fixup after merge

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

@@ -672,7 +672,7 @@ private bool CheckEventValueKind(BoundEventAccess boundEvent, BindValueKind valu
                         return false;
                     }
                     else if (RequiresVariableReceiver(receiver, eventSymbol.AssociatedField) && // NOTE: using field, not event
-                        !CheckIsValidReceiverForVariable(eventSyntax, receiver, BindValueKind.Assignable, diagnostics))
+                        !CheckIsValidReceiverForVariable(eventSyntax, receiver, valueKind, diagnostics))
                     {
                         return false;
                     }

src/Compilers/CSharp/Portable/CommandLine/CSharpCommandLineParser.cs

@@ -1544,51 +1544,6 @@ public static IEnumerable<string> ParseConditionalCompilationSymbols(string valu
             return defines.AsEnumerable();
         }
 
-        public static bool TryParseLanguageVersion(string value, out LanguageVersion version)
-        {
-            if (value == null)
-            {
-                version = LanguageVersion.Default;
-                return true;
-            }
-
-            switch (value.ToLowerInvariant())
-            {
-                case "iso-1":
-                    version = LanguageVersion.CSharp1;
-                    return true;
-
-                case "iso-2":
-                    version = LanguageVersion.CSharp2;
-                    return true;
-
-                case "default":
-                    version = LanguageVersion.Default;
-                    return true;
-
-                case "latest":
-                    version = LanguageVersion.Latest;
-                    return true;
-
-                case "7.1":
-                    version = LanguageVersion.CSharp7_1;
-                    return true;
-
-                default:
-                    if (int.TryParse(value, NumberStyles.None, CultureInfo.InvariantCulture, out int versionNumber))
-                    {
-                        version = (LanguageVersion)versionNumber;
-                        if (version.IsValid())
-                        {
-                            return true;
-                        }
-                    }
-
-                    version = LanguageVersion.Default;
-                    return false;
-            }
-        }
-
         private static Platform ParsePlatform(string value, IList<Diagnostic> diagnostics)
         {
             switch (value.ToLowerInvariant())

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

-Microsoft.CodeAnalysis.CSharp.LanguageVersion.CSharp7_2 = 702 -> Microsoft.CodeAnalysis.CSharp.LanguageVersion
\ No newline at end of file
+Microsoft.CodeAnalysis.CSharp.LanguageVersion.CSharp7_2 = 702 -> Microsoft.CodeAnalysis.CSharp.LanguageVersion
+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
+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

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

@@ -386,7 +386,7 @@ private sealed class EndInvokeMethod : SourceDelegateMethodSymbol
                 InitializeParameters(parameters.ToImmutableAndFree());
             }
 
-            protected override SourceMethodSymbol BoundAttributesSource => _invoke;
+            protected override SourceMemberMethodSymbol BoundAttributesSource => _invoke;
 
             public override string Name => WellKnownMemberNames.DelegateEndInvokeName;
 

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

@@ -254,7 +254,7 @@ private DeclarationModifiers MakeModifiers(TypeKind typeKind, DiagnosticBag diag
                     allowedModifiers |= DeclarationModifiers.Partial | DeclarationModifiers.Static | DeclarationModifiers.Sealed | DeclarationModifiers.Abstract | DeclarationModifiers.Unsafe;
                     break;
                 case TypeKind.Struct:
-                    allowedModifiers |= DeclarationModifiers.Ref | DeclarationModifiers.ReadOnly | DeclarationModifiers.Unsafe;
+                    allowedModifiers |= DeclarationModifiers.Partial | DeclarationModifiers.Ref | DeclarationModifiers.ReadOnly | DeclarationModifiers.Unsafe;
                     break;
                 case TypeKind.Interface:
                     allowedModifiers |= DeclarationModifiers.Partial | DeclarationModifiers.Unsafe;

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

@@ -1430,13 +1430,6 @@ public sealed override bool HidesBaseMethodsByName
             {
                 return false;
             }
-
-            if (_refKind == RefKind.RefReadOnly)
-            {
-                this.DeclaringCompilation.EnsureIsReadOnlyAttributeExists(diagnostics, GetSyntax().ReturnType.Location, modifyCompilationForRefReadOnly: true);
-            }
-
-            ParameterHelpers.EnsureIsReadOnlyAttributeExists(Parameters, diagnostics, modifyCompilationForRefReadOnly: true);
         }
 
         internal override bool HasRuntimeSpecialName

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

@@ -148,10 +148,10 @@ interface I1
                 // (43,9): error CS1604: Cannot assign to 'this' because it is read-only
                 //         e = () => { };
                 Diagnostic(ErrorCode.ERR_AssgReadonlyLocal, "e").WithArguments("this").WithLocation(43, 9),
-                // (46,16): error CS1604: Cannot assign to 'this' because it is read-only
+                // (46,16): error CS1605: Cannot use 'this' as a ref or out value because it is read-only
                 //         M1(ref e);
-                Diagnostic(ErrorCode.ERR_AssgReadonlyLocal, "e").WithArguments("this").WithLocation(46, 16)
-    );
+                Diagnostic(ErrorCode.ERR_RefReadonlyLocal, "e").WithArguments("this").WithLocation(46, 16)
+            );
         }
 
         private static string ilreadonlyStructWithWriteableFieldIL = @"

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

@@ -629,9 +629,9 @@ public class C
                 // (46,32): error CS8168: Cannot return local 'M2' by reference because it is not a ref local
                 //             return ref Goo(ref M2).x;
                 Diagnostic(ErrorCode.ERR_RefReturnLocal, "M2").WithArguments("M2").WithLocation(46, 32),
-                // (46,24): error CS8165: Cannot return by reference a member of result of 'Test.Foo<Test.S1>(ref Test.S1)' because the argument passed to parameter 'arg' cannot be returned by reference
-                //             return ref Foo(ref M2).x;
-                Diagnostic(ErrorCode.ERR_RefReturnCall2, "Foo(ref M2)").WithArguments("Test.Foo<Test.S1>(ref Test.S1)", "arg").WithLocation(46, 24),
+                // (46,24): error CS8165: Cannot return by reference a member of result of 'Test.Goo<Test.S1>(ref Test.S1)' because the argument passed to parameter 'arg' cannot be returned by reference
+                //             return ref Goo(ref M2).x;
+                Diagnostic(ErrorCode.ERR_RefReturnCall2, "Goo(ref M2)").WithArguments("Test.Goo<Test.S1>(ref Test.S1)", "arg").WithLocation(46, 24),
                 // (58,24): error CS8170: Struct members cannot return 'this' or other instance members by reference
                 //             return ref this;
                 Diagnostic(ErrorCode.ERR_RefReturnStructThis, "this").WithArguments("this").WithLocation(58, 24)
@@ -1885,9 +1885,10 @@ class Program
 ";
 
             CreateCompilationWithMscorlib46(text).VerifyDiagnostics(
-                // (8,20): error CS8160: A readonly field cannot be returned by reference
+                // (8,20): error CS0192: A readonly field cannot be used as a ref or out value (except in a constructor)
                 //         return ref i;
-                Diagnostic(ErrorCode.ERR_RefReturnReadonly, "i").WithLocation(8, 20));
+                Diagnostic(ErrorCode.ERR_RefReadonly, "i").WithLocation(8, 20)
+            );
         }
 
         [Fact]
@@ -2043,9 +2044,10 @@ class Program
 ";
 
             CreateCompilationWithMscorlib46(text).VerifyDiagnostics(
-                // (6,20): error CS1605: Cannot use 'this' as a ref or out value because it is read-only
+                // (6,20): error CS8170: Struct members cannot return 'this' or other instance members by reference
                 //         return ref this;
-                Diagnostic(ErrorCode.ERR_RefReadonlyLocal, "this").WithArguments("this").WithLocation(6, 20));
+                Diagnostic(ErrorCode.ERR_RefReturnStructThis, "this").WithArguments("this").WithLocation(6, 20)
+            );
         }
 
         [Fact]
@@ -2121,7 +2123,11 @@ class Program
             CreateCompilationWithMscorlib46(text).VerifyDiagnostics(
                 // (6,9): error CS8150: By-value returns may only be used in methods that return by value
                 //         return;
-                Diagnostic(ErrorCode.ERR_MustHaveRefReturn, "return").WithLocation(6, 9));
+                Diagnostic(ErrorCode.ERR_MustHaveRefReturn, "return").WithLocation(6, 9),
+                // (6,9): error CS0126: An object of a type convertible to 'int' is required
+                //         return;
+                Diagnostic(ErrorCode.ERR_RetObjectRequired, "return").WithArguments("int").WithLocation(6, 9)
+            );
         }
 
         [Fact]

src/Compilers/CSharp/Test/Symbol/Symbols/SymbolErrorTests.cs

@@ -11401,18 +11401,15 @@ public int RetInt(byte b, int k)
             var comp = CreateStandardCompilation(text);
 
             comp.VerifyDiagnostics(
-                // (7,14): error CS0663: 'IFoo<T>' cannot define an overloaded method that differ only on parameter modifiers 'out' and 'ref'
+                // (7,14): error CS0663: 'IGoo<T>' cannot define an overloaded method that differs only on parameter modifiers 'out' and 'ref'
                 //         void M(out T t);
-                Diagnostic(ErrorCode.ERR_OverloadRefKind, "M").WithArguments("NS.IFoo<T>", "method", "out", "ref").WithLocation(7, 14),
-                // (24,20): error CS0663: 'CFoo' cannot define an overloaded method that differ only on parameter modifiers 'ref' and 'out'
+                Diagnostic(ErrorCode.ERR_OverloadRefKind, "M").WithArguments("NS.IGoo<T>", "method", "out", "ref").WithLocation(7, 14),
+                // (24,20): error CS0663: 'CGoo' cannot define an overloaded method that differs only on parameter modifiers 'ref' and 'out'
                 //         public int RetInt(byte b, ref int j)
-                Diagnostic(ErrorCode.ERR_OverloadRefKind, "RetInt").WithArguments("NS.CFoo", "method", "ref", "out").WithLocation(24, 20),
-                // (16,18): error CS0663: 'CFoo.SFoo' cannot define an overloaded method that differ only on parameter modifiers 'out' and 'ref'
+                Diagnostic(ErrorCode.ERR_OverloadRefKind, "RetInt").WithArguments("NS.CGoo", "method", "ref", "out").WithLocation(24, 20),
+                // (16,18): error CS0663: 'CGoo.SGoo' cannot define an overloaded method that differs only on parameter modifiers 'out' and 'ref'
                 //             void M<T>(out T t) { }
-                Diagnostic(ErrorCode.ERR_OverloadRefKind, "M").WithArguments("NS.CFoo.SFoo", "method", "out", "ref").WithLocation(16, 18),
-
-                // Dev10 stops after reporting the overload problems.  However, it produces the errors below once those problems are fixed.
-
+                Diagnostic(ErrorCode.ERR_OverloadRefKind, "M").WithArguments("NS.CGoo.SGoo", "method", "out", "ref").WithLocation(16, 18),
                 // (21,20): error CS0269: Use of unassigned out parameter 'i'
                 //             return i;
                 Diagnostic(ErrorCode.ERR_UseDefViolationOut, "i").WithArguments("i").WithLocation(21, 20),
@@ -11421,7 +11418,8 @@ public int RetInt(byte b, int k)
                 Diagnostic(ErrorCode.ERR_ParamUnassigned, "return i;").WithArguments("i").WithLocation(21, 13),
                 // (16,18): error CS0177: The out parameter 't' must be assigned to before control leaves the current method
                 //             void M<T>(out T t) { }
-                Diagnostic(ErrorCode.ERR_ParamUnassigned, "M").WithArguments("t").WithLocation(16, 18));
+                Diagnostic(ErrorCode.ERR_ParamUnassigned, "M").WithArguments("t").WithLocation(16, 18)
+            );
         }
 
         [Fact]

src/Compilers/CSharp/Test/Syntax/Parsing/ParserErrorMessageTests.cs

@@ -4893,10 +4893,8 @@ void M()
             CreateStandardCompilation(test, options: new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary, allowUnsafe: true)).VerifyDiagnostics(
                 // (6,15): error CS0283: The type 'int*' cannot be declared const
                 //         const int* p = stackalloc int[1];
-                Diagnostic(ErrorCode.ERR_BadConstType, "int*").WithArguments("int*").WithLocation(6, 15),
-                // (6,24): error CS1525: Invalid expression term 'stackalloc'
-                //         const int* p = stackalloc int[1];
-                Diagnostic(ErrorCode.ERR_InvalidExprTerm, "stackalloc").WithArguments("stackalloc").WithLocation(6, 24));
+                Diagnostic(ErrorCode.ERR_BadConstType, "int*").WithArguments("int*").WithLocation(6, 15)
+            );
         }
         
         [Fact]
@@ -4936,9 +4934,13 @@ unsafe public static void Main()
 }
 ";
             CreateStandardCompilation(test, options: TestOptions.ReleaseDll.WithAllowUnsafe(true)).VerifyDiagnostics(
-                // (6,39): error CS0029: Cannot implicitly convert type 'int*' to 'System.IDisposable'
+                // (6,39): error CS0518: Predefined type 'System.Span`1' is not defined or imported
+                //         using (System.IDisposable v = stackalloc int[1])
+                Diagnostic(ErrorCode.ERR_PredefinedTypeNotFound, "stackalloc int[1]").WithArguments("System.Span`1").WithLocation(6, 39),
+                // (6,39): error CS8520: Conversion of a stackalloc expression of type 'int' to type 'IDisposable' is not possible.
                 //         using (System.IDisposable v = stackalloc int[1])
-                Diagnostic(ErrorCode.ERR_NoImplicitConv, "stackalloc int[1]").WithArguments("int*", "System.IDisposable").WithLocation(6, 39));
+                Diagnostic(ErrorCode.ERR_StackAllocConversionNotPossible, "stackalloc int[1]").WithArguments("int", "System.IDisposable").WithLocation(6, 39)
+             );
         }
 
         [WorkItem(906993, "DevDiv/Personal")]

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

@@ -33,6 +33,7 @@ Microsoft.CodeAnalysis.Diagnostics.Telemetry.AnalyzerTelemetryInfo.OperationBloc
 Microsoft.CodeAnalysis.Diagnostics.Telemetry.AnalyzerTelemetryInfo.OperationBlockEndActionsCount.set -> void
 Microsoft.CodeAnalysis.Diagnostics.Telemetry.AnalyzerTelemetryInfo.OperationBlockStartActionsCount.get -> int
 Microsoft.CodeAnalysis.Diagnostics.Telemetry.AnalyzerTelemetryInfo.OperationBlockStartActionsCount.set -> void
+Microsoft.CodeAnalysis.IMethodSymbol.ReturnsByRefReadonly.get -> bool
 Microsoft.CodeAnalysis.IOperation
 Microsoft.CodeAnalysis.IOperation.Accept(Microsoft.CodeAnalysis.Semantics.OperationVisitor visitor) -> void
 Microsoft.CodeAnalysis.IOperation.Accept<TArgument, TResult>(Microsoft.CodeAnalysis.Semantics.OperationVisitor<TArgument, TResult> visitor, TArgument argument) -> TResult
@@ -41,6 +42,7 @@ Microsoft.CodeAnalysis.IOperation.IsInvalid.get -> bool
 Microsoft.CodeAnalysis.IOperation.Kind.get -> Microsoft.CodeAnalysis.OperationKind
 Microsoft.CodeAnalysis.IOperation.Syntax.get -> Microsoft.CodeAnalysis.SyntaxNode
 Microsoft.CodeAnalysis.IOperation.Type.get -> Microsoft.CodeAnalysis.ITypeSymbol
+Microsoft.CodeAnalysis.IPropertySymbol.ReturnsByRefReadonly.get -> bool
 Microsoft.CodeAnalysis.OperationKind
 Microsoft.CodeAnalysis.OperationKind.AddressOfExpression = 515 -> Microsoft.CodeAnalysis.OperationKind
 Microsoft.CodeAnalysis.OperationKind.Argument = 1031 -> Microsoft.CodeAnalysis.OperationKind
@@ -118,6 +120,7 @@ Microsoft.CodeAnalysis.OperationKind.VariableDeclarationStatement = 3 -> Microso
 Microsoft.CodeAnalysis.OperationKind.WithStatement = 82 -> Microsoft.CodeAnalysis.OperationKind
 Microsoft.CodeAnalysis.OperationKind.YieldBreakStatement = 12 -> Microsoft.CodeAnalysis.OperationKind
 Microsoft.CodeAnalysis.OperationKind.YieldReturnStatement = 16 -> Microsoft.CodeAnalysis.OperationKind
+Microsoft.CodeAnalysis.RefKind.RefReadOnly = 3 -> Microsoft.CodeAnalysis.RefKind
 Microsoft.CodeAnalysis.SemanticModel.GetOperation(Microsoft.CodeAnalysis.SyntaxNode node, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> Microsoft.CodeAnalysis.IOperation
 Microsoft.CodeAnalysis.Semantics.ArgumentKind
 Microsoft.CodeAnalysis.Semantics.ArgumentKind.DefaultValue = 3 -> Microsoft.CodeAnalysis.Semantics.ArgumentKind