Use Compiltation to thread through nullability

The work for generic `unmanaged struct` constraints ended up threading
through the correct `Compilation` object in many of the cases where I
was using `Compilation` to calculate whether or not nullability needed
to be checked for constraints. Used that whenever possible.

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

@@ -578,7 +578,6 @@ private void Validate()
 
             var corLibrary = _compilation.SourceAssembly.CorLibrary;
             var conversions = new TypeConversions(corLibrary);
-            bool includeNullability = _compilation.IsFeatureEnabled(MessageID.IDS_FeatureNullableReferenceTypes);
             foreach (var @using in Usings)
             {
                 // Check if `using static` directives meet constraints.
@@ -586,7 +585,7 @@ private void Validate()
                 {
                     var typeSymbol = (TypeSymbol)@using.NamespaceOrType;
                     var location = @using.UsingDirective?.Name.Location ?? NoLocation.Singleton;
-                    typeSymbol.CheckAllConstraints(_compilation, conversions, includeNullability, location, semanticDiagnostics);
+                    typeSymbol.CheckAllConstraints(_compilation, conversions, location, semanticDiagnostics);
                 }
             }
 

src/Compilers/CSharp/Portable/Binder/Semantics/OverloadResolution/OverloadResolution.cs

@@ -3189,7 +3189,7 @@ internal EffectiveParameters(ImmutableArray<TypeSymbolWithAnnotations> types, Im
                     var parameterTypes = leastOverriddenMember.GetParameterTypes();
                     for (int i = 0; i < parameterTypes.Length; i++)
                     {
-                        if (!parameterTypes[i].TypeSymbol.CheckAllConstraints(Compilation, Conversions, Conversions.IncludeNullability))
+                        if (!parameterTypes[i].TypeSymbol.CheckAllConstraints(Compilation, Conversions))
                         {
                             return new MemberResolutionResult<TMember>(member, leastOverriddenMember, MemberAnalysisResult.ConstructedParameterFailedConstraintsCheck(i));
                         }

src/Compilers/CSharp/Portable/Binder/Semantics/OverloadResolution/OverloadResolutionResult.cs

@@ -974,7 +974,7 @@ private void ReportDuplicateNamedArgument(MemberResolutionResult<TMember> result
             // formal parameter type.
 
             TypeSymbol formalParameterType = method.ParameterTypes[result.Result.BadParameter].TypeSymbol;
-            formalParameterType.CheckAllConstraints((CSharpCompilation)compilation, conversions.IncludeNullability, conversions, location, diagnostics);
+            formalParameterType.CheckAllConstraints((CSharpCompilation)compilation, conversions, conversions.IncludeNullability, location, diagnostics);
 
             return true;
         }

src/Compilers/CSharp/Portable/Symbols/AliasSymbol.cs

@@ -304,8 +304,7 @@ internal void CheckConstraints(DiagnosticBag diagnostics)
             {
                 var corLibrary = this.ContainingAssembly.CorLibrary;
                 var conversions = new TypeConversions(corLibrary);
-                bool includeNullability = DeclaringCompilation.IsFeatureEnabled(MessageID.IDS_FeatureNullableReferenceTypes);
-                target.CheckAllConstraints(DeclaringCompilation, conversions, includeNullability, _locations[0], diagnostics);
+                target.CheckAllConstraints(DeclaringCompilation, conversions, _locations[0], diagnostics);
             }
         }
 

src/Compilers/CSharp/Portable/Symbols/ConstraintsHelper.cs

@@ -459,26 +459,39 @@ internal static class ConstraintsHelper
             this TypeSymbol type,
             CSharpCompilation compilation,
             ConversionsBase conversions,
-            bool includeNullability,
             Location location,
             DiagnosticBag diagnostics)
         {
-            type.VisitType(s_checkConstraintsSingleTypeFunc, new CheckConstraintsArgs(compilation, conversions, includeNullability, location, diagnostics));
+            bool includeNullability = compilation.IsFeatureEnabled(MessageID.IDS_FeatureNullableReferenceTypes);
+            CheckAllConstraints(type, compilation, conversions, includeNullability, location, diagnostics);
         }
 
         public static bool CheckAllConstraints(
             this TypeSymbol type,
             CSharpCompilation compilation,
-            ConversionsBase conversions,
-            bool includeNullability)
+            ConversionsBase conversions)
         {
             var diagnostics = DiagnosticBag.GetInstance();
-            type.CheckAllConstraints(compilation, conversions, includeNullability, NoLocation.Singleton, diagnostics);
+
+            // Nullability checks can only add warnings here so skip them for this check as we are only
+            // concerned with errors.
+            CheckAllConstraints(type, compilation, conversions, includeNullability: false, NoLocation.Singleton, diagnostics);
             bool ok = !diagnostics.HasAnyErrors();
             diagnostics.Free();
             return ok;
         }
 
+        public static void CheckAllConstraints(
+            this TypeSymbol type,
+            CSharpCompilation compilation,
+            ConversionsBase conversions,
+            bool includeNullability,
+            Location location,
+            DiagnosticBag diagnostics)
+        {
+            type.VisitType(s_checkConstraintsSingleTypeFunc, new CheckConstraintsArgs(compilation, conversions, includeNullability, location, diagnostics));
+        }
+
         private readonly struct CheckConstraintsArgs
         {
             public readonly CSharpCompilation CurrentCompilation;

src/Compilers/CSharp/Portable/Symbols/Source/SourceCustomEventSymbol.cs

@@ -183,7 +183,7 @@ internal override void AfterAddingTypeMembersChecks(ConversionsBase conversions,
             {
                 var explicitInterfaceSpecifier = this.ExplicitInterfaceSpecifier;
                 Debug.Assert(explicitInterfaceSpecifier != null);
-                _explicitInterfaceType.CheckAllConstraints(DeclaringCompilation, conversions, includeNullability, new SourceLocation(explicitInterfaceSpecifier.Name), diagnostics);
+                _explicitInterfaceType.CheckAllConstraints(DeclaringCompilation, conversions, new SourceLocation(explicitInterfaceSpecifier.Name), diagnostics);
             }
 
             if (!_explicitInterfaceImplementations.IsEmpty)

src/Compilers/CSharp/Portable/Symbols/Source/SourceEventSymbol.cs

@@ -671,7 +671,7 @@ internal override void AfterAddingTypeMembersChecks(ConversionsBase conversions,
             bool includeNullability = DeclaringCompilation.IsFeatureEnabled(MessageID.IDS_FeatureNullableReferenceTypes);
 
             this.CheckModifiersAndType(diagnostics);
-            this.Type.CheckAllConstraints(DeclaringCompilation, conversions, includeNullablity, location, diagnostics);
+            this.Type.CheckAllConstraints(DeclaringCompilation, conversions, location, diagnostics);
 
             if (this.Type.NeedsNullableAttribute())
             {

src/Compilers/CSharp/Portable/Symbols/Source/SourceMemberFieldSymbol.cs

@@ -575,8 +575,7 @@ internal override bool IsDefinedInSourceTree(SyntaxTree tree, TextSpan? definedW
         internal override void AfterAddingTypeMembersChecks(ConversionsBase conversions, DiagnosticBag diagnostics)
         {
             var options = (CSharpParseOptions)SyntaxTree.Options;
-            bool includeNullability = options.IsFeatureEnabled(MessageID.IDS_FeatureNullableReferenceTypes);
-            Type.CheckAllConstraints(DeclaringCompilation, conversions, includeNullability, ErrorLocation, diagnostics);
+            Type.CheckAllConstraints(DeclaringCompilation, conversions, ErrorLocation, diagnostics);
             base.AfterAddingTypeMembersChecks(conversions, diagnostics);
         }
     }

src/Compilers/CSharp/Portable/Symbols/Source/SourceNamedTypeSymbol_Bases.cs

@@ -106,8 +106,7 @@ protected override void CheckBase(DiagnosticBag diagnostics)
                 var corLibrary = this.ContainingAssembly.CorLibrary;
                 var conversions = new TypeConversions(corLibrary);
                 var location = singleDeclaration.NameLocation;
-                bool includeNullability = DeclaringCompilation.IsFeatureEnabled(MessageID.IDS_FeatureNullableReferenceTypes);
-                localBase.CheckAllConstraints(DeclaringCompilation, conversions, includeNullability, location, diagnostics);
+                localBase.CheckAllConstraints(DeclaringCompilation, conversions, location, diagnostics);
             }
         }
 
@@ -132,7 +131,6 @@ protected override void CheckInterfaces(DiagnosticBag diagnostics)
                 var corLibrary = this.ContainingAssembly.CorLibrary;
                 var conversions = new TypeConversions(corLibrary);
                 var location = singleDeclaration.NameLocation;
-                bool includeNullability = DeclaringCompilation.IsFeatureEnabled(MessageID.IDS_FeatureNullableReferenceTypes);
 
                 foreach (var pair in interfaces)
                 {
@@ -140,11 +138,7 @@ protected override void CheckInterfaces(DiagnosticBag diagnostics)
 
                     foreach (var @interface in set)
                     {
-<<<<<<< HEAD
                         @interface.CheckAllConstraints(DeclaringCompilation, conversions, location, diagnostics);
-=======
-                        @interface.CheckAllConstraints(conversions, includeNullability, location, diagnostics);
->>>>>>> Make nullability explicit constraint parameter
                     }
 
                     if (set.Count > 1)

src/Compilers/CSharp/Portable/Symbols/Source/SourceOrdinaryMethodSymbol.cs

@@ -1010,7 +1010,6 @@ internal override void ForceComplete(SourceLocation locationOpt, CancellationTok
         internal override void AfterAddingTypeMembersChecks(ConversionsBase conversions, DiagnosticBag diagnostics)
         {
             var location = GetSyntax().ReturnType.Location;
-            bool includeNullability = DeclaringCompilation.IsFeatureEnabled(MessageID.IDS_FeatureNullableReferenceTypes);
 
             Debug.Assert(location != null);
 
@@ -1022,14 +1021,14 @@ internal override void AfterAddingTypeMembersChecks(ConversionsBase conversions,
             {
                 var syntax = this.GetSyntax();
                 Debug.Assert(syntax.ExplicitInterfaceSpecifier != null);
-                _explicitInterfaceType.CheckAllConstraints(DeclaringCompilation, conversions, includeNullability, new SourceLocation(syntax.ExplicitInterfaceSpecifier.Name), diagnostics);
+                _explicitInterfaceType.CheckAllConstraints(DeclaringCompilation, conversions, new SourceLocation(syntax.ExplicitInterfaceSpecifier.Name), diagnostics);
             }
 
-            this.ReturnType.CheckAllConstraints(DeclaringCompilation, conversions, includeNullability, this.Locations[0], diagnostics);
+            this.ReturnType.CheckAllConstraints(DeclaringCompilation, conversions, this.Locations[0], diagnostics);
 
             foreach (var parameter in this.Parameters)
             {
-                parameter.Type.CheckAllConstraints(DeclaringCompilation, conversions, includeNullability, parameter.Locations[0], diagnostics);
+                parameter.Type.CheckAllConstraints(DeclaringCompilation, conversions, parameter.Locations[0], diagnostics);
             }
 
             var implementingPart = this.SourcePartialImplementation;

src/Compilers/CSharp/Portable/Symbols/Source/SourcePropertySymbol.cs

@@ -742,9 +742,8 @@ internal override void AfterAddingTypeMembersChecks(ConversionsBase conversions,
             if ((object)_explicitInterfaceType != null)
             {
                 var explicitInterfaceSpecifier = GetExplicitInterfaceSpecifier(this.CSharpSyntaxNode);
-                bool includeNullability = DeclaringCompilation.IsFeatureEnabled(MessageID.IDS_FeatureNullableReferenceTypes);
                 Debug.Assert(explicitInterfaceSpecifier != null);
-                _explicitInterfaceType.CheckAllConstraints(DeclaringCompilation, conversions, includeNullability, new SourceLocation(explicitInterfaceSpecifier.Name), diagnostics);
+                _explicitInterfaceType.CheckAllConstraints(DeclaringCompilation, conversions, new SourceLocation(explicitInterfaceSpecifier.Name), diagnostics);
 
                 // Note: we delayed nullable-related checks that could pull on NonNullTypes
                 PropertySymbol overriddenOrImplementedProperty = null;
@@ -1380,11 +1379,10 @@ internal override void ForceComplete(SourceLocation locationOpt, CancellationTok
                                 {
                                     var diagnostics = DiagnosticBag.GetInstance();
                                     var conversions = new TypeConversions(this.ContainingAssembly.CorLibrary);
-                                    bool includeNullability = DeclaringCompilation.IsFeatureEnabled(MessageID.IDS_FeatureNullableReferenceTypes);
                                     foreach (var parameter in this.Parameters)
                                     {
                                         parameter.ForceComplete(locationOpt, cancellationToken);
-                                        parameter.Type.CheckAllConstraints(DeclaringCompilation, conversions, includeNullability, parameter.Locations[0], diagnostics);
+                                        parameter.Type.CheckAllConstraints(DeclaringCompilation, conversions, parameter.Locations[0], diagnostics);
                                     }
 
                                     this.AddDeclarationDiagnostics(diagnostics);
@@ -1411,7 +1409,7 @@ internal override void ForceComplete(SourceLocation locationOpt, CancellationTok
                                 var diagnostics = DiagnosticBag.GetInstance();
                                 var conversions = new TypeConversions(this.ContainingAssembly.CorLibrary);
                                 bool includeNullability = DeclaringCompilation.IsFeatureEnabled(MessageID.IDS_FeatureNullableReferenceTypes);
-                                this.Type.CheckAllConstraints(DeclaringCompilation, conversions, includeNullability, _location, diagnostics);
+                                this.Type.CheckAllConstraints(DeclaringCompilation, conversions, _location, diagnostics);
 
                                 var type = this.Type.TypeSymbol;
                                 if (type.IsRestrictedType(ignoreSpanLikeTypes: true))

src/Compilers/CSharp/Portable/Symbols/Source/SourceTypeParameterSymbol.cs

@@ -261,7 +261,6 @@ private void CheckConstraintTypeConstraints(DiagnosticBag diagnostics)
 
             var corLibrary = this.ContainingAssembly.CorLibrary;
             var conversions = new TypeConversions(corLibrary);
-            bool includeNullability = DeclaringCompilation.IsFeatureEnabled(MessageID.IDS_FeatureNullableReferenceTypes);
             var location = _locations[0];
 
             foreach (var constraintType in constraintTypes)
@@ -271,7 +270,7 @@ private void CheckConstraintTypeConstraints(DiagnosticBag diagnostics)
 
                 if (!diagnostics.Add(location, useSiteDiagnostics))
                 {
-                    constraintType.CheckAllConstraints(DeclaringCompilation, conversions, includeNullability, location, diagnostics);
+                    constraintType.CheckAllConstraints(DeclaringCompilation, conversions, location, diagnostics);
                 }
             }
         }

src/Compilers/CSharp/Portable/Symbols/Source/SourceUserDefinedOperatorSymbolBase.cs

@@ -644,12 +644,11 @@ internal sealed override void AfterAddingTypeMembersChecks(ConversionsBase conve
             // method name location for any such errors. We'll do the same for return
             // type errors but for parameter errors, we'll use the parameter location.
 
-            bool includeNullability = DeclaringCompilation.IsFeatureEnabled(MessageID.IDS_FeatureNullableReferenceTypes);
-            this.ReturnType.CheckAllConstraints(DeclaringCompilation, conversions, includeNullability, this.Locations[0], diagnostics);
+            this.ReturnType.CheckAllConstraints(DeclaringCompilation, conversions, this.Locations[0], diagnostics);
 
             foreach (var parameter in this.Parameters)
             {
-                parameter.Type.CheckAllConstraints(DeclaringCompilation, conversions, includeNullability, parameter.Locations[0], diagnostics);
+                parameter.Type.CheckAllConstraints(DeclaringCompilation, conversions, parameter.Locations[0], diagnostics);
             }
 
             ParameterHelpers.EnsureIsReadOnlyAttributeExists(Parameters, diagnostics, modifyCompilation: true);

src/Compilers/CSharp/Portable/Symbols/TypeParameterSymbol.cs

@@ -584,7 +584,7 @@ internal bool GetIsValueType(ConsList<TypeParameterSymbol> inProgress)
         }
 
         public sealed override bool IsValueType => GetIsValueType(ConsList<TypeParameterSymbol>.Empty);
-        
+
         internal sealed override ManagedKind ManagedKind
         {
             get

src/Compilers/CSharp/Portable/Symbols/TypeSymbolWithAnnotations.cs

@@ -730,9 +730,9 @@ public bool GetUnificationUseSiteDiagnosticRecursive(ref DiagnosticInfo result,
                    Symbol.GetUnificationUseSiteDiagnosticRecursive(ref result, this.CustomModifiers, owner, ref checkedTypes);
         }
 
-        public void CheckAllConstraints(CSharpCompilation compilation, ConversionsBase conversions, bool includeNullability, Location location, DiagnosticBag diagnostics)
+        public void CheckAllConstraints(CSharpCompilation compilation, ConversionsBase conversions, Location location, DiagnosticBag diagnostics)
         {
-            TypeSymbol.CheckAllConstraints(compilation, conversions, includeNullability, location, diagnostics);
+            TypeSymbol.CheckAllConstraints(compilation, conversions, location, diagnostics);
         }
 
         public bool IsAtLeastAsVisibleAs(Symbol sym, ref HashSet<DiagnosticInfo> useSiteDiagnostics)

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

@@ -57031,10 +57031,7 @@ class B4 : A<string?>
             comp.VerifyDiagnostics(
                 // (11,20): warning CS8632: The annotation for nullable reference types should only be used in code within a '#nullable' context.
                 // class B2 : A<string?>
-                Diagnostic(ErrorCode.WRN_MissingNonNullTypesContextForAnnotation, "?").WithLocation(11, 20),
-                // (27,7): warning CS8634: The type 'string?' cannot be used as type parameter 'T' in the generic type or method 'A<T>'. Nullability of type argument 'string?' doesn't match 'class' constraint.
-                // class B4 : A<string?>
-                Diagnostic(ErrorCode.WRN_NullabilityMismatchInTypeParameterReferenceTypeConstraint, "B4").WithArguments("A<T>", "T", "string?").WithLocation(27, 7)
+                Diagnostic(ErrorCode.WRN_MissingNonNullTypesContextForAnnotation, "?").WithLocation(11, 20)
                 );
             verifyAllConstraintTypes();
 
@@ -57063,7 +57060,10 @@ class B4 : A<string?>
             comp.VerifyDiagnostics(
                 // (11,20): warning CS8632: The annotation for nullable reference types should only be used in code within a '#nullable' context.
                 // class B2 : A<string?>
-                Diagnostic(ErrorCode.WRN_MissingNonNullTypesContextForAnnotation, "?").WithLocation(11, 20)
+                Diagnostic(ErrorCode.WRN_MissingNonNullTypesContextForAnnotation, "?").WithLocation(11, 20),
+                // (27,7): warning CS8634: The type 'string?' cannot be used as type parameter 'T' in the generic type or method 'A<T>'. Nullability of type argument 'string?' doesn't match 'class' constraint.
+                // class B4 : A<string?>
+                Diagnostic(ErrorCode.WRN_NullabilityMismatchInTypeParameterReferenceTypeConstraint, "B4").WithArguments("A<T>", "T", "string?").WithLocation(27, 7)
                 );
             verifyAllConstraintTypes();