Support Trailing Commas

src/compiler/checker.ts

@@ -17244,7 +17244,8 @@ namespace ts {
         }
 
         function checkGrammarForDisallowedTrailingComma(list: NodeArray<Node>): boolean {
-            if (list && list.hasTrailingComma) {
+            if (list && list.hasTrailingComma &&
+                !(list[0].parent.kind === SyntaxKind.FunctionDeclaration || list[0].parent.kind === SyntaxKind.ArrowFunction)) {
                 const start = list.end - ",".length;
                 const end = list.end;
                 const sourceFile = getSourceFileOfNode(list[0]);

tests/baselines/reference/ArrowFunction2.errors.txt

@@ -1,12 +1,9 @@
 tests/cases/conformance/parser/ecmascript5/ErrorRecovery/ArrowFunctions/ArrowFunction2.ts(1,13): error TS2304: Cannot find name 'b'.
-tests/cases/conformance/parser/ecmascript5/ErrorRecovery/ArrowFunctions/ArrowFunction2.ts(1,14): error TS1009: Trailing comma not allowed.
 
 
-==== tests/cases/conformance/parser/ecmascript5/ErrorRecovery/ArrowFunctions/ArrowFunction2.ts (2 errors) ====
+==== tests/cases/conformance/parser/ecmascript5/ErrorRecovery/ArrowFunctions/ArrowFunction2.ts (1 errors) ====
     var v = (a: b,) => {
                 ~
 !!! error TS2304: Cannot find name 'b'.
-                 ~
-!!! error TS1009: Trailing comma not allowed.
 
     };

tests/baselines/reference/parserParameterList12.symbols

@@ -0,0 +1,5 @@
+=== tests/cases/conformance/parser/ecmascript5/ParameterLists/parserParameterList12.ts ===
+function F(a,) {
+>F : Symbol(F, Decl(parserParameterList12.ts, 0, 0))
+>a : Symbol(a, Decl(parserParameterList12.ts, 0, 11))
+}

tests/baselines/reference/parserParameterList12.types

@@ -0,0 +1,5 @@
+=== tests/cases/conformance/parser/ecmascript5/ParameterLists/parserParameterList12.ts ===
+function F(a,) {
+>F : (a: any) => void
+>a : any
+}

tests/baselines/reference/parserX_ArrowFunction2.errors.txt

@@ -1,12 +1,9 @@
 tests/cases/conformance/parser/ecmascript5/ErrorRecovery/ArrowFunctions/parserX_ArrowFunction2.ts(1,13): error TS2304: Cannot find name 'b'.
-tests/cases/conformance/parser/ecmascript5/ErrorRecovery/ArrowFunctions/parserX_ArrowFunction2.ts(1,14): error TS1009: Trailing comma not allowed.
 
 
-==== tests/cases/conformance/parser/ecmascript5/ErrorRecovery/ArrowFunctions/parserX_ArrowFunction2.ts (2 errors) ====
+==== tests/cases/conformance/parser/ecmascript5/ErrorRecovery/ArrowFunctions/parserX_ArrowFunction2.ts (1 errors) ====
     var v = (a: b,) => {
                 ~
 !!! error TS2304: Cannot find name 'b'.
-                 ~
-!!! error TS1009: Trailing comma not allowed.
 
     };

tests/baselines/reference/trailingCommasInFunctionParameter.js

@@ -0,0 +1,14 @@
+//// [trailingCommasInFunctionParameter.ts]
+function f1(x, y,) {
+}
+
+function f2() {
+    return (x,) => {}
+}
+
+//// [trailingCommasInFunctionParameter.js]
+function f1(x, y) {
+}
+function f2() {
+    return function (x) { };
+}

tests/baselines/reference/trailingCommasInFunctionParameter.symbols

@@ -0,0 +1,13 @@
+=== tests/cases/conformance/es7/trailingCommasInFunctionParamLists/trailingCommasInFunctionParameter.ts ===
+function f1(x, y,) {
+>f1 : Symbol(f1, Decl(trailingCommasInFunctionParameter.ts, 0, 0))
+>x : Symbol(x, Decl(trailingCommasInFunctionParameter.ts, 0, 12))
+>y : Symbol(y, Decl(trailingCommasInFunctionParameter.ts, 0, 14))
+}
+
+function f2() {
+>f2 : Symbol(f2, Decl(trailingCommasInFunctionParameter.ts, 1, 1))
+
+    return (x,) => {}
+>x : Symbol(x, Decl(trailingCommasInFunctionParameter.ts, 4, 12))
+}

tests/baselines/reference/trailingCommasInFunctionParameter.types

@@ -0,0 +1,14 @@
+=== tests/cases/conformance/es7/trailingCommasInFunctionParamLists/trailingCommasInFunctionParameter.ts ===
+function f1(x, y,) {
+>f1 : (x: any, y: any) => void
+>x : any
+>y : any
+}
+
+function f2() {
+>f2 : () => (x: any) => void
+
+    return (x,) => {}
+>(x,) => {} : (x: any) => void
+>x : any
+}

tests/cases/conformance/es7/trailingCommasInFunctionParamLists/trailingCommasInFunctionParameter.ts

@@ -0,0 +1,7 @@
+// @target: es5
+function f1(x, y,) {
+}
+
+function f2() {
+    return (x,) => {}
+}