Merge pull request #693 from babel/trailing-comma-rest-param

Raise error if trailing comma after rest element in async func params

scripts/test262_whitelist.txt

@@ -123,8 +123,6 @@ language/expressions/async-arrow-function/early-errors-arrow-formals-body-duplic
 language/expressions/async-arrow-function/early-errors-arrow-formals-body-duplicate.js(strict mode)
 language/expressions/async-arrow-function/escaped-async.js(default)
 language/expressions/async-arrow-function/escaped-async.js(strict mode)
-language/expressions/async-arrow-function/rest-params-trailing-comma-early-error.js(default)
-language/expressions/async-arrow-function/rest-params-trailing-comma-early-error.js(strict mode)
 language/expressions/async-function/early-errors-expression-formals-body-duplicate.js(default)
 language/expressions/async-function/early-errors-expression-formals-body-duplicate.js(strict mode)
 language/expressions/async-function/escaped-async.js(default)

src/parser/expression.js

@@ -494,14 +494,29 @@ export default class ExpressionParser extends LValParser {
 
       const node = this.startNodeAt(startPos, startLoc);
       node.callee = base;
+
+      // TODO: Clean up/merge this into `this.state` or a class like acorn's
+      // `DestructuringErrors` alongside refShorthandDefaultPos and
+      // refNeedsArrowPos.
+      const refTrailingCommaPos: Pos = { start: -1 };
+
       node.arguments = this.parseCallExpressionArguments(
         tt.parenR,
         possibleAsync,
+        refTrailingCommaPos,
       );
       this.finishCallExpression(node);
 
       if (possibleAsync && this.shouldParseAsyncArrow()) {
         state.stop = true;
+
+        if (refTrailingCommaPos.start > -1) {
+          this.raise(
+            refTrailingCommaPos.start,
+            "A trailing comma is not permitted after the rest element",
+          );
+        }
+
         return this.parseAsyncArrowFromCallExpression(
           this.startNodeAt(startPos, startLoc),
           node,
@@ -547,6 +562,7 @@ export default class ExpressionParser extends LValParser {
   parseCallExpressionArguments(
     close: TokenType,
     possibleAsyncArrow: boolean,
+    refTrailingCommaPos?: Pos,
   ): $ReadOnlyArray<?N.Expression> {
     const elts = [];
     let innerParenStart;
@@ -570,6 +586,7 @@ export default class ExpressionParser extends LValParser {
           false,
           possibleAsyncArrow ? { start: 0 } : undefined,
           possibleAsyncArrow ? { start: 0 } : undefined,
+          possibleAsyncArrow ? refTrailingCommaPos : undefined,
         ),
       );
     }
@@ -911,6 +928,14 @@ export default class ExpressionParser extends LValParser {
             spreadNodeStartLoc,
           ),
         );
+
+        if (this.match(tt.comma) && this.lookahead().type === tt.parenR) {
+          this.raise(
+            this.state.start,
+            "A trailing comma is not permitted after the rest element",
+          );
+        }
+
         break;
       } else {
         exprList.push(
@@ -1539,12 +1564,17 @@ export default class ExpressionParser extends LValParser {
     allowEmpty: ?boolean,
     refShorthandDefaultPos: ?Pos,
     refNeedsArrowPos: ?Pos,
+    refTrailingCommaPos?: Pos,
   ): ?N.Expression {
     let elt;
     if (allowEmpty && this.match(tt.comma)) {
       elt = null;
     } else if (this.match(tt.ellipsis)) {
       elt = this.parseSpread(refShorthandDefaultPos);
+
+      if (refTrailingCommaPos && this.match(tt.comma)) {
+        refTrailingCommaPos.start = this.state.start;
+      }
     } else {
       elt = this.parseMaybeAssign(
         false,

test/fixtures/es2015/arrow-functions/params-invalid-rest-trailing-comma/actual.js

@@ -0,0 +1 @@
+(...a,) => {};

test/fixtures/es2015/arrow-functions/params-invalid-rest-trailing-comma/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "A trailing comma is not permitted after the rest element (1:5)"
+}

test/fixtures/es2017/async-functions/params-invalid-rest-trailing-comma/actual.js

@@ -0,0 +1 @@
+async (...a,) => {};

test/fixtures/es2017/async-functions/params-invalid-rest-trailing-comma/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "A trailing comma is not permitted after the rest element (1:11)"
+}