rename colliding let bindings with for loop init (#8937)

* rename colliding let bindings with for loop init

* added complex test case to check if loop init collisions were handled correctly

* updated test files

packages/babel-plugin-transform-block-scoping/src/index.js

@@ -460,7 +460,9 @@ class BlockScoping {
 
   remap() {
     const letRefs = this.letReferences;
+    const outsideLetRefs = this.outsideLetReferences;
     const scope = this.scope;
+    const blockPathScope = this.blockPath.scope;
 
     // alright, so since we aren't wrapping this block in a closure
     // we have to check if any of our let variables collide with
@@ -481,11 +483,20 @@ class BlockScoping {
           scope.rename(ref.name);
         }
 
-        if (this.blockPath.scope.hasOwnBinding(key)) {
-          this.blockPath.scope.rename(ref.name);
+        if (blockPathScope.hasOwnBinding(key)) {
+          blockPathScope.rename(ref.name);
         }
       }
     }
+
+    for (const key in outsideLetRefs) {
+      const ref = letRefs[key];
+      // check for collisions with a for loop's init variable and the enclosing scope's bindings
+      // https://github.com/babel/babel/issues/8498
+      if (isInLoop(this.blockPath) && blockPathScope.hasOwnBinding(key)) {
+        blockPathScope.rename(ref.name);
+      }
+    }
   }
 
   wrapClosure() {

packages/babel-plugin-transform-block-scoping/test/fixtures/general/issue-8498-loop-init-collision-destructuring/input.js

@@ -0,0 +1,7 @@
+for (let a, { b } = {};;) {
+  let a, { b } = {};
+
+  {
+    let a, { b } = {};
+  }
+}

packages/babel-plugin-transform-block-scoping/test/fixtures/general/issue-8498-loop-init-collision-destructuring/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["transform-destructuring", "transform-block-scoping"]
+}

packages/babel-plugin-transform-block-scoping/test/fixtures/general/issue-8498-loop-init-collision-destructuring/output.js

@@ -0,0 +1,11 @@
+for (var a, _ref = {}, b = _ref.b;;) {
+  var _a = void 0,
+      _ref2 = {},
+      _b = _ref2.b;
+
+  {
+    var _a2 = void 0,
+        _ref3 = {},
+        _b2 = _ref3.b;
+  }
+}

packages/babel-plugin-transform-block-scoping/test/fixtures/general/issue-8498-loop-init-collision/input.js

@@ -0,0 +1,8 @@
+for (let i = 0; i < 3; i++) {
+    let i = 'abc';
+    console.log(i);
+
+    {
+      let i = "hello";
+    }
+}

packages/babel-plugin-transform-block-scoping/test/fixtures/general/issue-8498-loop-init-collision/output.js

@@ -0,0 +1,7 @@
+for (var i = 0; i < 3; i++) {
+  var _i = 'abc';
+  console.log(_i);
+  {
+    var _i2 = "hello";
+  }
+}