Further changes to parser for OmittedExpressions, and make checker resilient to them

Author: JsonFreeman

src/compiler/checker.ts

@@ -4129,11 +4129,18 @@ module ts {
             return unknownSignature;
         }
 
-        function signatureHasCorrectArity(node: CallExpression, signature: Signature) {
+        function signatureHasCorrectArity(node: CallExpression, signature: Signature): boolean {
             var args = node.arguments || emptyArray;
-            return args.length >= signature.minArgumentCount &&
+            var isCorrect = args.length >= signature.minArgumentCount &&
                 (signature.hasRestParameter || args.length <= signature.parameters.length) &&
                 (!node.typeArguments || signature.typeParameters && node.typeArguments.length === signature.typeParameters.length);
+
+            // For error recovery, since we have parsed OmittedExpressions for any extra commas
+            // in the argument list, if we see any OmittedExpressions, just return true.
+            if (!isCorrect && forEach(node.arguments, arg => arg.kind === SyntaxKind.OmittedExpression)) {
+                return true;
+            }
+            return isCorrect;
         }
 
         // The candidate list orders groups in reverse, but within a group signatures are kept in declaration order
@@ -4208,6 +4215,9 @@ module ts {
             var mapper = createInferenceMapper(context);
             // First infer from arguments that are not context sensitive
             for (var i = 0; i < args.length; i++) {
+                if (args[i].kind === SyntaxKind.OmittedExpression) {
+                    continue;
+                }
                 if (!excludeArgument || excludeArgument[i] === undefined) {
                     var parameterType = getTypeAtPosition(signature, i);
                     inferTypes(context, checkExpressionWithContextualType(args[i], parameterType, mapper), parameterType);
@@ -4216,6 +4226,9 @@ module ts {
             // Next, infer from those context sensitive arguments that are no longer excluded
             if (excludeArgument) {
                 for (var i = 0; i < args.length; i++) {
+                    if (args[i].kind === SyntaxKind.OmittedExpression) {
+                        continue;
+                    }
                     if (excludeArgument[i] === false) {
                         var parameterType = getTypeAtPosition(signature, i);
                         inferTypes(context, checkExpressionWithContextualType(args[i], parameterType, mapper), parameterType);
@@ -4244,6 +4257,10 @@ module ts {
             if (node.arguments) {
                 for (var i = 0; i < node.arguments.length; i++) {
                     var arg = node.arguments[i];
+                    if (arg.kind === SyntaxKind.OmittedExpression) {
+                        continue;
+                    }
+
                     var paramType = getTypeAtPosition(signature, i);
                     // String literals get string literal types unless we're reporting errors
                     var argType = arg.kind === SyntaxKind.StringLiteral && !reportErrors ?

src/compiler/parser.ts

@@ -2307,7 +2307,7 @@ module ts {
                     // needs evidence of a trailing comma in order to give good results for signature help.
                     // That is why we do not allow a trailing comma, but we "preserve" a trailing comma.
                     callExpr.arguments = parseDelimitedList(ParsingContext.ArgumentExpressions,
-                        parseAssignmentExpression, /*allowTrailingComma*/ false, /*preserveTrailingComma*/ true);
+                        parseArgumentExpression, /*allowTrailingComma*/ false, /*preserveTrailingComma*/ true);
                     parseExpected(SyntaxKind.CloseParenToken);
                     expr = finishNode(callExpr);
                     continue;
@@ -2376,8 +2376,25 @@ module ts {
             return finishNode(node);
         }
 
+        function parseAssignmentExpressionOrOmittedExpression(omittedExpressionDiagnostic: DiagnosticMessage): Expression {
+            if (token === SyntaxKind.CommaToken) {
+                if (omittedExpressionDiagnostic) {
+                    var errorStart = scanner.getTokenPos();
+                    var errorLength = scanner.getTextPos() - errorStart;
+                    grammarErrorAtPos(errorStart, errorLength, omittedExpressionDiagnostic);
+                }
+                return createNode(SyntaxKind.OmittedExpression);
+            }
+            
+            return parseAssignmentExpression();
+        }
+
         function parseArrayLiteralElement(): Expression {
-            return token === SyntaxKind.CommaToken ? createNode(SyntaxKind.OmittedExpression) : parseAssignmentExpression();
+            return parseAssignmentExpressionOrOmittedExpression(/*omittedExpressionDiagnostic*/ undefined);
+        }
+
+        function parseArgumentExpression(): Expression {
+            return parseAssignmentExpressionOrOmittedExpression(Diagnostics.Argument_expression_expected);
         }
 
         function parseArrayLiteral(): ArrayLiteral {
@@ -2523,7 +2540,7 @@ module ts {
                 // needs evidence of a trailing comma in order to give good results for signature help.
                 // That is why we do not allow a trailing comma, but we "preserve" a trailing comma.
                 node.arguments = parseDelimitedList(ParsingContext.ArgumentExpressions,
-                    parseAssignmentExpression, /*allowTrailingComma*/ false, /*preserveTrailingComma*/ true);
+                    parseArgumentExpression, /*allowTrailingComma*/ false, /*preserveTrailingComma*/ true);
                 parseExpected(SyntaxKind.CloseParenToken);
             }
             return finishNode(node);