Move diagnostic from parser to later phase.

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

@@ -1604,7 +1604,6 @@ private TypeDeclarationSyntax ParseClassOrStructOrInterfaceDeclaration(SyntaxLis
             var typeParameters = this.ParseTypeParameterList(allowVariance: classOrStructOrInterface.Kind == SyntaxKind.InterfaceKeyword);
 
             _termState = saveTerm;
-            bool hasTypeParams = typeParameters != null;
             var baseList = this.ParseBaseList();
 
             // Parse class body
@@ -1616,7 +1615,7 @@ private TypeDeclarationSyntax ParseClassOrStructOrInterfaceDeclaration(SyntaxLis
                 if (this.CurrentToken.ContextualKind == SyntaxKind.WhereKeyword)
                 {
                     constraints = _pool.Allocate<TypeParameterConstraintClauseSyntax>();
-                    this.ParseTypeParameterConstraintClauses(hasTypeParams, constraints);
+                    this.ParseTypeParameterConstraintClauses(constraints);
                 }
 
                 var openBrace = this.EatToken(SyntaxKind.OpenBraceToken);
@@ -1916,18 +1915,11 @@ private bool IsPossibleTypeParameterConstraintClauseStart()
                 this.PeekToken(2).Kind == SyntaxKind.ColonToken;
         }
 
-        private void ParseTypeParameterConstraintClauses(bool isAllowed, SyntaxListBuilder list)
+        private void ParseTypeParameterConstraintClauses(SyntaxListBuilder list)
         {
             while (this.CurrentToken.ContextualKind == SyntaxKind.WhereKeyword)
             {
-                var constraint = this.ParseTypeParameterConstraintClause();
-                if (!isAllowed)
-                {
-                    constraint = this.AddErrorToFirstToken(constraint, ErrorCode.ERR_ConstraintOnlyAllowedOnGenericDecl);
-                    isAllowed = true; // silence any further errors
-                }
-
-                list.Add(constraint);
+                list.Add(this.ParseTypeParameterConstraintClause());
             }
         }
 
@@ -2945,7 +2937,7 @@ private bool IsEndOfNameInExplicitInterface()
                 if (this.CurrentToken.ContextualKind == SyntaxKind.WhereKeyword)
                 {
                     constraints = _pool.Allocate<TypeParameterConstraintClauseSyntax>();
-                    this.ParseTypeParameterConstraintClauses(typeParameterList != null, constraints);
+                    this.ParseTypeParameterConstraintClauses(constraints);
                 }
                 else if (this.CurrentToken.Kind == SyntaxKind.ColonToken)
                 {
@@ -5103,7 +5095,7 @@ private DelegateDeclarationSyntax ParseDelegateDeclaration(SyntaxListBuilder<Att
                 if (this.CurrentToken.ContextualKind == SyntaxKind.WhereKeyword)
                 {
                     constraints = _pool.Allocate<TypeParameterConstraintClauseSyntax>();
-                    this.ParseTypeParameterConstraintClauses(typeParameters != null, constraints);
+                    this.ParseTypeParameterConstraintClauses(constraints);
                 }
 
                 _termState = saveTerm;
@@ -8885,7 +8877,7 @@ private static bool IsAccessibilityModifier(SyntaxKind kind)
             if (this.CurrentToken.ContextualKind == SyntaxKind.WhereKeyword)
             {
                 constraints = _pool.Allocate<TypeParameterConstraintClauseSyntax>();
-                this.ParseTypeParameterConstraintClauses(typeParameterListOpt != null, constraints);
+                this.ParseTypeParameterConstraintClauses(constraints);
                 forceLocalFunc = true;
             }
 

src/Compilers/CSharp/Portable/Symbols/Source/LocalFunctionSymbol.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.Collections.Generic;
 using System.Collections.Immutable;
 using System.Diagnostics;
@@ -90,6 +91,7 @@ internal ReturnTypeAndDiagnostics(TypeSymbol returnType, ImmutableArray<Diagnost
             else
             {
                 _typeParameters = ImmutableArray<TypeParameterSymbol>.Empty;
+                ReportErrorIfHasConstraints(_syntax.ConstraintClauses, diagnostics);
             }
 
             if (IsExtensionMethod)

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

@@ -95,9 +95,14 @@ internal sealed class SourceMemberMethodSymbol : SourceMethodSymbol
 
             this.MakeFlags(methodKind, declarationModifiers, returnsVoid, isExtensionMethod, isMetadataVirtualIgnoringModifiers);
 
-            _typeParameters = (syntax.Arity == 0) ?
-                ImmutableArray<TypeParameterSymbol>.Empty :
-                MakeTypeParameters(syntax, diagnostics);
+            _typeParameters = syntax.Arity == 0
+                ? ImmutableArray<TypeParameterSymbol>.Empty
+                : MakeTypeParameters(syntax, diagnostics);
+
+            if (syntax.Arity == 0)
+            {
+                ReportErrorIfHasConstraints(syntax.ConstraintClauses, diagnostics);
+            }
 
             bool hasBlockBody = syntax.Body != null;
             _isExpressionBodied = !hasBlockBody && syntax.ExpressionBody != null;

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

@@ -118,6 +118,15 @@ private ImmutableArray<TypeParameterSymbol> MakeTypeParameters(DiagnosticBag dia
         {
             if (declaration.Arity == 0)
             {
+                if (declaration.Kind != DeclarationKind.Enum)
+                {
+                    foreach (var syntaxRef in this.SyntaxReferences)
+                    {
+                        var constraintClauses = GetConstraintClauses((CSharpSyntaxNode)syntaxRef.GetSyntax());
+                        ReportErrorIfHasConstraints(constraintClauses, diagnostics);
+                    }
+                }
+
                 return ImmutableArray<TypeParameterSymbol>.Empty;
             }
 

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

@@ -1089,6 +1089,17 @@ public ImmutableArray<SymbolDisplayPart> ToDisplayParts(SymbolDisplayFormat form
             return SymbolDisplay.ToMinimalDisplayParts(this, semanticModel, position, format);
         }
 
+        protected static void ReportErrorIfHasConstraints(
+            SyntaxList<TypeParameterConstraintClauseSyntax> constraintClauses, DiagnosticBag diagnostics)
+        {
+            if (constraintClauses.Count > 0)
+            {
+                diagnostics.Add(
+                    ErrorCode.ERR_ConstraintOnlyAllowedOnGenericDecl,
+                    constraintClauses[0].WhereKeyword.GetLocation());
+            }
+        }
+
         #region ISymbol Members
 
         SymbolKind ISymbol.Kind