From d2a0a89ad73ca7ee97559b3ac70fb826eb83d99e Mon Sep 17 00:00:00 2001
From: CyrusNajmabadi <cyrusn@microsoft.com>
Date: Wed, 17 May 2017 13:46:51 -0700
Subject: [PATCH] 	Simplify implementation of parsing constraints.

---
 .../CSharp/Portable/Parser/LanguageParser.cs  | 77 ++++++++-----------
 1 file changed, 31 insertions(+), 46 deletions(-)

diff --git a/src/Compilers/CSharp/Portable/Parser/LanguageParser.cs b/src/Compilers/CSharp/Portable/Parser/LanguageParser.cs
index c3f845c305e72..011199d64b135 100644
--- a/src/Compilers/CSharp/Portable/Parser/LanguageParser.cs
+++ b/src/Compilers/CSharp/Portable/Parser/LanguageParser.cs
@@ -1859,8 +1859,8 @@ private bool IsPossibleMemberStartOrStop()
         private bool IsPossibleAggregateClauseStartOrStop()
         {
             return this.CurrentToken.Kind == SyntaxKind.ColonToken
-                || this.IsPossibleTypeParameterConstraintClauseStart()
-                || this.CurrentToken.Kind == SyntaxKind.OpenBraceToken;
+                || this.CurrentToken.Kind == SyntaxKind.OpenBraceToken
+                || this.IsCurrentTokenWhereOfConstraintClause();
         }
 
         private BaseListSyntax ParseBaseList()
@@ -1875,42 +1875,26 @@ private BaseListSyntax ParseBaseList()
             try
             {
                 // first type
-                if (this.IsPossibleTypeParameterConstraintClauseStart())
-                {
-                    list.Add(_syntaxFactory.SimpleBaseType(this.AddError(this.CreateMissingIdentifierName(), ErrorCode.ERR_TypeExpected)));
-                }
-                else
-                {
-                    TypeSyntax firstType = this.ParseType();
-
-                    list.Add(_syntaxFactory.SimpleBaseType(firstType));
+                TypeSyntax firstType = this.ParseType();
+                list.Add(_syntaxFactory.SimpleBaseType(firstType));
 
-                    // any additional types
-                    while (true)
+                // any additional types
+                while (true)
+                {
+                    if (this.CurrentToken.Kind == SyntaxKind.OpenBraceToken ||
+                        this.IsCurrentTokenWhereOfConstraintClause())
                     {
-                        if (this.CurrentToken.Kind == SyntaxKind.OpenBraceToken
-                            || this.IsPossibleTypeParameterConstraintClauseStart())
-                        {
-                            break;
-                        }
-                        else if (this.CurrentToken.Kind == SyntaxKind.CommaToken || this.IsPossibleType())
-                        {
-                            list.AddSeparator(this.EatToken(SyntaxKind.CommaToken));
-                            if (this.IsPossibleTypeParameterConstraintClauseStart())
-                            {
-                                list.Add(_syntaxFactory.SimpleBaseType(this.AddError(this.CreateMissingIdentifierName(), ErrorCode.ERR_TypeExpected)));
-                            }
-                            else
-                            {
-                                list.Add(_syntaxFactory.SimpleBaseType(this.ParseType()));
-                            }
-
-                            continue;
-                        }
-                        else if (this.SkipBadBaseListTokens(ref colon, list, SyntaxKind.CommaToken) == PostSkipAction.Abort)
-                        {
-                            break;
-                        }
+                        break;
+                    }
+                    else if (this.CurrentToken.Kind == SyntaxKind.CommaToken || this.IsPossibleType())
+                    {
+                        list.AddSeparator(this.EatToken(SyntaxKind.CommaToken));
+                        list.Add(_syntaxFactory.SimpleBaseType(this.ParseType()));
+                        continue;
+                    }
+                    else if (this.SkipBadBaseListTokens(ref colon, list, SyntaxKind.CommaToken) == PostSkipAction.Abort)
+                    {
+                        break;
                     }
                 }
 
@@ -1926,11 +1910,11 @@ private PostSkipAction SkipBadBaseListTokens(ref SyntaxToken colon, SeparatedSyn
         {
             return this.SkipBadSeparatedListTokensWithExpectedKind(ref colon, list,
                 p => p.CurrentToken.Kind != SyntaxKind.CommaToken && !p.IsPossibleAttribute(),
-                p => p.CurrentToken.Kind == SyntaxKind.OpenBraceToken || p.IsPossibleTypeParameterConstraintClauseStart() || p.IsTerminator(),
+                p => p.CurrentToken.Kind == SyntaxKind.OpenBraceToken || p.IsCurrentTokenWhereOfConstraintClause() || p.IsTerminator(),
                 expected);
         }
 
-        private bool IsPossibleTypeParameterConstraintClauseStart()
+        private bool IsCurrentTokenWhereOfConstraintClause()
         {
             return
                 this.CurrentToken.ContextualKind == SyntaxKind.WhereKeyword &&
@@ -1949,7 +1933,7 @@ private void ParseTypeParameterConstraintClauses(SyntaxListBuilder list)
         private TypeParameterConstraintClauseSyntax ParseTypeParameterConstraintClause()
         {
             var where = this.EatContextualToken(SyntaxKind.WhereKeyword);
-            var name = (this.IsPossibleTypeParameterConstraintClauseStart() || !IsTrueIdentifier())
+            var name = !IsTrueIdentifier()
                 ? this.AddError(this.CreateMissingIdentifierName(), ErrorCode.ERR_IdentifierExpected)
                 : this.ParseIdentifierName();
 
@@ -1959,7 +1943,7 @@ private TypeParameterConstraintClauseSyntax ParseTypeParameterConstraintClause()
             try
             {
                 // first bound
-                if (this.CurrentToken.Kind == SyntaxKind.OpenBraceToken || this.IsPossibleTypeParameterConstraintClauseStart())
+                if (this.CurrentToken.Kind == SyntaxKind.OpenBraceToken || this.IsCurrentTokenWhereOfConstraintClause())
                 {
                     bounds.Add(_syntaxFactory.TypeConstraint(this.AddError(this.CreateMissingIdentifierName(), ErrorCode.ERR_TypeExpected)));
                 }
@@ -1979,7 +1963,7 @@ private TypeParameterConstraintClauseSyntax ParseTypeParameterConstraintClause()
                         else if (this.CurrentToken.Kind == SyntaxKind.CommaToken || this.IsPossibleTypeParameterConstraint())
                         {
                             bounds.AddSeparator(this.EatToken(SyntaxKind.CommaToken));
-                            if (this.IsPossibleTypeParameterConstraintClauseStart())
+                            if (this.IsCurrentTokenWhereOfConstraintClause())
                             {
                                 bounds.Add(_syntaxFactory.TypeConstraint(this.AddError(this.CreateMissingIdentifierName(), ErrorCode.ERR_TypeExpected)));
                                 break;
@@ -2047,7 +2031,7 @@ private PostSkipAction SkipBadTypeParameterConstraintTokens(SeparatedSyntaxListB
             Debug.Assert(list.Count > 0);
             return this.SkipBadSeparatedListTokensWithExpectedKind(ref tmp, list,
                 p => this.CurrentToken.Kind != SyntaxKind.CommaToken && !this.IsPossibleTypeParameterConstraint(),
-                p => this.CurrentToken.Kind == SyntaxKind.OpenBraceToken || this.IsPossibleTypeParameterConstraintClauseStart() || this.IsTerminator(),
+                p => this.CurrentToken.Kind == SyntaxKind.OpenBraceToken || this.IsCurrentTokenWhereOfConstraintClause() || this.IsTerminator(),
                 expected);
         }
 
@@ -2835,7 +2819,7 @@ private bool IsEndOfTypeParameterList()
                 return true;
             }
 
-            if (IsPossibleTypeParameterConstraintClauseStart())
+            if (IsCurrentTokenWhereOfConstraintClause())
             {
                 // class C<T where T :
                 return true;
@@ -5041,7 +5025,8 @@ private bool IsTrueIdentifier()
             if (this.CurrentToken.Kind == SyntaxKind.IdentifierToken)
             {
                 if (!IsCurrentTokenPartialKeywordOfPartialMethodOrType() &&
-                    !IsCurrentTokenQueryKeywordInQuery())
+                    !IsCurrentTokenQueryKeywordInQuery() &&
+                    !IsCurrentTokenWhereOfConstraintClause())
                 {
                     return true;
                 }
@@ -5149,7 +5134,7 @@ private TypeParameterListSyntax ParseTypeParameterList()
                 // remaining parameter & commas
                 while (true)
                 {
-                    if (this.CurrentToken.Kind == SyntaxKind.GreaterThanToken || this.IsPossibleTypeParameterConstraintClauseStart())
+                    if (this.CurrentToken.Kind == SyntaxKind.GreaterThanToken || this.IsCurrentTokenWhereOfConstraintClause())
                     {
                         break;
                     }
@@ -5186,7 +5171,7 @@ private PostSkipAction SkipBadTypeParameterListTokens(SeparatedSyntaxListBuilder
 
         private TypeParameterSyntax ParseTypeParameter()
         {
-            if (this.IsPossibleTypeParameterConstraintClauseStart())
+            if (this.IsCurrentTokenWhereOfConstraintClause())
             {
                 return _syntaxFactory.TypeParameter(
                     default(SyntaxList<AttributeListSyntax>),