPatterns, closeParenToken, this.PropertySubpattern, this.Designation);
+    }
+
+    public DeconstructionPatternSyntax WithPropertySubpattern(PropertySubpatternSyntax propertySubpattern)
+    {
+        return this.Update(this.Type, this.OpenParenToken, this.SubPatterns, this.CloseParenToken, propertySubpattern, this.Designation);
+    }
+
+    public DeconstructionPatternSyntax WithDesignation(VariableDesignationSyntax designation)
+    {
+        return this.Update(this.Type, this.OpenParenToken, this.SubPatterns, this.CloseParenToken, this.PropertySubpattern, designation);
+    }
+
+    public DeconstructionPatternSyntax AddSubPatterns(params SubpatternElementSyntax[] items)
+    {
+        return this.WithSubPatterns(this.SubPatterns.AddRange(items));
+    }
+
+    public DeconstructionPatternSyntax AddPropertySubpatternSubPatterns(params SubpatternElementSyntax[] items)
+    {
+        var propertySubpattern = this.PropertySubpattern ?? SyntaxFactory.PropertySubpattern();
+        return this.WithPropertySubpattern(propertySubpattern.WithSubPatterns(propertySubpattern.SubPatterns.AddRange(items)));
+    }
+  }
+
+  public sealed partial class SubpatternElementSyntax : CSharpSyntaxNode
+  {
+    private NameColonSyntax nameColon;
+    private PatternSyntax pattern;
+
+    internal SubpatternElementSyntax(Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.CSharpSyntaxNode green, SyntaxNode parent, int position)
+        : base(green, parent, position)
+    {
+    }
+
+    public NameColonSyntax NameColon 
+    {
+        get
+        {
+            return this.GetRedAtZero(ref this.nameColon);
+        }
+    }
+
+    public PatternSyntax Pattern 
+    {
+        get
+        {
+            return this.GetRed(ref this.pattern, 1);
+        }
+    }
+
+    internal override SyntaxNode GetNodeSlot(int index)
+    {
+        switch (index)
+        {
+            case 0: return this.GetRedAtZero(ref this.nameColon);
+            case 1: return this.GetRed(ref this.pattern, 1);
+            default: return null;
+        }
+    }
+    internal override SyntaxNode GetCachedSlot(int index)
+    {
+        switch (index)
+        {
+            case 0: return this.nameColon;
+            case 1: return this.pattern;
+            default: return null;
+        }
+    }
+
+    public override TResult Accept<TResult>(CSharpSyntaxVisitor<TResult> visitor)
+    {
+        return visitor.VisitSubpatternElement(this);
+    }
+
+    public override void Accept(CSharpSyntaxVisitor visitor)
+    {
+        visitor.VisitSubpatternElement(this);
+    }
+
+    public SubpatternElementSyntax Update(NameColonSyntax nameColon, PatternSyntax pattern)
+    {
+        if (nameColon != this.NameColon || pattern != this.Pattern)
+        {
+            var newNode = SyntaxFactory.SubpatternElement(nameColon, pattern);
+            var annotations = this.GetAnnotations();
+            if (annotations != null && annotations.Length > 0)
+               return newNode.WithAnnotations(annotations);
+            return newNode;
+        }
+
+        return this;
+    }
+
+    public SubpatternElementSyntax WithNameColon(NameColonSyntax nameColon)
+    {
+        return this.Update(nameColon, this.Pattern);
+    }
+
+    public SubpatternElementSyntax WithPattern(PatternSyntax pattern)
+    {
+        return this.Update(this.NameColon, pattern);
+    }
+  }
+
+  public sealed partial class PropertyPatternSyntax : PatternSyntax
+  {
+    private TypeSyntax type;
+    private PropertySubpatternSyntax propertySubpattern;
+    private VariableDesignationSyntax designation;
+
+    internal PropertyPatternSyntax(Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.CSharpSyntaxNode green, SyntaxNode parent, int position)
+        : base(green, parent, position)
+    {
+    }
+
+    public TypeSyntax Type 
+    {
+        get
+        {
+            return this.GetRedAtZero(ref this.type);
+        }
+    }
+
+    public PropertySubpatternSyntax PropertySubpattern 
+    {
+        get
+        {
+            return this.GetRed(ref this.propertySubpattern, 1);
+        }
+    }
+
+    public VariableDesignationSyntax Designation 
+    {
+        get
+        {
+            return this.GetRed(ref this.designation, 2);
+        }
+    }
+
+    internal override SyntaxNode GetNodeSlot(int index)
+    {
+        switch (index)
+        {
+            case 0: return this.GetRedAtZero(ref this.type);
+            case 1: return this.GetRed(ref this.propertySubpattern, 1);
+            case 2: return this.GetRed(ref this.designation, 2);
+            default: return null;
+        }
+    }
+    internal override SyntaxNode GetCachedSlot(int index)
+    {
+        switch (index)
+        {
+            case 0: return this.type;
+            case 1: return this.propertySubpattern;
+            case 2: return this.designation;
+            default: return null;
+        }
+    }
+
+    public override TResult Accept<TResult>(CSharpSyntaxVisitor<TResult> visitor)
+    {
+        return visitor.VisitPropertyPattern(this);
+    }
+
+    public override void Accept(CSharpSyntaxVisitor visitor)
+    {
+        visitor.VisitPropertyPattern(this);
+    }
+
+    public PropertyPatternSyntax Update(TypeSyntax type, PropertySubpatternSyntax propertySubpattern, VariableDesignationSyntax designation)
+    {
+        if (type != this.Type || propertySubpattern != this.PropertySubpattern || designation != this.Designation)
+        {
+            var newNode = SyntaxFactory.PropertyPattern(type, propertySubpattern, designation);
+            var annotations = this.GetAnnotations();
+            if (annotations != null && annotations.Length > 0)
+               return newNode.WithAnnotations(annotations);
+            return newNode;
+        }
+
+        return this;
+    }
+
+    public PropertyPatternSyntax WithType(TypeSyntax type)
+    {
+        return this.Update(type, this.PropertySubpattern, this.Designation);
+    }
+
+    public PropertyPatternSyntax WithPropertySubpattern(PropertySubpatternSyntax propertySubpattern)
+    {
+        return this.Update(this.Type, propertySubpattern, this.Designation);
+    }
+
+    public PropertyPatternSyntax WithDesignation(VariableDesignationSyntax designation)
+    {
+        return this.Update(this.Type, this.PropertySubpattern, designation);
+    }
+
+    public PropertyPatternSyntax AddPropertySubpatternSubPatterns(params SubpatternElementSyntax[] items)
+    {
+        return this.WithPropertySubpattern(this.PropertySubpattern.WithSubPatterns(this.PropertySubpattern.SubPatterns.AddRange(items)));
+    }
+  }
+
+  public sealed partial class PropertySubpatternSyntax : CSharpSyntaxNode
+  {
+    private SyntaxNode subPatterns;
+
+    internal PropertySubpatternSyntax(Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.CSharpSyntaxNode green, SyntaxNode parent, int position)
+        : base(green, parent, position)
+    {
+    }
+
+    public SyntaxToken OpenBraceToken 
+    {
+      get { return new SyntaxToken(this, ((Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.PropertySubpatternSyntax)this.Green).openBraceToken, this.Position, 0); }
+    }
+
+    public SeparatedSyntaxList<SubpatternElementSyntax> SubPatterns 
+    {
+        get
+        {
+            var red = this.GetRed(ref this.subPatterns, 1);
+            if (red != null)
+                return new SeparatedSyntaxList<SubpatternElementSyntax>(red, this.GetChildIndex(1));
+
+            return default(SeparatedSyntaxList<SubpatternElementSyntax>);
+        }
+    }
+
+    public SyntaxToken CloseBraceToken 
+    {
+      get { return new SyntaxToken(this, ((Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.PropertySubpatternSyntax)this.Green).closeBraceToken, this.GetChildPosition(2), this.GetChildIndex(2)); }
+    }
+
+    internal override SyntaxNode GetNodeSlot(int index)
+    {
+        switch (index)
+        {
+            case 1: return this.GetRed(ref this.subPatterns, 1);
+            default: return null;
+        }
+    }
+    internal override SyntaxNode GetCachedSlot(int index)
+    {
+        switch (index)
+        {
+            case 1: return this.subPatterns;
+            default: return null;
+        }
+    }
+
+    public override TResult Accept<TResult>(CSharpSyntaxVisitor<TResult> visitor)
+    {
+        return visitor.VisitPropertySubpattern(this);
+    }
+
+    public override void Accept(CSharpSyntaxVisitor visitor)
+    {
+        visitor.VisitPropertySubpattern(this);
+    }
+
+    public PropertySubpatternSyntax Update(SyntaxToken openBraceToken, SeparatedSyntaxList<SubpatternElementSyntax> subPatterns, SyntaxToken closeBraceToken)
+    {
+        if (openBraceToken != this.OpenBraceToken || subPatterns != this.SubPatterns || closeBraceToken != this.CloseBraceToken)
+        {
+            var newNode = SyntaxFactory.PropertySubpattern(openBraceToken, subPatterns, closeBraceToken);
+            var annotations = this.GetAnnotations();
+            if (annotations != null && annotations.Length > 0)
+               return newNode.WithAnnotations(annotations);
+            return newNode;
+        }
+
+        return this;
+    }
+
+    public PropertySubpatternSyntax WithOpenBraceToken(SyntaxToken openBraceToken)
+    {
+        return this.Update(openBraceToken, this.SubPatterns, this.CloseBraceToken);
+    }
+
+    public PropertySubpatternSyntax WithSubPatterns(SeparatedSyntaxList<SubpatternElementSyntax> subPatterns)
+    {
+        return this.Update(this.OpenBraceToken, subPatterns, this.CloseBraceToken);
+    }
+
+    public PropertySubpatternSyntax WithCloseBraceToken(SyntaxToken closeBraceToken)
+    {
+        return this.Update(this.OpenBraceToken, this.SubPatterns, closeBraceToken);
+    }
+
+    public PropertySubpatternSyntax AddSubPatterns(params SubpatternElementSyntax[] items)
+    {
+        return this.WithSubPatterns(this.SubPatterns.AddRange(items));
+    }
+  }
+
   public sealed partial class ConstantPatternSyntax : PatternSyntax
   {
     private ExpressionSyntax expression;

src/Compilers/CSharp/Portable/GlobalSuppressions.cs

@@ -24,4 +24,6 @@
 [assembly: System.Diagnostics.CodeAnalysis.SuppressMessage("ApiDesign", "RS0027:Public API with optional parameter(s) should have the most parameters amongst its public overloads.", Justification = "<Pending>", Scope = "member", Target = "~M:Microsoft.CodeAnalysis.CSharp.SyntaxFactory.ParenthesizedVariableDesignation(Microsoft.CodeAnalysis.SeparatedSyntaxList{Microsoft.CodeAnalysis.CSharp.Syntax.VariableDesignationSyntax})~Microsoft.CodeAnalysis.CSharp.Syntax.ParenthesizedVariableDesignationSyntax")]
 [assembly: System.Diagnostics.CodeAnalysis.SuppressMessage("ApiDesign", "RS0026:Do not add multiple public overloads with optional parameters", Justification = "<Pending>", Scope = "member", Target = "~M:Microsoft.CodeAnalysis.CSharp.CSharpExtensions.GetDeclaredSymbol(Microsoft.CodeAnalysis.SemanticModel,Microsoft.CodeAnalysis.CSharp.Syntax.TupleExpressionSyntax,System.Threading.CancellationToken)~Microsoft.CodeAnalysis.INamedTypeSymbol")]
 [assembly: System.Diagnostics.CodeAnalysis.SuppressMessage("ApiDesign", "RS0026:Do not add multiple public overloads with optional parameters", Justification = "<Pending>", Scope = "member", Target = "~M:Microsoft.CodeAnalysis.CSharp.CSharpExtensions.GetDeclaredSymbol(Microsoft.CodeAnalysis.SemanticModel,Microsoft.CodeAnalysis.CSharp.Syntax.ArgumentSyntax,System.Threading.CancellationToken)~Microsoft.CodeAnalysis.ISymbol")]
+[assembly: System.Diagnostics.CodeAnalysis.SuppressMessage("ApiDesign", "RS0027:Public API with optional parameter(s) should have the most parameters amongst its public overloads.", Justification = "<Pending>", Scope = "member", Target = "~M:Microsoft.CodeAnalysis.CSharp.SyntaxFactory.DeconstructionPattern(Microsoft.CodeAnalysis.SeparatedSyntaxList{Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax})~Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax")]
+[assembly: System.Diagnostics.CodeAnalysis.SuppressMessage("ApiDesign", "RS0027:Public API with optional parameter(s) should have the most parameters amongst its public overloads.", Justification = "<Pending>", Scope = "member", Target = "~M:Microsoft.CodeAnalysis.CSharp.SyntaxFactory.PropertySubpattern(Microsoft.CodeAnalysis.SeparatedSyntaxList{Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax})~Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax")]
 

src/Compilers/CSharp/Portable/Parser/LanguageParser.cs

@@ -4859,7 +4859,7 @@ private enum NameOptions
             InTypeList = 1 << 1, // Allows attributes to appear within the generic type argument list. Used during ParseInstantiation.
             PossiblePattern = 1 << 2, // Used to influence parser ambiguity around "<" and generics vs. expressions on the right of 'is'
             AfterIs = 1 << 3,
-            AfterCase = 1 << 4,
+            DefinitePattern = 1 << 4,
             AfterOut = 1 << 5,
             AfterTupleComma = 1 << 6,
             FirstElementOfPossibleTupleLiteral = 1 << 7,
@@ -5154,7 +5154,7 @@ private ScanTypeArgumentListKind ScanTypeArgumentList(NameOptions options)
                     // subsequent element of a tuple literal (in which case the tokens are preceded by `,` and the
                     // identifier is followed by a `,` or `)`).
                     // Note that we treat query contextual keywords (which appear here as identifiers) as disambiguating tokens as well.
-                    if ((options & (NameOptions.AfterIs | NameOptions.AfterCase | NameOptions.AfterOut)) != 0 ||
+                    if ((options & (NameOptions.AfterIs | NameOptions.DefinitePattern | NameOptions.AfterOut)) != 0 ||
                         (options & NameOptions.AfterTupleComma) != 0 && (this.PeekToken(1).Kind == SyntaxKind.CommaToken || this.PeekToken(1).Kind == SyntaxKind.CloseParenToken) ||
                         (options & NameOptions.FirstElementOfPossibleTupleLiteral) != 0 && this.PeekToken(1).Kind == SyntaxKind.CommaToken
                         )
@@ -5824,15 +5824,15 @@ private bool IsPossibleName()
             return this.IsTrueIdentifier();
         }
 
-        private ScanTypeFlags ScanType()
+        private ScanTypeFlags ScanType(bool forPattern = false)
         {
             SyntaxToken lastTokenOfType;
             return ScanType(out lastTokenOfType);
         }
 
-        private ScanTypeFlags ScanType(out SyntaxToken lastTokenOfType)
+        private ScanTypeFlags ScanType(out SyntaxToken lastTokenOfType, bool forPattern = false)
         {
-            return ScanType(ParseTypeMode.Normal, out lastTokenOfType);
+            return ScanType(forPattern ? ParseTypeMode.DefinitePattern : ParseTypeMode.Normal, out lastTokenOfType);
         }
 
         private ScanTypeFlags ScanType(ParseTypeMode mode, out SyntaxToken lastTokenOfType)
@@ -5950,7 +5950,7 @@ private ScanTypeFlags ScanNonArrayType(ParseTypeMode mode, out SyntaxToken lastT
                 lastTokenOfType = this.EatToken();
                 result = ScanTypeFlags.MustBeType;
             }
-            else if (this.CurrentToken.Kind == SyntaxKind.OpenParenToken)
+            else if (this.CurrentToken.Kind == SyntaxKind.OpenParenToken && mode != ParseTypeMode.DefinitePattern)
             {
                 lastTokenOfType = this.EatToken();
 
@@ -5981,6 +5981,9 @@ private ScanTypeFlags ScanNonArrayType(ParseTypeMode mode, out SyntaxToken lastT
                     // We are parsing the type for a declaration expression in a tuple, which does
                     // not permit pointer types. In that context a `*` is parsed as a multiplication.
                     break;
+                case ParseTypeMode.DefinitePattern:
+                    // pointer type syntax is not supported in patterns.
+                    break;
                 default:
                     while (this.CurrentToken.Kind == SyntaxKind.AsteriskToken)
                     {
@@ -6110,7 +6113,7 @@ private enum ParseTypeMode
             Normal,
             Parameter,
             AfterIs,
-            AfterCase,
+            DefinitePattern,
             AfterOut,
             AfterTupleComma,
             AsExpression,
@@ -6152,8 +6155,8 @@ private enum ParseTypeMode
                 case ParseTypeMode.AfterIs:
                     nameOptions = NameOptions.InExpression | NameOptions.AfterIs | NameOptions.PossiblePattern;
                     break;
-                case ParseTypeMode.AfterCase:
-                    nameOptions = NameOptions.InExpression | NameOptions.AfterCase | NameOptions.PossiblePattern;
+                case ParseTypeMode.DefinitePattern:
+                    nameOptions = NameOptions.InExpression | NameOptions.DefinitePattern | NameOptions.PossiblePattern;
                     break;
                 case ParseTypeMode.AfterOut:
                     nameOptions = NameOptions.InExpression | NameOptions.AfterOut;
@@ -6178,7 +6181,7 @@ private enum ParseTypeMode
 
             if (this.CurrentToken.Kind == SyntaxKind.QuestionToken &&
                 // we do not permit nullable types in a declaration pattern
-                (mode != ParseTypeMode.AfterIs && mode != ParseTypeMode.AfterCase || !IsTrueIdentifier(this.PeekToken(1))))
+                (mode != ParseTypeMode.AfterIs && mode != ParseTypeMode.DefinitePattern || !IsTrueIdentifier(this.PeekToken(1))))
             {
                 var resetPoint = this.GetResetPoint();
                 try
@@ -6206,7 +6209,7 @@ private enum ParseTypeMode
             switch (mode)
             {
                 case ParseTypeMode.AfterIs:
-                case ParseTypeMode.AfterCase:
+                case ParseTypeMode.DefinitePattern:
                 case ParseTypeMode.AfterTupleComma:
                 case ParseTypeMode.FirstElementOfPossibleTupleLiteral:
                     // these contexts do not permit a pointer type.
@@ -7964,7 +7967,7 @@ private SwitchSectionSyntax ParseSwitchSection()
                         }
                         else
                         {
-                            var node = ParseExpressionOrPatternForCase();
+                            var node = ParseExpressionOrPattern(forCase: true);
                             if (this.CurrentToken.ContextualKind == SyntaxKind.WhenKeyword && node is ExpressionSyntax)
                             {
                                 // if there is a 'where' token, we treat a case expression as a constant pattern.
@@ -9444,10 +9447,7 @@ internal ArgumentListSyntax ParseParenthesizedArgumentList()
                 return (ArgumentListSyntax)this.EatNode();
             }
 
-            SyntaxToken openToken, closeToken;
-            SeparatedSyntaxList<ArgumentSyntax> arguments;
-            ParseArgumentList(out openToken, out arguments, out closeToken, SyntaxKind.OpenParenToken, SyntaxKind.CloseParenToken);
-
+            ParseArgumentList(out var openToken, out var arguments, out var closeToken, SyntaxKind.OpenParenToken, SyntaxKind.CloseParenToken);
             return _syntaxFactory.ArgumentList(openToken, arguments, closeToken);
         }
 
@@ -9458,10 +9458,7 @@ internal BracketedArgumentListSyntax ParseBracketedArgumentList()
                 return (BracketedArgumentListSyntax)this.EatNode();
             }
 
-            SyntaxToken openToken, closeToken;
-            SeparatedSyntaxList<ArgumentSyntax> arguments;
-            ParseArgumentList(out openToken, out arguments, out closeToken, SyntaxKind.OpenBracketToken, SyntaxKind.CloseBracketToken);
-
+            ParseArgumentList(out var openToken, out var arguments, out var closeToken, SyntaxKind.OpenBracketToken, SyntaxKind.CloseBracketToken);
             return _syntaxFactory.BracketedArgumentList(openToken, arguments, closeToken);
         }
 
@@ -10006,7 +10003,7 @@ private TupleExpressionSyntax ParseTupleExpressionTail(SyntaxToken openParen, Ar
             }
         }
 
-        private bool ScanCast()
+        private bool ScanCast(bool forPattern = false)
         {
             if (this.CurrentToken.Kind != SyntaxKind.OpenParenToken)
             {
@@ -10015,7 +10012,7 @@ private bool ScanCast()
 
             this.EatToken();
 
-            var type = this.ScanType();
+            var type = this.ScanType(forPattern: forPattern);
             if (type == ScanTypeFlags.NotType)
             {
                 return false;
@@ -10142,6 +10139,7 @@ private static bool CanFollowCast(SyntaxKind kind)
                 case SyntaxKind.MinusGreaterThanToken:
                 case SyntaxKind.QuestionQuestionToken:
                 case SyntaxKind.EndOfFileToken:
+                case SyntaxKind.EqualsGreaterThanToken:
                     return false;
                 default:
                     return true;

src/Compilers/CSharp/Portable/Parser/LanguageParser_Patterns.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-using System;
 using System.Diagnostics;
+using Roslyn.Utilities;
+
 
 namespace Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax
 {
@@ -222,51 +223,242 @@ private bool ScanDesignation(bool permitTuple)
 
         // Priority is the ExpressionSyntax. It might return ExpressionSyntax which might be a constant pattern such as 'case 3:' 
         // All constant expressions are converted to the constant pattern in the switch binder if it is a match statement.
-        // It is used for parsing patterns in the switch cases. It never returns constant pattern!
-        private CSharpSyntaxNode ParseExpressionOrPatternForCase()
+        // It is used for parsing patterns in the switch cases. It never returns constant pattern, because for a `case` we
+        // need to use a pre-pattern-matching syntax node for a constant case.
+        private CSharpSyntaxNode ParseExpressionOrPattern(bool forCase)
         {
-            var tk = this.CurrentToken.Kind;
-            CSharpSyntaxNode node = null;
-
-            // If it is a nameof, skip the 'if' and parse as an expression. 
-            if ((SyntaxFacts.IsPredefinedType(tk) || tk == SyntaxKind.IdentifierToken) &&
-                  this.CurrentToken.ContextualKind != SyntaxKind.NameOfKeyword)
+            // handle common error recovery situations during typing
+            switch (this.CurrentToken.Kind)
             {
+                case SyntaxKind.CommaToken:
+                case SyntaxKind.SemicolonToken:
+                case SyntaxKind.CloseBraceToken:
+                case SyntaxKind.CloseParenToken:
+                case SyntaxKind.CloseBracketToken:
+                case SyntaxKind.EqualsGreaterThanToken:
+                    return this.ParseIdentifierName(ErrorCode.ERR_MissingArgument);
+            }
+
             var resetPoint = this.GetResetPoint();
             try
             {
-                    TypeSyntax type = this.ParseType(ParseTypeMode.AfterCase);
-                    if (!type.IsMissing)
+                TypeSyntax type = null;
+                var tk = this.CurrentToken.Kind;
+                if ((SyntaxFacts.IsPredefinedType(tk) || tk == SyntaxKind.IdentifierToken) &&
+                      // If it is a nameof, skip the 'if' and parse as an expression. 
+                      (this.CurrentToken.ContextualKind != SyntaxKind.NameOfKeyword || this.PeekToken(1).Kind != SyntaxKind.OpenParenToken))
                 {
-                        // X.Y.Z id
-                        if (this.IsTrueIdentifier() && this.CurrentToken.ContextualKind != SyntaxKind.WhenKeyword)
+                    type = this.ParseType(ParseTypeMode.DefinitePattern);
+                    if (type.IsMissing)
                     {
-                            var designation = ParseSimpleDesignation();
-                            node = _syntaxFactory.DeclarationPattern(type, designation);
+                        // either it is not shaped like a type, or it is a constant expression.
+                        this.Reset(ref resetPoint);
+                        type = null;
+                    }
+                }
+
+                PropertySubpatternSyntax propertySubpattern = null;
+                bool parsePropertySubpattern()
+                {
+                    if (this.CurrentToken.Kind == SyntaxKind.OpenBraceToken)
+                    {
+                        propertySubpattern = ParsePropertySubpattern();
+                        return true;
+                    }
+
+                    return false;
                 }
+
+                VariableDesignationSyntax designation = null;
+                bool parseDesignation()
+                {
+                    if (this.IsTrueIdentifier() && (!forCase || this.CurrentToken.ContextualKind != SyntaxKind.WhenKeyword))
+                    {
+                        designation = ParseSimpleDesignation();
+                        return true;
+                    }
+
+                    return false;
                 }
-                    if (node == null)
+
+                bool looksLikeCast()
+                {
+                    var resetPoint2 = this.GetResetPoint();
+                    try
                     {
-                        // it is an expression for typical switch case. 
+                        return this.ScanCast(forPattern: true);
+                    }
+                    finally
+                    {
+                        this.Reset(ref resetPoint2);
+                        this.Release(ref resetPoint2);
+                    }
+                }
+
+                if (this.CurrentToken.Kind == SyntaxKind.OpenParenToken && (type != null || !looksLikeCast()))
+                {
+                    // It is possible this is a parenthesized (constant) expression.
+                    // We normalize later.
+                    ParseSubpatternList(out var openParenToken, out var subPatterns, out var closeParenToken, SyntaxKind.OpenParenToken, SyntaxKind.CloseParenToken);
+                    if (this.CurrentToken.Kind == SyntaxKind.EqualsGreaterThanToken)
+                    {
+                        // Testers do the darndest things, in this case putting a lambda expression where a pattern is expected.
                         this.Reset(ref resetPoint);
-                        node = this.ParseSubExpression(Precedence.Expression);
+                        return this.ParseSubExpression(Precedence.Expression);
                     }
+
+                    parsePropertySubpattern();
+                    parseDesignation();
+
+                    if (type == null &&
+                        propertySubpattern == null &&
+                        designation == null &&
+                        subPatterns.Count == 1 &&
+                        subPatterns[0].NameColon == null &&
+                        subPatterns[0].Pattern is ConstantPatternSyntax cp)
+                    {
+                        // There is an ambiguity between a deconstruction pattern `(` pattern `)`
+                        // and a constant expression pattern than happens to be parenthesized.
+                        // We normalize to the parenthesized expression, and semantic analysis
+                        // will notice the parens and treat it whichever way is semantically sensible,
+                        // giving priority to its treatment as a constant expression.
+                        return _syntaxFactory.ParenthesizedExpression(openParenToken, cp.Expression, closeParenToken);
+                    }
+
+                    var node = _syntaxFactory.DeconstructionPattern(type, openParenToken, subPatterns, closeParenToken, propertySubpattern, designation);
+                    return this.CheckFeatureAvailability(node, MessageID.IDS_FeatureRecursivePatterns);
+                }
+
+                if (parsePropertySubpattern())
+                {
+                    parseDesignation();
+                    var node = _syntaxFactory.PropertyPattern(type, propertySubpattern, designation);
+                    return this.CheckFeatureAvailability(node, MessageID.IDS_FeatureRecursivePatterns);
+                }
+
+                if (type != null && parseDesignation())
+                {
+                    return _syntaxFactory.DeclarationPattern(type, designation);
+                }
+
+                this.Reset(ref resetPoint);
+                return this.ParseSubExpression(Precedence.Expression);
             }
             finally
             {
                 this.Release(ref resetPoint);
             }
         }
-            else
+
+        private PatternSyntax ParsePattern()
         {
-                // In places where a pattern is supported, we do not support tuple types
-                // due to both syntactic and semantic ambiguities between tuple types and positional patterns.
+            var node = ParseExpressionOrPattern(forCase: false);
+            switch (node)
+            {
+                case PatternSyntax pattern:
+                    return pattern;
+                case ExpressionSyntax expression:
+                    return _syntaxFactory.ConstantPattern(expression);
+                default:
+                    throw ExceptionUtilities.UnexpectedValue(node);
+            }
+        }
 
-                // But it still might be a pattern such as (operand is 3) or (operand is nameof(x))
-                node = this.ParseSubExpression(Precedence.Expression);
+        private PropertySubpatternSyntax ParsePropertySubpattern()
+        {
+            ParseSubpatternList(out var openBraceToken, out var subPatterns, out var closeBraceToken, SyntaxKind.OpenBraceToken, SyntaxKind.CloseBraceToken);
+            return _syntaxFactory.PropertySubpattern(openBraceToken, subPatterns, closeBraceToken);
+        }
+
+        private void ParseSubpatternList(
+            out SyntaxToken openToken,
+            out Microsoft.CodeAnalysis.Syntax.InternalSyntax.SeparatedSyntaxList<SubpatternElementSyntax> subPatterns,
+            out SyntaxToken closeToken,
+            SyntaxKind openKind,
+            SyntaxKind closeKind)
+        {
+            Debug.Assert(openKind == SyntaxKind.OpenParenToken || openKind == SyntaxKind.OpenBraceToken);
+            Debug.Assert(closeKind == SyntaxKind.CloseParenToken || closeKind == SyntaxKind.CloseBraceToken);
+            Debug.Assert((openKind == SyntaxKind.OpenParenToken) == (closeKind == SyntaxKind.CloseParenToken));
+
+            openToken = this.EatToken(openKind);
+            var list = _pool.AllocateSeparated<SubpatternElementSyntax>();
+            try
+            {
+                if (this.CurrentToken.Kind != closeKind && this.CurrentToken.Kind != SyntaxKind.SemicolonToken)
+                {
+                    tryAgain:
+
+                    if (this.IsPossibleSubpatternElement() || this.CurrentToken.Kind == SyntaxKind.CommaToken)
+                    {
+                        // first pattern
+                        list.Add(this.ParseSubpatternElement());
+
+                        // additional patterns
+                        while (true)
+                        {
+                            if (this.CurrentToken.Kind == SyntaxKind.CloseParenToken ||
+                                this.CurrentToken.Kind == SyntaxKind.CloseBraceToken ||
+                                this.CurrentToken.Kind == SyntaxKind.SemicolonToken)
+                            {
+                                break;
+                            }
+                            else if (this.CurrentToken.Kind == SyntaxKind.CommaToken || this.IsPossibleSubpatternElement())
+                            {
+                                list.AddSeparator(this.EatToken(SyntaxKind.CommaToken));
+                                list.Add(this.ParseSubpatternElement());
+                                continue;
+                            }
+                            else if (this.SkipBadPatternListTokens(ref openToken, list, SyntaxKind.CommaToken, closeKind) == PostSkipAction.Abort)
+                            {
+                                break;
+                            }
+                        }
+                    }
+                    else if (this.SkipBadPatternListTokens(ref openToken, list, SyntaxKind.IdentifierToken, closeKind) == PostSkipAction.Continue)
+                    {
+                        goto tryAgain;
+                    }
+                }
+
+                closeToken = this.EatToken(closeKind);
+                subPatterns = list.ToList();
+            }
+            finally
+            {
+                _pool.Free(list);
+            }
+        }
+
+        private SubpatternElementSyntax ParseSubpatternElement()
+        {
+            NameColonSyntax nameColon = null;
+            if (this.CurrentToken.Kind == SyntaxKind.IdentifierToken && this.PeekToken(1).Kind == SyntaxKind.ColonToken)
+            {
+                var name = this.ParseIdentifierName();
+                var colon = this.EatToken(SyntaxKind.ColonToken);
+                nameColon = _syntaxFactory.NameColon(name, colon);
+            }
+
+            var pattern = ParsePattern();
+            return this._syntaxFactory.SubpatternElement(nameColon, pattern);
+        }
+
+        private bool IsPossibleSubpatternElement()
+        {
+            return this.IsPossibleExpression() || this.CurrentToken.Kind == SyntaxKind.OpenBraceToken;
         }
 
-            return node;
+        private PostSkipAction SkipBadPatternListTokens(
+            ref SyntaxToken open,
+            Microsoft.CodeAnalysis.Syntax.InternalSyntax.SeparatedSyntaxListBuilder<SubpatternElementSyntax> list,
+            SyntaxKind expected,
+            SyntaxKind closeKind)
+        {
+            return this.SkipBadSeparatedListTokensWithExpectedKind(ref open, list,
+                p => p.CurrentToken.Kind != SyntaxKind.CommaToken && !p.IsPossibleSubpatternElement(),
+                p => p.CurrentToken.Kind == closeKind || p.CurrentToken.Kind == SyntaxKind.SemicolonToken || p.IsTerminator(),
+                expected);
         }
     }
 }

src/Compilers/CSharp/Portable/PublicAPI.Unshipped.txt

+Microsoft.CodeAnalysis.CSharp.Conversion.IsStackAlloc.get -> bool
 Microsoft.CodeAnalysis.CSharp.Conversion.ToCommonConversion() -> Microsoft.CodeAnalysis.Semantics.CommonConversion
 Microsoft.CodeAnalysis.CSharp.LanguageVersion.CSharp7_2 = 702 -> Microsoft.CodeAnalysis.CSharp.LanguageVersion
-static Microsoft.CodeAnalysis.CSharp.CSharpExtensions.GetConversion(this Microsoft.CodeAnalysis.Semantics.IConversionExpression conversionExpression) -> Microsoft.CodeAnalysis.CSharp.Conversion
+Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax.AddPropertySubpatternSubPatterns(params Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax[] items) -> Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax.AddSubPatterns(params Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax[] items) -> Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax.CloseParenToken.get -> Microsoft.CodeAnalysis.SyntaxToken
+Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax.Designation.get -> Microsoft.CodeAnalysis.CSharp.Syntax.VariableDesignationSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax.OpenParenToken.get -> Microsoft.CodeAnalysis.SyntaxToken
+Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax.PropertySubpattern.get -> Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax.SubPatterns.get -> Microsoft.CodeAnalysis.SeparatedSyntaxList<Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax>
+Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax.Type.get -> Microsoft.CodeAnalysis.CSharp.Syntax.TypeSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax.Update(Microsoft.CodeAnalysis.CSharp.Syntax.TypeSyntax type, Microsoft.CodeAnalysis.SyntaxToken openParenToken, Microsoft.CodeAnalysis.SeparatedSyntaxList<Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax> subPatterns, Microsoft.CodeAnalysis.SyntaxToken closeParenToken, Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax propertySubpattern, Microsoft.CodeAnalysis.CSharp.Syntax.VariableDesignationSyntax designation) -> Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax.WithCloseParenToken(Microsoft.CodeAnalysis.SyntaxToken closeParenToken) -> Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax.WithDesignation(Microsoft.CodeAnalysis.CSharp.Syntax.VariableDesignationSyntax designation) -> Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax.WithOpenParenToken(Microsoft.CodeAnalysis.SyntaxToken openParenToken) -> Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax.WithPropertySubpattern(Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax propertySubpattern) -> Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax.WithSubPatterns(Microsoft.CodeAnalysis.SeparatedSyntaxList<Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax> subPatterns) -> Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax.WithType(Microsoft.CodeAnalysis.CSharp.Syntax.TypeSyntax type) -> Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax.AddPropertySubpatternSubPatterns(params Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax[] items) -> Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax.Designation.get -> Microsoft.CodeAnalysis.CSharp.Syntax.VariableDesignationSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax.PropertySubpattern.get -> Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax.Type.get -> Microsoft.CodeAnalysis.CSharp.Syntax.TypeSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax.Update(Microsoft.CodeAnalysis.CSharp.Syntax.TypeSyntax type, Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax propertySubpattern, Microsoft.CodeAnalysis.CSharp.Syntax.VariableDesignationSyntax designation) -> Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax.WithDesignation(Microsoft.CodeAnalysis.CSharp.Syntax.VariableDesignationSyntax designation) -> Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax.WithPropertySubpattern(Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax propertySubpattern) -> Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax.WithType(Microsoft.CodeAnalysis.CSharp.Syntax.TypeSyntax type) -> Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax.AddSubPatterns(params Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax[] items) -> Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax.CloseBraceToken.get -> Microsoft.CodeAnalysis.SyntaxToken
+Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax.OpenBraceToken.get -> Microsoft.CodeAnalysis.SyntaxToken
+Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax.SubPatterns.get -> Microsoft.CodeAnalysis.SeparatedSyntaxList<Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax>
+Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax.Update(Microsoft.CodeAnalysis.SyntaxToken openBraceToken, Microsoft.CodeAnalysis.SeparatedSyntaxList<Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax> subPatterns, Microsoft.CodeAnalysis.SyntaxToken closeBraceToken) -> Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax.WithCloseBraceToken(Microsoft.CodeAnalysis.SyntaxToken closeBraceToken) -> Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax.WithOpenBraceToken(Microsoft.CodeAnalysis.SyntaxToken openBraceToken) -> Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax.WithSubPatterns(Microsoft.CodeAnalysis.SeparatedSyntaxList<Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax> subPatterns) -> Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax
 Microsoft.CodeAnalysis.CSharp.Syntax.RefTypeSyntax.ReadOnlyKeyword.get -> Microsoft.CodeAnalysis.SyntaxToken
 Microsoft.CodeAnalysis.CSharp.Syntax.RefTypeSyntax.Update(Microsoft.CodeAnalysis.SyntaxToken refKeyword, Microsoft.CodeAnalysis.SyntaxToken readOnlyKeyword, Microsoft.CodeAnalysis.CSharp.Syntax.TypeSyntax type) -> Microsoft.CodeAnalysis.CSharp.Syntax.RefTypeSyntax
 Microsoft.CodeAnalysis.CSharp.Syntax.RefTypeSyntax.WithReadOnlyKeyword(Microsoft.CodeAnalysis.SyntaxToken readOnlyKeyword) -> Microsoft.CodeAnalysis.CSharp.Syntax.RefTypeSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax.NameColon.get -> Microsoft.CodeAnalysis.CSharp.Syntax.NameColonSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax.Pattern.get -> Microsoft.CodeAnalysis.CSharp.Syntax.PatternSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax.Update(Microsoft.CodeAnalysis.CSharp.Syntax.NameColonSyntax nameColon, Microsoft.CodeAnalysis.CSharp.Syntax.PatternSyntax pattern) -> Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax.WithNameColon(Microsoft.CodeAnalysis.CSharp.Syntax.NameColonSyntax nameColon) -> Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax
+Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax.WithPattern(Microsoft.CodeAnalysis.CSharp.Syntax.PatternSyntax pattern) -> Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax
+Microsoft.CodeAnalysis.CSharp.SyntaxKind.DeconstructionPattern = 9023 -> Microsoft.CodeAnalysis.CSharp.SyntaxKind
+Microsoft.CodeAnalysis.CSharp.SyntaxKind.PropertyPattern = 9020 -> Microsoft.CodeAnalysis.CSharp.SyntaxKind
+Microsoft.CodeAnalysis.CSharp.SyntaxKind.PropertySubpattern = 9021 -> Microsoft.CodeAnalysis.CSharp.SyntaxKind
+Microsoft.CodeAnalysis.CSharp.SyntaxKind.SubpatternElement = 9022 -> Microsoft.CodeAnalysis.CSharp.SyntaxKind
+override Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.VisitDeconstructionPattern(Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax node) -> Microsoft.CodeAnalysis.SyntaxNode
+override Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.VisitPropertyPattern(Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax node) -> Microsoft.CodeAnalysis.SyntaxNode
+override Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.VisitPropertySubpattern(Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax node) -> Microsoft.CodeAnalysis.SyntaxNode
+override Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.VisitSubpatternElement(Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax node) -> Microsoft.CodeAnalysis.SyntaxNode
+override Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax.Accept(Microsoft.CodeAnalysis.CSharp.CSharpSyntaxVisitor visitor) -> void
+override Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax.Accept<TResult>(Microsoft.CodeAnalysis.CSharp.CSharpSyntaxVisitor<TResult> visitor) -> TResult
+override Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax.Accept(Microsoft.CodeAnalysis.CSharp.CSharpSyntaxVisitor visitor) -> void
+override Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax.Accept<TResult>(Microsoft.CodeAnalysis.CSharp.CSharpSyntaxVisitor<TResult> visitor) -> TResult
+override Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax.Accept(Microsoft.CodeAnalysis.CSharp.CSharpSyntaxVisitor visitor) -> void
+override Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax.Accept<TResult>(Microsoft.CodeAnalysis.CSharp.CSharpSyntaxVisitor<TResult> visitor) -> TResult
+override Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax.Accept(Microsoft.CodeAnalysis.CSharp.CSharpSyntaxVisitor visitor) -> void
+override Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax.Accept<TResult>(Microsoft.CodeAnalysis.CSharp.CSharpSyntaxVisitor<TResult> visitor) -> TResult
+static Microsoft.CodeAnalysis.CSharp.CSharpExtensions.GetConversion(this Microsoft.CodeAnalysis.Semantics.IConversionExpression conversionExpression) -> Microsoft.CodeAnalysis.CSharp.Conversion
+static Microsoft.CodeAnalysis.CSharp.SyntaxFactory.DeconstructionPattern(Microsoft.CodeAnalysis.CSharp.Syntax.TypeSyntax type, Microsoft.CodeAnalysis.SeparatedSyntaxList<Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax> subPatterns, Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax propertySubpattern, Microsoft.CodeAnalysis.CSharp.Syntax.VariableDesignationSyntax designation) -> Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax
+static Microsoft.CodeAnalysis.CSharp.SyntaxFactory.DeconstructionPattern(Microsoft.CodeAnalysis.CSharp.Syntax.TypeSyntax type, Microsoft.CodeAnalysis.SyntaxToken openParenToken, Microsoft.CodeAnalysis.SeparatedSyntaxList<Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax> subPatterns, Microsoft.CodeAnalysis.SyntaxToken closeParenToken, Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax propertySubpattern, Microsoft.CodeAnalysis.CSharp.Syntax.VariableDesignationSyntax designation) -> Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax
+static Microsoft.CodeAnalysis.CSharp.SyntaxFactory.DeconstructionPattern(Microsoft.CodeAnalysis.SeparatedSyntaxList<Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax> subPatterns = default(Microsoft.CodeAnalysis.SeparatedSyntaxList<Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax>)) -> Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax
+static Microsoft.CodeAnalysis.CSharp.SyntaxFactory.PropertyPattern() -> Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax
+static Microsoft.CodeAnalysis.CSharp.SyntaxFactory.PropertyPattern(Microsoft.CodeAnalysis.CSharp.Syntax.TypeSyntax type, Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax propertySubpattern, Microsoft.CodeAnalysis.CSharp.Syntax.VariableDesignationSyntax designation) -> Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax
+static Microsoft.CodeAnalysis.CSharp.SyntaxFactory.PropertySubpattern(Microsoft.CodeAnalysis.SeparatedSyntaxList<Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax> subPatterns = default(Microsoft.CodeAnalysis.SeparatedSyntaxList<Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax>)) -> Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax
+static Microsoft.CodeAnalysis.CSharp.SyntaxFactory.PropertySubpattern(Microsoft.CodeAnalysis.SyntaxToken openBraceToken, Microsoft.CodeAnalysis.SeparatedSyntaxList<Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax> subPatterns, Microsoft.CodeAnalysis.SyntaxToken closeBraceToken) -> Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax
 static Microsoft.CodeAnalysis.CSharp.SyntaxFactory.RefType(Microsoft.CodeAnalysis.SyntaxToken refKeyword, Microsoft.CodeAnalysis.SyntaxToken readOnlyKeyword, Microsoft.CodeAnalysis.CSharp.Syntax.TypeSyntax type) -> Microsoft.CodeAnalysis.CSharp.Syntax.RefTypeSyntax
-Microsoft.CodeAnalysis.CSharp.Conversion.IsStackAlloc.get -> bool
\ No newline at end of file
+static Microsoft.CodeAnalysis.CSharp.SyntaxFactory.SubpatternElement(Microsoft.CodeAnalysis.CSharp.Syntax.NameColonSyntax nameColon, Microsoft.CodeAnalysis.CSharp.Syntax.PatternSyntax pattern) -> Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax
+static Microsoft.CodeAnalysis.CSharp.SyntaxFactory.SubpatternElement(Microsoft.CodeAnalysis.CSharp.Syntax.PatternSyntax pattern) -> Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax
+virtual Microsoft.CodeAnalysis.CSharp.CSharpSyntaxVisitor.VisitDeconstructionPattern(Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax node) -> void
+virtual Microsoft.CodeAnalysis.CSharp.CSharpSyntaxVisitor.VisitPropertyPattern(Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax node) -> void
+virtual Microsoft.CodeAnalysis.CSharp.CSharpSyntaxVisitor.VisitPropertySubpattern(Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax node) -> void
+virtual Microsoft.CodeAnalysis.CSharp.CSharpSyntaxVisitor.VisitSubpatternElement(Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax node) -> void
+virtual Microsoft.CodeAnalysis.CSharp.CSharpSyntaxVisitor<TResult>.VisitDeconstructionPattern(Microsoft.CodeAnalysis.CSharp.Syntax.DeconstructionPatternSyntax node) -> TResult
+virtual Microsoft.CodeAnalysis.CSharp.CSharpSyntaxVisitor<TResult>.VisitPropertyPattern(Microsoft.CodeAnalysis.CSharp.Syntax.PropertyPatternSyntax node) -> TResult
+virtual Microsoft.CodeAnalysis.CSharp.CSharpSyntaxVisitor<TResult>.VisitPropertySubpattern(Microsoft.CodeAnalysis.CSharp.Syntax.PropertySubpatternSyntax node) -> TResult
+virtual Microsoft.CodeAnalysis.CSharp.CSharpSyntaxVisitor<TResult>.VisitSubpatternElement(Microsoft.CodeAnalysis.CSharp.Syntax.SubpatternElementSyntax node) -> TResult
\ No newline at end of file

src/Compilers/CSharp/Portable/Syntax/Syntax.xml

@@ -1720,12 +1720,52 @@
   <AbstractNode Name="PatternSyntax" Base="CSharpSyntaxNode" />
   <Node Name="DeclarationPatternSyntax" Base="PatternSyntax">
     <Kind Name="DeclarationPattern" />
-    <Field Name="Type" Type="TypeSyntax" />
+    <Field Name="Type" Type="TypeSyntax"/>
     <Field Name="Designation" Type="VariableDesignationSyntax">
       <Kind Name="SingleVariableDesignation"/>
       <Kind Name="DiscardDesignation"/>
     </Field>
   </Node>
+  <Node Name="DeconstructionPatternSyntax" Base="PatternSyntax">
+    <Kind Name="DeconstructionPattern" />
+    <Field Name="Type" Type="TypeSyntax" Optional="true" />
+    <Field Name="OpenParenToken" Type="SyntaxToken">
+      <Kind Name="OpenParenToken"/>
+    </Field>
+    <Field Name="SubPatterns" Type="SeparatedSyntaxList&lt;SubpatternElementSyntax&gt;"/>
+    <Field Name="CloseParenToken" Type="SyntaxToken">
+      <Kind Name="CloseParenToken"/>
+    </Field>
+    <Field Name="PropertySubpattern" Type="PropertySubpatternSyntax" Optional="true" />
+    <Field Name="Designation" Type="VariableDesignationSyntax" Optional="true">
+      <Kind Name="SingleVariableDesignation"/>
+      <Kind Name="DiscardDesignation"/>
+    </Field>
+  </Node>
+  <Node Name="SubpatternElementSyntax" Base="CSharpSyntaxNode">
+    <Kind Name="SubpatternElement"/>
+    <Field Name="NameColon" Type="NameColonSyntax" Optional="true" />
+    <Field Name="Pattern" Type="PatternSyntax" />
+  </Node>
+  <Node Name="PropertyPatternSyntax" Base="PatternSyntax">
+    <Kind Name="PropertyPattern" />
+    <Field Name="Type" Type="TypeSyntax" Optional="true" />
+    <Field Name="PropertySubpattern" Type="PropertySubpatternSyntax"/>
+    <Field Name="Designation" Type="VariableDesignationSyntax" Optional="true">
+      <Kind Name="SingleVariableDesignation"/>
+      <Kind Name="DiscardDesignation"/>
+    </Field>
+  </Node>
+  <Node Name="PropertySubpatternSyntax" Base="CSharpSyntaxNode">
+    <Kind Name="PropertySubpattern"/>
+    <Field Name="OpenBraceToken" Type="SyntaxToken">
+      <Kind Name="OpenBraceToken"/>
+    </Field>
+    <Field Name="SubPatterns" Type="SeparatedSyntaxList&lt;SubpatternElementSyntax&gt;"/>
+    <Field Name="CloseBraceToken" Type="SyntaxToken">
+      <Kind Name="CloseBraceToken"/>
+    </Field>
+  </Node>
   <Node Name="ConstantPatternSyntax" Base="PatternSyntax">
     <Kind Name="ConstantPattern"/>
     <Field Name="Expression" Type="ExpressionSyntax">
@@ -1851,7 +1891,6 @@
     </Field>
     <Field Name="Value" Type="ExpressionSyntax"/>
   </Node>
-
   <AbstractNode Name="VariableDesignationSyntax" Base="CSharpSyntaxNode">
   </AbstractNode>
   <Node Name="SingleVariableDesignationSyntax" Base="VariableDesignationSyntax">
@@ -1876,7 +1915,6 @@
       <Kind Name="CloseParenToken"/>
     </Field>
   </Node>
-
   <Node Name="ExpressionStatementSyntax" Base="StatementSyntax">
     <Kind Name="ExpressionStatement"/>
     <Field Name="Expression" Type="ExpressionSyntax"/>

src/Compilers/CSharp/Portable/Syntax/SyntaxKind.cs

@@ -556,6 +556,11 @@ public enum SyntaxKind : ushort
         WhenClause = 9013,
         DiscardDesignation = 9014,
 
+        PropertyPattern = 9020,
+        PropertySubpattern = 9021,
+        SubpatternElement = 9022,
+        DeconstructionPattern = 9023,
+
         // Kinds between 9000 and 9039 are "reserved" for pattern matching.
         // Please start with 9040 if you add more kinds below.
 

src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenTupleTest.cs

@@ -14983,24 +14983,21 @@ void Match(object o)
 
             var comp = CreateStandardCompilation(source);
             comp.VerifyDiagnostics(
+                // (7,18): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
+                //             case (int, int) tuple: return;
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "(int, int) tuple").WithArguments("recursive patterns", "patterns2").WithLocation(7, 18),
                 // (7,19): error CS1525: Invalid expression term 'int'
                 //             case (int, int) tuple: return;
                 Diagnostic(ErrorCode.ERR_InvalidExprTerm, "int").WithArguments("int").WithLocation(7, 19),
                 // (7,24): error CS1525: Invalid expression term 'int'
                 //             case (int, int) tuple: return;
                 Diagnostic(ErrorCode.ERR_InvalidExprTerm, "int").WithArguments("int").WithLocation(7, 24),
-                // (7,29): error CS1003: Syntax error, ':' expected
-                //             case (int, int) tuple: return;
-                Diagnostic(ErrorCode.ERR_SyntaxError, "tuple").WithArguments(":", "").WithLocation(7, 29),
-                // (7,18): error CS0150: A constant value is expected
-                //             case (int, int) tuple: return;
-                Diagnostic(ErrorCode.ERR_ConstantExpected, "(int, int)").WithLocation(7, 18),
-                // (7,29): warning CS0162: Unreachable code detected
+                // (7,18): error CS0570: 'recursive pattern' is not supported by the language
                 //             case (int, int) tuple: return;
-                Diagnostic(ErrorCode.WRN_UnreachableCode, "tuple").WithLocation(7, 29),
-                // (7,29): warning CS0164: This label has not been referenced
+                Diagnostic(ErrorCode.ERR_BindToBogus, "(int, int) tuple").WithArguments("recursive pattern").WithLocation(7, 18),
+                // (7,36): warning CS0162: Unreachable code detected
                 //             case (int, int) tuple: return;
-                Diagnostic(ErrorCode.WRN_UnreferencedLabel, "tuple").WithLocation(7, 29)
+                Diagnostic(ErrorCode.WRN_UnreachableCode, "return").WithLocation(7, 36)
                );
         }
 
@@ -15021,9 +15018,12 @@ void Match(object o)
 
             var comp = CreateStandardCompilation(source);
             comp.VerifyDiagnostics(
-                // (7,18): error CS0150: A constant value is expected
+                // (7,18): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
                 //             case (1, 1): return;
-                Diagnostic(ErrorCode.ERR_ConstantExpected, "(1, 1)").WithLocation(7, 18),
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "(1, 1)").WithArguments("recursive patterns", "patterns2").WithLocation(7, 18),
+                // (7,18): error CS0570: 'recursive pattern' is not supported by the language
+                //             case (1, 1): return;
+                Diagnostic(ErrorCode.ERR_BindToBogus, "(1, 1)").WithArguments("recursive pattern").WithLocation(7, 18),
                 // (7,26): warning CS0162: Unreachable code detected
                 //             case (1, 1): return;
                 Diagnostic(ErrorCode.WRN_UnreachableCode, "return").WithLocation(7, 26)
@@ -15047,18 +15047,15 @@ void Match(object o)
 
             var comp = CreateStandardCompilation(source);
             comp.VerifyDiagnostics(
-                // (7,25): error CS1003: Syntax error, ':' expected
-                //             case (1, 1) t: return;
-                Diagnostic(ErrorCode.ERR_SyntaxError, "t").WithArguments(":", "").WithLocation(7, 25),
-                // (7,18): error CS0150: A constant value is expected
+                // (7,18): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
                 //             case (1, 1) t: return;
-                Diagnostic(ErrorCode.ERR_ConstantExpected, "(1, 1)").WithLocation(7, 18),
-                // (7,25): warning CS0162: Unreachable code detected
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "(1, 1) t").WithArguments("recursive patterns", "patterns2").WithLocation(7, 18),
+                // (7,18): error CS0570: 'recursive pattern' is not supported by the language
                 //             case (1, 1) t: return;
-                Diagnostic(ErrorCode.WRN_UnreachableCode, "t").WithLocation(7, 25),
-                // (7,25): warning CS0164: This label has not been referenced
+                Diagnostic(ErrorCode.ERR_BindToBogus, "(1, 1) t").WithArguments("recursive pattern").WithLocation(7, 18),
+                // (7,28): warning CS0162: Unreachable code detected
                 //             case (1, 1) t: return;
-                Diagnostic(ErrorCode.WRN_UnreferencedLabel, "t").WithLocation(7, 25)
+                Diagnostic(ErrorCode.WRN_UnreachableCode, "return").WithLocation(7, 28)
                );
         }
 

src/Compilers/CSharp/Test/Semantic/Semantics/OutVarTests.cs

@@ -30353,7 +30353,7 @@ static void Main(string[] args)
     {
         switch (true)
         {
-            case TakeOutParam(3, out var x1):
+            case 1+TakeOutParam(3, out var x1):
                 System.Console.WriteLine(x1);
                 break;
         }
@@ -30368,9 +30368,9 @@ static bool TakeOutParam(int y, out int x)
             var compilation = CreateCompilationWithMscorlib45(source, options: TestOptions.DebugExe, parseOptions: TestOptions.Regular);
             // The point of this test is that it should not crash.
             compilation.VerifyDiagnostics(
-                // (8,18): error CS0150: A constant value is expected
-                //             case TakeOutParam(3, out var x1):
-                Diagnostic(ErrorCode.ERR_ConstantExpected, "TakeOutParam(3, out var x1)").WithLocation(8, 18),
+                // (8,18): error CS0019: Operator '+' cannot be applied to operands of type 'int' and 'bool'
+                //             case 1+TakeOutParam(3, out var x1):
+                Diagnostic(ErrorCode.ERR_BadBinaryOps, "1+TakeOutParam(3, out var x1)").WithArguments("+", "int", "bool").WithLocation(8, 18),
                 // (9,17): warning CS0162: Unreachable code detected
                 //                 System.Console.WriteLine(x1);
                 Diagnostic(ErrorCode.WRN_UnreachableCode, "System").WithLocation(9, 17)
@@ -30394,7 +30394,7 @@ static void Main(string[] args)
     {
         switch (true)
         {
-            case TakeOutParam(3, out UndelcaredType x1):
+            case 1+TakeOutParam(3, out UndelcaredType x1):
                 System.Console.WriteLine(x1);
                 break;
         }
@@ -30404,12 +30404,12 @@ static void Main(string[] args)
             var compilation = CreateCompilationWithMscorlib45(source, options: TestOptions.DebugExe, parseOptions: TestOptions.Regular);
             // The point of this test is that it should not crash.
             compilation.VerifyDiagnostics(
-                // (8,38): error CS0246: The type or namespace name 'UndelcaredType' could not be found (are you missing a using directive or an assembly reference?)
-                //             case TakeOutParam(3, out UndelcaredType x1):
-                Diagnostic(ErrorCode.ERR_SingleTypeNameNotFound, "UndelcaredType").WithArguments("UndelcaredType").WithLocation(8, 38),
-                // (8,18): error CS0103: The name 'TakeOutParam' does not exist in the current context
-                //             case TakeOutParam(3, out UndelcaredType x1):
-                Diagnostic(ErrorCode.ERR_NameNotInContext, "TakeOutParam").WithArguments("TakeOutParam").WithLocation(8, 18),
+                // (8,20): error CS0103: The name 'TakeOutParam' does not exist in the current context
+                //             case 1+TakeOutParam(3, out UndelcaredType x1):
+                Diagnostic(ErrorCode.ERR_NameNotInContext, "TakeOutParam").WithArguments("TakeOutParam").WithLocation(8, 20),
+                // (8,40): error CS0246: The type or namespace name 'UndelcaredType' could not be found (are you missing a using directive or an assembly reference?)
+                //             case 1+TakeOutParam(3, out UndelcaredType x1):
+                Diagnostic(ErrorCode.ERR_SingleTypeNameNotFound, "UndelcaredType").WithArguments("UndelcaredType").WithLocation(8, 40),
                 // (9,17): warning CS0162: Unreachable code detected
                 //                 System.Console.WriteLine(x1);
                 Diagnostic(ErrorCode.WRN_UnreachableCode, "System").WithLocation(9, 17)
@@ -32138,10 +32138,10 @@ public static void Main(string[] args)
     {
         switch ((object)args.Length)
         {
-            case M(nameof(M(out int z1)), z1):
+            case 1+M(nameof(M(out int z1)), z1):
                 System.Console.WriteLine(z1);
                 break;
-            case M(nameof(M(out var z2)), z2):
+            case 1+M(nameof(M(out var z2)), z2):
                 System.Console.WriteLine(z2);
                 break;
         }
@@ -32152,18 +32152,18 @@ public static void Main(string[] args)
 ";
             var compilation = CreateCompilationWithMscorlib45(text);
             compilation.VerifyDiagnostics(
-                // (8,27): error CS8081: Expression does not have a name.
-                //             case M(nameof(M(out int z1)), z1):
-                Diagnostic(ErrorCode.ERR_ExpressionHasNoName, "M(out int z1)").WithLocation(8, 27),
-                // (8,18): error CS0150: A constant value is expected
-                //             case M(nameof(M(out int z1)), z1):
-                Diagnostic(ErrorCode.ERR_ConstantExpected, "M(nameof(M(out int z1)), z1)").WithLocation(8, 18),
-                // (11,27): error CS8081: Expression does not have a name.
-                //             case M(nameof(M(out var z2)), z2):
-                Diagnostic(ErrorCode.ERR_ExpressionHasNoName, "M(out var z2)").WithLocation(11, 27),
-                // (11,18): error CS0150: A constant value is expected
-                //             case M(nameof(M(out var z2)), z2):
-                Diagnostic(ErrorCode.ERR_ConstantExpected, "M(nameof(M(out var z2)), z2)").WithLocation(11, 18),
+                // (8,29): error CS8081: Expression does not have a name.
+                //             case 1+M(nameof(M(out int z1)), z1):
+                Diagnostic(ErrorCode.ERR_ExpressionHasNoName, "M(out int z1)").WithLocation(8, 29),
+                // (8,18): error CS0019: Operator '+' cannot be applied to operands of type 'int' and 'bool'
+                //             case 1+M(nameof(M(out int z1)), z1):
+                Diagnostic(ErrorCode.ERR_BadBinaryOps, "1+M(nameof(M(out int z1)), z1)").WithArguments("+", "int", "bool").WithLocation(8, 18),
+                // (11,29): error CS8081: Expression does not have a name.
+                //             case 1+M(nameof(M(out var z2)), z2):
+                Diagnostic(ErrorCode.ERR_ExpressionHasNoName, "M(out var z2)").WithLocation(11, 29),
+                // (11,18): error CS0019: Operator '+' cannot be applied to operands of type 'int' and 'bool'
+                //             case 1+M(nameof(M(out var z2)), z2):
+                Diagnostic(ErrorCode.ERR_BadBinaryOps, "1+M(nameof(M(out var z2)), z2)").WithArguments("+", "int", "bool").WithLocation(11, 18),
                 // (9,17): warning CS0162: Unreachable code detected
                 //                 System.Console.WriteLine(z1);
                 Diagnostic(ErrorCode.WRN_UnreachableCode, "System").WithLocation(9, 17),

src/Compilers/CSharp/Test/Semantic/Semantics/PatternSwitchTests.cs

@@ -1512,69 +1512,63 @@ static void M(object o)
 ";
             var compilation = CreateCompilationWithMscorlib45(source, options: TestOptions.DebugDll);
             compilation.VerifyDiagnostics(
+                // (21,18): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
+                //             case (int, int):
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "(int, int)").WithArguments("recursive patterns", "patterns2").WithLocation(21, 18),
                 // (21,19): error CS1525: Invalid expression term 'int'
                 //             case (int, int):
                 Diagnostic(ErrorCode.ERR_InvalidExprTerm, "int").WithArguments("int").WithLocation(21, 19),
                 // (21,24): error CS1525: Invalid expression term 'int'
                 //             case (int, int):
                 Diagnostic(ErrorCode.ERR_InvalidExprTerm, "int").WithArguments("int").WithLocation(21, 24),
+                // (22,18): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
+                //             case (int x, int y):
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "(int x, int y)").WithArguments("recursive patterns", "patterns2").WithLocation(22, 18),
+                // (23,18): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
+                //             case (int, int) z:
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "(int, int) z").WithArguments("recursive patterns", "patterns2").WithLocation(23, 18),
                 // (23,19): error CS1525: Invalid expression term 'int'
                 //             case (int, int) z:
                 Diagnostic(ErrorCode.ERR_InvalidExprTerm, "int").WithArguments("int").WithLocation(23, 19),
                 // (23,24): error CS1525: Invalid expression term 'int'
                 //             case (int, int) z:
                 Diagnostic(ErrorCode.ERR_InvalidExprTerm, "int").WithArguments("int").WithLocation(23, 24),
-                // (23,29): error CS1003: Syntax error, ':' expected
-                //             case (int, int) z:
-                Diagnostic(ErrorCode.ERR_SyntaxError, "z").WithArguments(":", "").WithLocation(23, 29),
-                // (23,31): error CS1525: Invalid expression term 'case'
-                //             case (int, int) z:
-                Diagnostic(ErrorCode.ERR_InvalidExprTerm, "").WithArguments("case").WithLocation(23, 31),
-                // (23,31): error CS1002: ; expected
-                //             case (int, int) z:
-                Diagnostic(ErrorCode.ERR_SemicolonExpected, "").WithLocation(23, 31),
-                // (24,33): error CS1003: Syntax error, ':' expected
-                //             case (int a, int b) c:
-                Diagnostic(ErrorCode.ERR_SyntaxError, "c").WithArguments(":", "").WithLocation(24, 33),
-                // (24,35): error CS1525: Invalid expression term 'case'
-                //             case (int a, int b) c:
-                Diagnostic(ErrorCode.ERR_InvalidExprTerm, "").WithArguments("case").WithLocation(24, 35),
-                // (24,35): error CS1002: ; expected
+                // (24,18): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
                 //             case (int a, int b) c:
-                Diagnostic(ErrorCode.ERR_SemicolonExpected, "").WithLocation(24, 35),
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "(int a, int b) c").WithArguments("recursive patterns", "patterns2").WithLocation(24, 18),
+                // (25,18): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
+                //             case (long, long) d:
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "(long, long) d").WithArguments("recursive patterns", "patterns2").WithLocation(25, 18),
                 // (25,19): error CS1525: Invalid expression term 'long'
                 //             case (long, long) d:
                 Diagnostic(ErrorCode.ERR_InvalidExprTerm, "long").WithArguments("long").WithLocation(25, 19),
                 // (25,25): error CS1525: Invalid expression term 'long'
                 //             case (long, long) d:
                 Diagnostic(ErrorCode.ERR_InvalidExprTerm, "long").WithArguments("long").WithLocation(25, 25),
-                // (25,31): error CS1003: Syntax error, ':' expected
-                //             case (long, long) d:
-                Diagnostic(ErrorCode.ERR_SyntaxError, "d").WithArguments(":", "").WithLocation(25, 31),
+                // (30,18): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
+                //             case (int, int) z:
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "(int, int) z").WithArguments("recursive patterns", "patterns2").WithLocation(30, 18),
                 // (30,19): error CS1525: Invalid expression term 'int'
                 //             case (int, int) z:
                 Diagnostic(ErrorCode.ERR_InvalidExprTerm, "int").WithArguments("int").WithLocation(30, 19),
                 // (30,24): error CS1525: Invalid expression term 'int'
                 //             case (int, int) z:
                 Diagnostic(ErrorCode.ERR_InvalidExprTerm, "int").WithArguments("int").WithLocation(30, 24),
-                // (30,29): error CS1003: Syntax error, ':' expected
-                //             case (int, int) z:
-                Diagnostic(ErrorCode.ERR_SyntaxError, "z").WithArguments(":", "").WithLocation(30, 29),
+                // (32,18): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
+                //             case (long, long) d:
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "(long, long) d").WithArguments("recursive patterns", "patterns2").WithLocation(32, 18),
                 // (32,19): error CS1525: Invalid expression term 'long'
                 //             case (long, long) d:
                 Diagnostic(ErrorCode.ERR_InvalidExprTerm, "long").WithArguments("long").WithLocation(32, 19),
                 // (32,25): error CS1525: Invalid expression term 'long'
                 //             case (long, long) d:
                 Diagnostic(ErrorCode.ERR_InvalidExprTerm, "long").WithArguments("long").WithLocation(32, 25),
-                // (32,31): error CS1003: Syntax error, ':' expected
-                //             case (long, long) d:
-                Diagnostic(ErrorCode.ERR_SyntaxError, "d").WithArguments(":", "").WithLocation(32, 31),
-                // (37,47): error CS1003: Syntax error, ':' expected
+                // (37,18): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
                 //             case (System.Int32, System.Int32) z:
-                Diagnostic(ErrorCode.ERR_SyntaxError, "z").WithArguments(":", "").WithLocation(37, 47),
-                // (39,47): error CS1003: Syntax error, ':' expected
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "(System.Int32, System.Int32) z").WithArguments("recursive patterns", "patterns2").WithLocation(37, 18),
+                // (39,18): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
                 //             case (System.Int64, System.Int64) d:
-                Diagnostic(ErrorCode.ERR_SyntaxError, "d").WithArguments(":", "").WithLocation(39, 47),
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "(System.Int64, System.Int64) d").WithArguments("recursive patterns", "patterns2").WithLocation(39, 18),
                 // (43,23): error CS1525: Invalid expression term 'int'
                 //             if (o is (int, int)) {}
                 Diagnostic(ErrorCode.ERR_InvalidExprTerm, "int").WithArguments("int").WithLocation(43, 23),
@@ -1623,51 +1617,33 @@ static void M(object o)
                 // (52,56): error CS1513: } expected
                 //             if (o is (System.Int32 a, System.Int32 b) c) {}
                 Diagnostic(ErrorCode.ERR_RbraceExpected, ")").WithLocation(52, 56),
-                // (21,18): error CS0150: A constant value is expected
+                // (21,18): error CS0570: 'recursive pattern' is not supported by the language
                 //             case (int, int):
-                Diagnostic(ErrorCode.ERR_ConstantExpected, "(int, int)").WithLocation(21, 18),
-                // (22,19): error CS8185: A declaration is not allowed in this context.
-                //             case (int x, int y):
-                Diagnostic(ErrorCode.ERR_DeclarationExpressionNotPermitted, "int x").WithLocation(22, 19),
-                // (22,26): error CS8185: A declaration is not allowed in this context.
+                Diagnostic(ErrorCode.ERR_BindToBogus, "(int, int)").WithArguments("recursive pattern").WithLocation(21, 18),
+                // (22,18): error CS0570: 'recursive pattern' is not supported by the language
                 //             case (int x, int y):
-                Diagnostic(ErrorCode.ERR_DeclarationExpressionNotPermitted, "int y").WithLocation(22, 26),
-                // (22,18): error CS0150: A constant value is expected
-                //             case (int x, int y):
-                Diagnostic(ErrorCode.ERR_ConstantExpected, "(int x, int y)").WithLocation(22, 18),
-                // (23,18): error CS0150: A constant value is expected
+                Diagnostic(ErrorCode.ERR_BindToBogus, "(int x, int y)").WithArguments("recursive pattern").WithLocation(22, 18),
+                // (23,18): error CS0570: 'recursive pattern' is not supported by the language
                 //             case (int, int) z:
-                Diagnostic(ErrorCode.ERR_ConstantExpected, "(int, int)").WithLocation(23, 18),
-                // (24,19): error CS8185: A declaration is not allowed in this context.
-                //             case (int a, int b) c:
-                Diagnostic(ErrorCode.ERR_DeclarationExpressionNotPermitted, "int a").WithLocation(24, 19),
-                // (24,26): error CS8185: A declaration is not allowed in this context.
-                //             case (int a, int b) c:
-                Diagnostic(ErrorCode.ERR_DeclarationExpressionNotPermitted, "int b").WithLocation(24, 26),
-                // (24,18): error CS0150: A constant value is expected
+                Diagnostic(ErrorCode.ERR_BindToBogus, "(int, int) z").WithArguments("recursive pattern").WithLocation(23, 18),
+                // (24,18): error CS0570: 'recursive pattern' is not supported by the language
                 //             case (int a, int b) c:
-                Diagnostic(ErrorCode.ERR_ConstantExpected, "(int a, int b)").WithLocation(24, 18),
-                // (25,18): error CS0150: A constant value is expected
+                Diagnostic(ErrorCode.ERR_BindToBogus, "(int a, int b) c").WithArguments("recursive pattern").WithLocation(24, 18),
+                // (25,18): error CS0570: 'recursive pattern' is not supported by the language
                 //             case (long, long) d:
-                Diagnostic(ErrorCode.ERR_ConstantExpected, "(long, long)").WithLocation(25, 18),
-                // (30,18): error CS0150: A constant value is expected
+                Diagnostic(ErrorCode.ERR_BindToBogus, "(long, long) d").WithArguments("recursive pattern").WithLocation(25, 18),
+                // (30,18): error CS0570: 'recursive pattern' is not supported by the language
                 //             case (int, int) z:
-                Diagnostic(ErrorCode.ERR_ConstantExpected, "(int, int)").WithLocation(30, 18),
-                // (32,18): error CS0150: A constant value is expected
+                Diagnostic(ErrorCode.ERR_BindToBogus, "(int, int) z").WithArguments("recursive pattern").WithLocation(30, 18),
+                // (32,18): error CS0570: 'recursive pattern' is not supported by the language
                 //             case (long, long) d:
-                Diagnostic(ErrorCode.ERR_ConstantExpected, "(long, long)").WithLocation(32, 18),
-                // (37,19): error CS0119: 'int' is a type, which is not valid in the given context
+                Diagnostic(ErrorCode.ERR_BindToBogus, "(long, long) d").WithArguments("recursive pattern").WithLocation(32, 18),
+                // (37,18): error CS0570: 'recursive pattern' is not supported by the language
                 //             case (System.Int32, System.Int32) z:
-                Diagnostic(ErrorCode.ERR_BadSKunknown, "System.Int32").WithArguments("int", "type").WithLocation(37, 19),
-                // (37,33): error CS0119: 'int' is a type, which is not valid in the given context
-                //             case (System.Int32, System.Int32) z:
-                Diagnostic(ErrorCode.ERR_BadSKunknown, "System.Int32").WithArguments("int", "type").WithLocation(37, 33),
-                // (39,19): error CS0119: 'long' is a type, which is not valid in the given context
-                //             case (System.Int64, System.Int64) d:
-                Diagnostic(ErrorCode.ERR_BadSKunknown, "System.Int64").WithArguments("long", "type").WithLocation(39, 19),
-                // (39,33): error CS0119: 'long' is a type, which is not valid in the given context
+                Diagnostic(ErrorCode.ERR_BindToBogus, "(System.Int32, System.Int32) z").WithArguments("recursive pattern").WithLocation(37, 18),
+                // (39,18): error CS0570: 'recursive pattern' is not supported by the language
                 //             case (System.Int64, System.Int64) d:
-                Diagnostic(ErrorCode.ERR_BadSKunknown, "System.Int64").WithArguments("long", "type").WithLocation(39, 33),
+                Diagnostic(ErrorCode.ERR_BindToBogus, "(System.Int64, System.Int64) d").WithArguments("recursive pattern").WithLocation(39, 18),
                 // (43,22): error CS0150: A constant value is expected
                 //             if (o is (int, int)) {}
                 Diagnostic(ErrorCode.ERR_ConstantExpected, "(int, int)").WithLocation(43, 22),
@@ -1734,48 +1710,21 @@ static void M(object o)
                 // (52,55): error CS0103: The name 'c' does not exist in the current context
                 //             if (o is (System.Int32 a, System.Int32 b) c) {}
                 Diagnostic(ErrorCode.ERR_NameNotInContext, "c").WithArguments("c").WithLocation(52, 55),
-                // (23,29): warning CS0162: Unreachable code detected
-                //             case (int, int) z:
-                Diagnostic(ErrorCode.WRN_UnreachableCode, "z").WithLocation(23, 29),
-                // (24,33): warning CS0162: Unreachable code detected
-                //             case (int a, int b) c:
-                Diagnostic(ErrorCode.WRN_UnreachableCode, "c").WithLocation(24, 33),
-                // (25,31): warning CS0162: Unreachable code detected
-                //             case (long, long) d:
-                Diagnostic(ErrorCode.WRN_UnreachableCode, "d").WithLocation(25, 31),
-                // (30,29): warning CS0162: Unreachable code detected
-                //             case (int, int) z:
-                Diagnostic(ErrorCode.WRN_UnreachableCode, "z").WithLocation(30, 29),
-                // (32,31): warning CS0162: Unreachable code detected
-                //             case (long, long) d:
-                Diagnostic(ErrorCode.WRN_UnreachableCode, "d").WithLocation(32, 31),
-                // (37,47): warning CS0162: Unreachable code detected
-                //             case (System.Int32, System.Int32) z:
-                Diagnostic(ErrorCode.WRN_UnreachableCode, "z").WithLocation(37, 47),
-                // (39,47): warning CS0162: Unreachable code detected
-                //             case (System.Int64, System.Int64) d:
-                Diagnostic(ErrorCode.WRN_UnreachableCode, "d").WithLocation(39, 47),
-                // (23,29): warning CS0164: This label has not been referenced
-                //             case (int, int) z:
-                Diagnostic(ErrorCode.WRN_UnreferencedLabel, "z").WithLocation(23, 29),
-                // (24,33): warning CS0164: This label has not been referenced
-                //             case (int a, int b) c:
-                Diagnostic(ErrorCode.WRN_UnreferencedLabel, "c").WithLocation(24, 33),
-                // (25,31): warning CS0164: This label has not been referenced
-                //             case (long, long) d:
-                Diagnostic(ErrorCode.WRN_UnreferencedLabel, "d").WithLocation(25, 31),
-                // (30,29): warning CS0164: This label has not been referenced
-                //             case (int, int) z:
-                Diagnostic(ErrorCode.WRN_UnreferencedLabel, "z").WithLocation(30, 29),
-                // (32,31): warning CS0164: This label has not been referenced
-                //             case (long, long) d:
-                Diagnostic(ErrorCode.WRN_UnreferencedLabel, "d").WithLocation(32, 31),
-                // (37,47): warning CS0164: This label has not been referenced
-                //             case (System.Int32, System.Int32) z:
-                Diagnostic(ErrorCode.WRN_UnreferencedLabel, "z").WithLocation(37, 47),
-                // (39,47): warning CS0164: This label has not been referenced
-                //             case (System.Int64, System.Int64) d:
-                Diagnostic(ErrorCode.WRN_UnreferencedLabel, "d").WithLocation(39, 47),
+                // (26,17): warning CS0162: Unreachable code detected
+                //                 break;
+                Diagnostic(ErrorCode.WRN_UnreachableCode, "break").WithLocation(26, 17),
+                // (31,17): warning CS0162: Unreachable code detected
+                //                 break;
+                Diagnostic(ErrorCode.WRN_UnreachableCode, "break").WithLocation(31, 17),
+                // (33,17): warning CS0162: Unreachable code detected
+                //                 break;
+                Diagnostic(ErrorCode.WRN_UnreachableCode, "break").WithLocation(33, 17),
+                // (38,17): warning CS0162: Unreachable code detected
+                //                 break;
+                Diagnostic(ErrorCode.WRN_UnreachableCode, "break").WithLocation(38, 17),
+                // (40,17): warning CS0162: Unreachable code detected
+                //                 break;
+                Diagnostic(ErrorCode.WRN_UnreachableCode, "break").WithLocation(40, 17),
                 // (44,23): error CS0165: Use of unassigned local variable 'x'
                 //             if (o is (int x, int y)) {}
                 Diagnostic(ErrorCode.ERR_UseDefViolation, "int x").WithArguments("x").WithLocation(44, 23),

src/Compilers/CSharp/Test/Semantic/Semantics/SwitchTests.cs

@@ -1160,26 +1160,65 @@ static object F(int i)
 ";
 
             CreateStandardCompilation(text, parseOptions: TestOptions.Regular6).VerifyDiagnostics(
+                // (8,13): error CS8059: Feature 'pattern matching' is not available in C# 6. Please use language version 7.0 or greater.
+                //             case ((o.GetType().Name.Length)):
+                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion6, "case ((o.GetType().Name.Length)):").WithArguments("pattern matching", "7.0").WithLocation(8, 13),
+                // (8,18): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
+                //             case ((o.GetType().Name.Length)):
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "((o.GetType().Name.Length))").WithArguments("recursive patterns", "patterns2").WithLocation(8, 18),
+                // (8,19): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
+                //             case ((o.GetType().Name.Length)):
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "(o.GetType().Name.Length)").WithArguments("recursive patterns", "patterns2").WithLocation(8, 19),
+                // (8,20): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
+                //             case ((o.GetType().Name.Length)):
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "o.GetType()").WithArguments("recursive patterns", "patterns2").WithLocation(8, 20),
+                // (8,31): error CS1003: Syntax error, ',' expected
+                //             case ((o.GetType().Name.Length)):
+                Diagnostic(ErrorCode.ERR_SyntaxError, ".").WithArguments(",", ".").WithLocation(8, 31),
+                // (8,32): error CS1003: Syntax error, ',' expected
+                //             case ((o.GetType().Name.Length)):
+                Diagnostic(ErrorCode.ERR_SyntaxError, "Name").WithArguments(",", "").WithLocation(8, 32),
                 // (6,17): error CS0151: A switch expression or case label must be a bool, char, string, integral, enum, or corresponding nullable type in C# 6 and earlier.
                 //         switch (o)
                 Diagnostic(ErrorCode.ERR_V6SwitchGoverningTypeValueExpected, "o").WithLocation(6, 17),
-                // (8,18): error CS0150: A constant value is expected
+                // (8,18): error CS0570: 'recursive pattern' is not supported by the language
                 //             case ((o.GetType().Name.Length)):
-                Diagnostic(ErrorCode.ERR_ConstantExpected, "((o.GetType().Name.Length))").WithLocation(8, 18),
+                Diagnostic(ErrorCode.ERR_BindToBogus, "((o.GetType().Name.Length))").WithArguments("recursive pattern").WithLocation(8, 18),
                 // (9,17): error CS7036: There is no argument given that corresponds to the required formal parameter 'o' of 'C.M(object)'
                 //                 M();
                 Diagnostic(ErrorCode.ERR_NoCorrespondingArgument, "M").WithArguments("o", "C.M(object)").WithLocation(9, 17),
-                // (12,13): error CS0152: The switch statement contains multiple cases with the label value '0'
+                // (12,13): error CS8120: The switch case has already been handled by a previous case.
                 //             case 0:
-                Diagnostic(ErrorCode.ERR_DuplicateCaseLabel, "case 0:").WithArguments("0").WithLocation(12, 13)
+                Diagnostic(ErrorCode.ERR_PatternIsSubsumed, "case 0:").WithLocation(12, 13),
+                // (9,17): warning CS0162: Unreachable code detected
+                //                 M();
+                Diagnostic(ErrorCode.WRN_UnreachableCode, "M").WithLocation(9, 17)
                 );
             CreateStandardCompilation(text, parseOptions: TestOptions.Regular6WithV7SwitchBinder).VerifyDiagnostics(
+                // (8,13): error CS8059: Feature 'pattern matching' is not available in C# 6. Please use language version 7.0 or greater.
+                //             case ((o.GetType().Name.Length)):
+                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion6, "case ((o.GetType().Name.Length)):").WithArguments("pattern matching", "7.0").WithLocation(8, 13),
+                // (8,18): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
+                //             case ((o.GetType().Name.Length)):
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "((o.GetType().Name.Length))").WithArguments("recursive patterns", "patterns2").WithLocation(8, 18),
+                // (8,19): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
+                //             case ((o.GetType().Name.Length)):
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "(o.GetType().Name.Length)").WithArguments("recursive patterns", "patterns2").WithLocation(8, 19),
+                // (8,20): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
+                //             case ((o.GetType().Name.Length)):
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "o.GetType()").WithArguments("recursive patterns", "patterns2").WithLocation(8, 20),
+                // (8,31): error CS1003: Syntax error, ',' expected
+                //             case ((o.GetType().Name.Length)):
+                Diagnostic(ErrorCode.ERR_SyntaxError, ".").WithArguments(",", ".").WithLocation(8, 31),
+                // (8,32): error CS1003: Syntax error, ',' expected
+                //             case ((o.GetType().Name.Length)):
+                Diagnostic(ErrorCode.ERR_SyntaxError, "Name").WithArguments(",", "").WithLocation(8, 32),
                 // (6,17): error CS0151: A switch expression or case label must be a bool, char, string, integral, enum, or corresponding nullable type in C# 6 and earlier.
                 //         switch (o)
                 Diagnostic(ErrorCode.ERR_V6SwitchGoverningTypeValueExpected, "o").WithLocation(6, 17),
-                // (8,18): error CS0150: A constant value is expected
+                // (8,18): error CS0570: 'recursive pattern' is not supported by the language
                 //             case ((o.GetType().Name.Length)):
-                Diagnostic(ErrorCode.ERR_ConstantExpected, "((o.GetType().Name.Length))").WithLocation(8, 18),
+                Diagnostic(ErrorCode.ERR_BindToBogus, "((o.GetType().Name.Length))").WithArguments("recursive pattern").WithLocation(8, 18),
                 // (9,17): error CS7036: There is no argument given that corresponds to the required formal parameter 'o' of 'C.M(object)'
                 //                 M();
                 Diagnostic(ErrorCode.ERR_NoCorrespondingArgument, "M").WithArguments("o", "C.M(object)").WithLocation(9, 17),
@@ -1191,9 +1230,24 @@ static object F(int i)
                 Diagnostic(ErrorCode.WRN_UnreachableCode, "M").WithLocation(9, 17)
                 );
             CreateStandardCompilation(text).VerifyDiagnostics(
-                // (8,18): error CS0150: A constant value is expected
+                // (8,18): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
+                //             case ((o.GetType().Name.Length)):
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "((o.GetType().Name.Length))").WithArguments("recursive patterns", "patterns2").WithLocation(8, 18),
+                // (8,19): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
+                //             case ((o.GetType().Name.Length)):
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "(o.GetType().Name.Length)").WithArguments("recursive patterns", "patterns2").WithLocation(8, 19),
+                // (8,20): error CS8058: Feature 'recursive patterns' is experimental and unsupported; use '/features:patterns2' to enable.
+                //             case ((o.GetType().Name.Length)):
+                Diagnostic(ErrorCode.ERR_FeatureIsExperimental, "o.GetType()").WithArguments("recursive patterns", "patterns2").WithLocation(8, 20),
+                // (8,31): error CS1003: Syntax error, ',' expected
+                //             case ((o.GetType().Name.Length)):
+                Diagnostic(ErrorCode.ERR_SyntaxError, ".").WithArguments(",", ".").WithLocation(8, 31),
+                // (8,32): error CS1003: Syntax error, ',' expected
+                //             case ((o.GetType().Name.Length)):
+                Diagnostic(ErrorCode.ERR_SyntaxError, "Name").WithArguments(",", "").WithLocation(8, 32),
+                // (8,18): error CS0570: 'recursive pattern' is not supported by the language
                 //             case ((o.GetType().Name.Length)):
-                Diagnostic(ErrorCode.ERR_ConstantExpected, "((o.GetType().Name.Length))").WithLocation(8, 18),
+                Diagnostic(ErrorCode.ERR_BindToBogus, "((o.GetType().Name.Length))").WithArguments("recursive pattern").WithLocation(8, 18),
                 // (9,17): error CS7036: There is no argument given that corresponds to the required formal parameter 'o' of 'C.M(object)'
                 //                 M();
                 Diagnostic(ErrorCode.ERR_NoCorrespondingArgument, "M").WithArguments("o", "C.M(object)").WithLocation(9, 17),

src/Compilers/CSharp/Test/Syntax/Generated/Syntax.Test.xml.Generated.cs

@@ -379,6 +379,26 @@ private static Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.DeclarationPa
             return Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.SyntaxFactory.DeclarationPattern(GenerateIdentifierName(), GenerateSingleVariableDesignation());
         }
         
+        private static Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.DeconstructionPatternSyntax GenerateDeconstructionPattern()
+        {
+            return Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.SyntaxFactory.DeconstructionPattern(null, Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.SyntaxFactory.Token(SyntaxKind.OpenParenToken), new Microsoft.CodeAnalysis.Syntax.InternalSyntax.SeparatedSyntaxList<Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.SubpatternElementSyntax>(), Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.SyntaxFactory.Token(SyntaxKind.CloseParenToken), null, null);
+        }
+        
+        private static Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.SubpatternElementSyntax GenerateSubpatternElement()
+        {
+            return Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.SyntaxFactory.SubpatternElement(null, GenerateDeclarationPattern());
+        }
+        
+        private static Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.PropertyPatternSyntax GeneratePropertyPattern()
+        {
+            return Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.SyntaxFactory.PropertyPattern(null, GeneratePropertySubpattern(), null);
+        }
+        
+        private static Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.PropertySubpatternSyntax GeneratePropertySubpattern()
+        {
+            return Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.SyntaxFactory.PropertySubpattern(Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.SyntaxFactory.Token(SyntaxKind.OpenBraceToken), new Microsoft.CodeAnalysis.Syntax.InternalSyntax.SeparatedSyntaxList<Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.SubpatternElementSyntax>(), Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.SyntaxFactory.Token(SyntaxKind.CloseBraceToken));
+        }
+        
         private static Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.ConstantPatternSyntax GenerateConstantPattern()
         {
             return Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax.SyntaxFactory.ConstantPattern(GenerateIdentifierName());
@@ -1906,6 +1926,56 @@ public void TestDeclarationPatternFactoryAndProperties()
             AttachAndCheckDiagnostics(node);
         }
         
+        [Fact]
+        public void TestDeconstructionPatternFactoryAndProperties()
+        {
+            var node = GenerateDeconstructionPattern();
+            
+            Assert.Null(node.Type);
+            Assert.Equal(SyntaxKind.OpenParenToken, node.OpenParenToken.Kind);
+            Assert.NotNull(node.SubPatterns);
+            Assert.Equal(SyntaxKind.CloseParenToken, node.CloseParenToken.Kind);
+            Assert.Null(node.PropertySubpattern);
+            Assert.Null(node.Designation);
+            
+            AttachAndCheckDiagnostics(node);
+        }
+        
+        [Fact]
+        public void TestSubpatternElementFactoryAndProperties()
+        {
+            var node = GenerateSubpatternElement();
+            
+            Assert.Null(node.NameColon);
+            Assert.NotNull(node.Pattern);
+            
+            AttachAndCheckDiagnostics(node);
+        }
+        
+        [Fact]
+        public void TestPropertyPatternFactoryAndProperties()
+        {
+            var node = GeneratePropertyPattern();
+            
+            Assert.Null(node.Type);
+            Assert.NotNull(node.PropertySubpattern);
+            Assert.Null(node.Designation);
+            
+            AttachAndCheckDiagnostics(node);
+        }
+        
+        [Fact]
+        public void TestPropertySubpatternFactoryAndProperties()
+        {
+            var node = GeneratePropertySubpattern();
+            
+            Assert.Equal(SyntaxKind.OpenBraceToken, node.OpenBraceToken.Kind);
+            Assert.NotNull(node.SubPatterns);
+            Assert.Equal(SyntaxKind.CloseBraceToken, node.CloseBraceToken.Kind);
+            
+            AttachAndCheckDiagnostics(node);
+        }
+        
         [Fact]
         public void TestConstantPatternFactoryAndProperties()
         {
@@ -5543,6 +5613,110 @@ public void TestDeclarationPatternIdentityRewriter()
             Assert.Same(oldNode, newNode);
         }
         
+        [Fact]
+        public void TestDeconstructionPatternTokenDeleteRewriter()
+        {
+            var oldNode = GenerateDeconstructionPattern();
+            var rewriter = new TokenDeleteRewriter();
+            var newNode = rewriter.Visit(oldNode);
+            
+            if(!oldNode.IsMissing)
+            {
+                Assert.NotEqual(oldNode, newNode);
+            }
+            
+            Assert.NotNull(newNode);
+            Assert.True(newNode.IsMissing, "No tokens => missing");
+        }
+        
+        [Fact]
+        public void TestDeconstructionPatternIdentityRewriter()
+        {
+            var oldNode = GenerateDeconstructionPattern();
+            var rewriter = new IdentityRewriter();
+            var newNode = rewriter.Visit(oldNode);
+            
+            Assert.Same(oldNode, newNode);
+        }
+        
+        [Fact]
+        public void TestSubpatternElementTokenDeleteRewriter()
+        {
+            var oldNode = GenerateSubpatternElement();
+            var rewriter = new TokenDeleteRewriter();
+            var newNode = rewriter.Visit(oldNode);
+            
+            if(!oldNode.IsMissing)
+            {
+                Assert.NotEqual(oldNode, newNode);
+            }
+            
+            Assert.NotNull(newNode);
+            Assert.True(newNode.IsMissing, "No tokens => missing");
+        }
+        
+        [Fact]
+        public void TestSubpatternElementIdentityRewriter()
+        {
+            var oldNode = GenerateSubpatternElement();
+            var rewriter = new IdentityRewriter();
+            var newNode = rewriter.Visit(oldNode);
+            
+            Assert.Same(oldNode, newNode);
+        }
+        
+        [Fact]
+        public void TestPropertyPatternTokenDeleteRewriter()
+        {
+            var oldNode = GeneratePropertyPattern();
+            var rewriter = new TokenDeleteRewriter();
+            var newNode = rewriter.Visit(oldNode);
+            
+            if(!oldNode.IsMissing)
+            {
+                Assert.NotEqual(oldNode, newNode);
+            }
+            
+            Assert.NotNull(newNode);
+            Assert.True(newNode.IsMissing, "No tokens => missing");
+        }
+        
+        [Fact]
+        public void TestPropertyPatternIdentityRewriter()
+        {
+            var oldNode = GeneratePropertyPattern();
+            var rewriter = new IdentityRewriter();
+            var newNode = rewriter.Visit(oldNode);
+            
+            Assert.Same(oldNode, newNode);
+        }
+        
+        [Fact]
+        public void TestPropertySubpatternTokenDeleteRewriter()
+        {
+            var oldNode = GeneratePropertySubpattern();
+            var rewriter = new TokenDeleteRewriter();
+            var newNode = rewriter.Visit(oldNode);
+            
+            if(!oldNode.IsMissing)
+            {
+                Assert.NotEqual(oldNode, newNode);
+            }
+            
+            Assert.NotNull(newNode);
+            Assert.True(newNode.IsMissing, "No tokens => missing");
+        }
+        
+        [Fact]
+        public void TestPropertySubpatternIdentityRewriter()
+        {
+            var oldNode = GeneratePropertySubpattern();
+            var rewriter = new IdentityRewriter();
+            var newNode = rewriter.Visit(oldNode);
+            
+            Assert.Same(oldNode, newNode);
+        }
+        
         [Fact]
         public void TestConstantPatternTokenDeleteRewriter()
         {
@@ -9298,6 +9472,26 @@ private static DeclarationPatternSyntax GenerateDeclarationPattern()
             return SyntaxFactory.DeclarationPattern(GenerateIdentifierName(), GenerateSingleVariableDesignation());
         }
         
+        private static DeconstructionPatternSyntax GenerateDeconstructionPattern()
+        {
+            return SyntaxFactory.DeconstructionPattern(default(TypeSyntax), SyntaxFactory.Token(SyntaxKind.OpenParenToken), new SeparatedSyntaxList<SubpatternElementSyntax>(), SyntaxFactory.Token(SyntaxKind.CloseParenToken), default(PropertySubpatternSyntax), default(VariableDesignationSyntax));
+        }
+        
+        private static SubpatternElementSyntax GenerateSubpatternElement()
+        {
+            return SyntaxFactory.SubpatternElement(default(NameColonSyntax), GenerateDeclarationPattern());
+        }
+        
+        private static PropertyPatternSyntax GeneratePropertyPattern()
+        {
+            return SyntaxFactory.PropertyPattern(default(TypeSyntax), GeneratePropertySubpattern(), default(VariableDesignationSyntax));
+        }
+        
+        private static PropertySubpatternSyntax GeneratePropertySubpattern()
+        {
+            return SyntaxFactory.PropertySubpattern(SyntaxFactory.Token(SyntaxKind.OpenBraceToken), new SeparatedSyntaxList<SubpatternElementSyntax>(), SyntaxFactory.Token(SyntaxKind.CloseBraceToken));
+        }
+        
         private static ConstantPatternSyntax GenerateConstantPattern()
         {
             return SyntaxFactory.ConstantPattern(GenerateIdentifierName());
@@ -10825,6 +11019,56 @@ public void TestDeclarationPatternFactoryAndProperties()
             Assert.Equal(node, newNode);
         }
         
+        [Fact]
+        public void TestDeconstructionPatternFactoryAndProperties()
+        {
+            var node = GenerateDeconstructionPattern();
+            
+            Assert.Null(node.Type);
+            Assert.Equal(SyntaxKind.OpenParenToken, node.OpenParenToken.Kind());
+            Assert.NotNull(node.SubPatterns);
+            Assert.Equal(SyntaxKind.CloseParenToken, node.CloseParenToken.Kind());
+            Assert.Null(node.PropertySubpattern);
+            Assert.Null(node.Designation);
+            var newNode = node.WithType(node.Type).WithOpenParenToken(node.OpenParenToken).WithSubPatterns(node.SubPatterns).WithCloseParenToken(node.CloseParenToken).WithPropertySubpattern(node.PropertySubpattern).WithDesignation(node.Designation);
+            Assert.Equal(node, newNode);
+        }
+        
+        [Fact]
+        public void TestSubpatternElementFactoryAndProperties()
+        {
+            var node = GenerateSubpatternElement();
+            
+            Assert.Null(node.NameColon);
+            Assert.NotNull(node.Pattern);
+            var newNode = node.WithNameColon(node.NameColon).WithPattern(node.Pattern);
+            Assert.Equal(node, newNode);
+        }
+        
+        [Fact]
+        public void TestPropertyPatternFactoryAndProperties()
+        {
+            var node = GeneratePropertyPattern();
+            
+            Assert.Null(node.Type);
+            Assert.NotNull(node.PropertySubpattern);
+            Assert.Null(node.Designation);
+            var newNode = node.WithType(node.Type).WithPropertySubpattern(node.PropertySubpattern).WithDesignation(node.Designation);
+            Assert.Equal(node, newNode);
+        }
+        
+        [Fact]
+        public void TestPropertySubpatternFactoryAndProperties()
+        {
+            var node = GeneratePropertySubpattern();
+            
+            Assert.Equal(SyntaxKind.OpenBraceToken, node.OpenBraceToken.Kind());
+            Assert.NotNull(node.SubPatterns);
+            Assert.Equal(SyntaxKind.CloseBraceToken, node.CloseBraceToken.Kind());
+            var newNode = node.WithOpenBraceToken(node.OpenBraceToken).WithSubPatterns(node.SubPatterns).WithCloseBraceToken(node.CloseBraceToken);
+            Assert.Equal(node, newNode);
+        }
+        
         [Fact]
         public void TestConstantPatternFactoryAndProperties()
         {
@@ -14462,6 +14706,110 @@ public void TestDeclarationPatternIdentityRewriter()
             Assert.Same(oldNode, newNode);
         }
         
+        [Fact]
+        public void TestDeconstructionPatternTokenDeleteRewriter()
+        {
+            var oldNode = GenerateDeconstructionPattern();
+            var rewriter = new TokenDeleteRewriter();
+            var newNode = rewriter.Visit(oldNode);
+            
+            if(!oldNode.IsMissing)
+            {
+                Assert.NotEqual(oldNode, newNode);
+            }
+            
+            Assert.NotNull(newNode);
+            Assert.True(newNode.IsMissing, "No tokens => missing");
+        }
+        
+        [Fact]
+        public void TestDeconstructionPatternIdentityRewriter()
+        {
+            var oldNode = GenerateDeconstructionPattern();
+            var rewriter = new IdentityRewriter();
+            var newNode = rewriter.Visit(oldNode);
+            
+            Assert.Same(oldNode, newNode);
+        }
+        
+        [Fact]
+        public void TestSubpatternElementTokenDeleteRewriter()
+        {
+            var oldNode = GenerateSubpatternElement();
+            var rewriter = new TokenDeleteRewriter();
+            var newNode = rewriter.Visit(oldNode);
+            
+            if(!oldNode.IsMissing)
+            {
+                Assert.NotEqual(oldNode, newNode);
+            }
+            
+            Assert.NotNull(newNode);
+            Assert.True(newNode.IsMissing, "No tokens => missing");
+        }
+        
+        [Fact]
+        public void TestSubpatternElementIdentityRewriter()
+        {
+            var oldNode = GenerateSubpatternElement();
+            var rewriter = new IdentityRewriter();
+            var newNode = rewriter.Visit(oldNode);
+            
+            Assert.Same(oldNode, newNode);
+        }
+        
+        [Fact]
+        public void TestPropertyPatternTokenDeleteRewriter()
+        {
+            var oldNode = GeneratePropertyPattern();
+            var rewriter = new TokenDeleteRewriter();
+            var newNode = rewriter.Visit(oldNode);
+            
+            if(!oldNode.IsMissing)
+            {
+                Assert.NotEqual(oldNode, newNode);
+            }
+            
+            Assert.NotNull(newNode);
+            Assert.True(newNode.IsMissing, "No tokens => missing");
+        }
+        
+        [Fact]
+        public void TestPropertyPatternIdentityRewriter()
+        {
+            var oldNode = GeneratePropertyPattern();
+            var rewriter = new IdentityRewriter();
+            var newNode = rewriter.Visit(oldNode);
+            
+            Assert.Same(oldNode, newNode);
+        }
+        
+        [Fact]
+        public void TestPropertySubpatternTokenDeleteRewriter()
+        {
+            var oldNode = GeneratePropertySubpattern();
+            var rewriter = new TokenDeleteRewriter();
+            var newNode = rewriter.Visit(oldNode);
+            
+            if(!oldNode.IsMissing)
+            {
+                Assert.NotEqual(oldNode, newNode);
+            }
+            
+            Assert.NotNull(newNode);
+            Assert.True(newNode.IsMissing, "No tokens => missing");
+        }
+        
+        [Fact]
+        public void TestPropertySubpatternIdentityRewriter()
+        {
+            var oldNode = GeneratePropertySubpattern();
+            var rewriter = new IdentityRewriter();
+            var newNode = rewriter.Visit(oldNode);
+            
+            Assert.Same(oldNode, newNode);
+        }
+        
         [Fact]
         public void TestConstantPatternTokenDeleteRewriter()
         {

src/Test/Utilities/Portable/TestResource.resx

@@ -324,6 +324,8 @@ namespace My
                     break;
                 case int i:
                     break;
+                case Type (int x, 3) { A: 5, B: 7 } identifier:
+                    break;
                 default:
                     {
                         return;