Remove TrailingCommaBehavior in favor of two boolean parameters

Author: JsonFreeman

src/compiler/parser.ts

@@ -626,12 +626,6 @@ module ts {
         Parameters,              // Parameters in parameter list
     }
 
-    enum TrailingCommaBehavior {
-        Disallow,
-        Allow,
-        Preserve
-    }
-
     // Tracks whether we nested (directly or indirectly) in a certain control block.
     // Used for validating break and continue statements.
     enum ControlBlockContext {
@@ -1203,7 +1197,7 @@ module ts {
         }
 
         // Parses a comma-delimited list of elements
-        function parseDelimitedList<T extends Node>(kind: ParsingContext, parseElement: () => T, trailingCommaBehavior: TrailingCommaBehavior): NodeArray<T> {
+        function parseDelimitedList<T extends Node>(kind: ParsingContext, parseElement: () => T, allowTrailingComma: boolean, preserveTrailingComma: boolean): NodeArray<T> {
             var saveParsingContext = parsingContext;
             parsingContext |= 1 << kind;
             var result = <NodeArray<T>>[];
@@ -1228,13 +1222,13 @@ module ts {
                 else if (isListTerminator(kind)) {
                     // Check if the last token was a comma.
                     if (commaStart >= 0) {
-                        if (trailingCommaBehavior === TrailingCommaBehavior.Disallow) {
+                        if (!allowTrailingComma) {
                             if (file.syntacticErrors.length === errorCountBeforeParsingList) {
                                 // Report a grammar error so we don't affect lookahead
                                 grammarErrorAtPos(commaStart, scanner.getStartPos() - commaStart, Diagnostics.Trailing_comma_not_allowed);
                             }
                         }
-                        else if (trailingCommaBehavior === TrailingCommaBehavior.Preserve) {
+                        else if (preserveTrailingComma) {
                             result.push(<T>createNode(SyntaxKind.OmittedExpression));
                         }
                     }
@@ -1271,7 +1265,7 @@ module ts {
 
         function parseBracketedList<T extends Node>(kind: ParsingContext, parseElement: () => T, startToken: SyntaxKind, endToken: SyntaxKind): NodeArray<T> {
             if (parseExpected(startToken)) {
-                var result = parseDelimitedList(kind, parseElement, TrailingCommaBehavior.Disallow);
+                var result = parseDelimitedList(kind, parseElement, /*allowTrailingComma*/ false, /*preserveTrailingComma*/ false);
                 parseExpected(endToken);
                 return result;
             }
@@ -2307,7 +2301,8 @@ module ts {
                     else {
                         parseExpected(SyntaxKind.OpenParenToken);
                     }
-                    callExpr.arguments = parseDelimitedList(ParsingContext.ArgumentExpressions, parseAssignmentExpression, TrailingCommaBehavior.Disallow);
+                    callExpr.arguments = parseDelimitedList(ParsingContext.ArgumentExpressions,
+                        parseAssignmentExpression, /*allowTrailingComma*/ false, /*preserveTrailingComma*/ false);
                     parseExpected(SyntaxKind.CloseParenToken);
                     expr = finishNode(callExpr);
                     continue;
@@ -2384,7 +2379,8 @@ module ts {
             var node = <ArrayLiteral>createNode(SyntaxKind.ArrayLiteral);
             parseExpected(SyntaxKind.OpenBracketToken);
             if (scanner.hasPrecedingLineBreak()) node.flags |= NodeFlags.MultiLine;
-            node.elements = parseDelimitedList(ParsingContext.ArrayLiteralMembers, parseArrayLiteralElement, TrailingCommaBehavior.Preserve);
+            node.elements = parseDelimitedList(ParsingContext.ArrayLiteralMembers, 
+                parseArrayLiteralElement, /*allowTrailingComma*/ true, /*preserveTrailingComma*/ true);
             parseExpected(SyntaxKind.CloseBracketToken);
             return finishNode(node);
         }
@@ -2427,9 +2423,9 @@ module ts {
             }
 
             // ES3 itself does not accept a trailing comma in an object literal, however, we'd like to preserve it in ES5.
-            var trailingCommaBehavior = languageVersion === ScriptTarget.ES3 ? TrailingCommaBehavior.Allow : TrailingCommaBehavior.Preserve;
+            var preserveTrailingComma = languageVersion !== ScriptTarget.ES3;
 
-            node.properties = parseDelimitedList(ParsingContext.ObjectLiteralMembers, parseObjectLiteralMember, trailingCommaBehavior);
+            node.properties = parseDelimitedList(ParsingContext.ObjectLiteralMembers, parseObjectLiteralMember, /*allowTrailingComma*/ true, preserveTrailingComma);
             parseExpected(SyntaxKind.CloseBraceToken);
 
             var seen: Map<SymbolFlags> = {};
@@ -2518,7 +2514,8 @@ module ts {
             parseExpected(SyntaxKind.NewKeyword);
             node.func = parseCallAndAccess(parsePrimaryExpression(), /* inNewExpression */ true);
             if (parseOptional(SyntaxKind.OpenParenToken) || token === SyntaxKind.LessThanToken && (node.typeArguments = tryParse(parseTypeArgumentsAndOpenParen))) {
-                node.arguments = parseDelimitedList(ParsingContext.ArgumentExpressions, parseAssignmentExpression, TrailingCommaBehavior.Disallow);
+                node.arguments = parseDelimitedList(ParsingContext.ArgumentExpressions,
+                    parseAssignmentExpression, /*allowTrailingComma*/ false, /*preserveTrailingComma*/ false);
                 parseExpected(SyntaxKind.CloseParenToken);
             }
             return finishNode(node);
@@ -3087,7 +3084,8 @@ module ts {
         }
 
         function parseVariableDeclarationList(flags: NodeFlags, noIn?: boolean): NodeArray<VariableDeclaration> {
-            return parseDelimitedList(ParsingContext.VariableDeclarations, () => parseVariableDeclaration(flags, noIn), TrailingCommaBehavior.Disallow);
+            return parseDelimitedList(ParsingContext.VariableDeclarations,
+                () => parseVariableDeclaration(flags, noIn), /*allowTrailingComma*/ false, /*preserveTrailingComma*/ false);
         }
 
         function parseVariableStatement(pos?: number, flags?: NodeFlags): VariableStatement {
@@ -3486,7 +3484,8 @@ module ts {
             var implementsKeywordLength: number;
             if (parseOptional(SyntaxKind.ImplementsKeyword)) {
                 implementsKeywordLength = scanner.getStartPos() - implementsKeywordStart;
-                node.implementedTypes = parseDelimitedList(ParsingContext.BaseTypeReferences, parseTypeReference, TrailingCommaBehavior.Disallow);
+                node.implementedTypes = parseDelimitedList(ParsingContext.BaseTypeReferences,
+                    parseTypeReference, /*allowTrailingComma*/ false, /*preserveTrailingComma*/ false);
             }
             var errorCountBeforeClassBody = file.syntacticErrors.length;
             if (parseExpected(SyntaxKind.OpenBraceToken)) {
@@ -3514,7 +3513,8 @@ module ts {
             var extendsKeywordLength: number;
             if (parseOptional(SyntaxKind.ExtendsKeyword)) {
                 extendsKeywordLength = scanner.getStartPos() - extendsKeywordStart;
-                node.baseTypes = parseDelimitedList(ParsingContext.BaseTypeReferences, parseTypeReference, TrailingCommaBehavior.Disallow);
+                node.baseTypes = parseDelimitedList(ParsingContext.BaseTypeReferences,
+                    parseTypeReference, /*allowTrailingComma*/ false, /*preserveTrailingComma*/ false);
             }
             var errorCountBeforeInterfaceBody = file.syntacticErrors.length;
             node.members = parseTypeLiteral().members;
@@ -3578,7 +3578,8 @@ module ts {
             parseExpected(SyntaxKind.EnumKeyword);
             node.name = parseIdentifier();
             if (parseExpected(SyntaxKind.OpenBraceToken)) {
-                node.members = parseDelimitedList(ParsingContext.EnumMembers, parseAndCheckEnumMember, TrailingCommaBehavior.Allow);
+                node.members = parseDelimitedList(ParsingContext.EnumMembers,
+                    parseAndCheckEnumMember, /*allowTrailingComma*/ true, /*preserveTrailingComma*/ false);
                 parseExpected(SyntaxKind.CloseBraceToken);
             }
             else {