Disallow duplicate params in methods (#9599)

* Disallow duplicate params in methods

* Fix plugins

packages/babel-parser/src/parser/expression.js

@@ -1740,7 +1740,7 @@ export default class ExpressionParser extends LValParser {
     );
     this.parseFunctionParams((node: any), allowModifiers);
     this.checkYieldAwaitInDefaultParams();
-    this.parseFunctionBodyAndFinish(node, type);
+    this.parseFunctionBodyAndFinish(node, type, true);
 
     this.state.yieldPos = oldYieldPos;
     this.state.awaitPos = oldAwaitPos;
@@ -1804,14 +1804,19 @@ export default class ExpressionParser extends LValParser {
   parseFunctionBodyAndFinish(
     node: N.BodilessFunctionOrMethodBase,
     type: string,
+    isMethod?: boolean = false,
   ): void {
     // $FlowIgnore (node is not bodiless if we get here)
-    this.parseFunctionBody(node);
+    this.parseFunctionBody(node, false, isMethod);
     this.finishNode(node, type);
   }
 
   // Parse function body and check parameters.
-  parseFunctionBody(node: N.Function, allowExpression: ?boolean): void {
+  parseFunctionBody(
+    node: N.Function,
+    allowExpression: ?boolean,
+    isMethod?: boolean = false,
+  ): void {
     const isExpression = allowExpression && !this.match(tt.braceL);
     const oldStrict = this.state.strict;
     let useStrict = false;
@@ -1853,7 +1858,7 @@ export default class ExpressionParser extends LValParser {
       // if a let/const declaration in the function clashes with one of the params.
       this.checkParams(
         node,
-        !oldStrict && !useStrict && !allowExpression && !nonSimple,
+        !oldStrict && !useStrict && !allowExpression && !isMethod && !nonSimple,
         allowExpression,
       );
       node.body = this.parseBlock(true, false);

packages/babel-parser/src/plugins/estree.js

@@ -259,8 +259,12 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       return node;
     }
 
-    parseFunctionBody(node: N.Function, allowExpression: ?boolean): void {
-      super.parseFunctionBody(node, allowExpression);
+    parseFunctionBody(
+      node: N.Function,
+      allowExpression: ?boolean,
+      isMethod?: boolean = false,
+    ): void {
+      super.parseFunctionBody(node, allowExpression, isMethod);
       node.expression = node.body.type !== "BlockStatement";
     }
 

packages/babel-parser/src/plugins/flow.js

@@ -1544,19 +1544,24 @@ export default (superClass: Class<Parser>): Class<Parser> =>
     // Overrides
     // ==================================
 
-    parseFunctionBody(node: N.Function, allowExpressionBody: ?boolean): void {
+    parseFunctionBody(
+      node: N.Function,
+      allowExpressionBody: ?boolean,
+      isMethod?: boolean = false,
+    ): void {
       if (allowExpressionBody) {
         return this.forwardNoArrowParamsConversionAt(node, () =>
-          super.parseFunctionBody(node, true),
+          super.parseFunctionBody(node, true, isMethod),
         );
       }
 
-      return super.parseFunctionBody(node, false);
+      return super.parseFunctionBody(node, false, isMethod);
     }
 
     parseFunctionBodyAndFinish(
       node: N.BodilessFunctionOrMethodBase,
       type: string,
+      isMethod?: boolean = false,
     ): void {
       if (this.match(tt.colon)) {
         const typeNode = this.startNode();
@@ -1573,7 +1578,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
           : null;
       }
 
-      super.parseFunctionBodyAndFinish(node, type);
+      super.parseFunctionBodyAndFinish(node, type, isMethod);
     }
 
     // interfaces

packages/babel-parser/src/plugins/typescript.js

@@ -1472,6 +1472,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
     parseFunctionBodyAndFinish(
       node: N.BodilessFunctionOrMethodBase,
       type: string,
+      isMethod?: boolean = false,
     ): void {
       if (this.match(tt.colon)) {
         node.returnType = this.tsParseTypeOrTypePredicateAnnotation(tt.colon);
@@ -1488,7 +1489,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
         return;
       }
 
-      super.parseFunctionBodyAndFinish(node, type);
+      super.parseFunctionBodyAndFinish(node, type, isMethod);
     }
 
     parseSubscript(

packages/babel-parser/test/fixtures/es2015/class-methods/disallow-duplicate-method-params/input.js

@@ -0,0 +1,3 @@
+class Foo {
+    bar(a, a) {}
+}

packages/babel-parser/test/fixtures/es2015/class-methods/disallow-duplicate-method-params/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "Argument name clash (2:11)"
+}

packages/babel-parser/test/fixtures/es2015/object/disallow-duplicate-method-params/input.js

@@ -0,0 +1,3 @@
+({
+    bar(a, a) {}
+})

packages/babel-parser/test/fixtures/es2015/object/disallow-duplicate-method-params/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "Argument name clash (2:11)"
+}