Fix arrow functions in derived class constructors

Fixes #1987

Author: arv

src/codegeneration/ParenTrait.js

@@ -15,6 +15,7 @@
 import {
   ArgumentList,
   ArrayLiteral,
+  BinaryExpression,
   ExpressionStatement,
   NewExpression,
   ParenExpression,
@@ -141,5 +142,20 @@ export function ParenTrait(ParseTreeTransformerClass) {
       }
       return new PropertyNameAssignment(tree.location, name, value);
     }
+
+    transformBinaryExpression(tree) {
+      let left = this.transformAny(tree.left);
+      let right = this.transformAny(tree.right);
+      if (left.type === COMMA_EXPRESSION) {
+        left = wrap(left);
+      }
+      if (right.type === COMMA_EXPRESSION) {
+        right = wrap(right);
+      }
+      if (left === tree.left && right === tree.right) {
+        return tree;
+      }
+      return new BinaryExpression(tree.location, left, tree.operator, right);
+    }
   };
 }

test/feature/ArrowFunctions/InDerivedClassConstructor.js

@@ -0,0 +1,20 @@
+class Base {
+  bar() {
+    return 1;
+  }
+}
+
+class Derived extends Base {
+  constructor() {
+    super()
+    this.foo = () => {
+      return this.bar();
+    };
+  }
+  bar() {
+    return 2;
+  }
+}
+
+let d = new Derived();
+assert.equal(2, (0, d).foo());