Fix shadow variables reassignment for block scoping in loops. (#6814)

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

@@ -247,6 +247,8 @@ const continuationVisitor = {
         }
         state.reassignments[name] = true;
       }
+    } else if (path.isReturnStatement()) {
+      state.returnStatements.push(path);
     }
   },
 };
@@ -585,6 +587,7 @@ class BlockScoping {
   addContinuations(fn) {
     const state = {
       reassignments: {},
+      returnStatements: [],
       outsideReferences: this.outsideLetReferences,
     };
 
@@ -599,6 +602,12 @@ class BlockScoping {
 
       this.scope.rename(param.name, newParam.name, fn);
 
+      state.returnStatements.forEach(returnStatement => {
+        returnStatement.insertBefore(
+          t.expressionStatement(t.assignmentExpression("=", param, newParam)),
+        );
+      });
+
       // assign outer reference as it's been modified internally and needs to be retained
       fn.body.body.push(
         t.expressionStatement(t.assignmentExpression("=", param, newParam)),

packages/babel-plugin-transform-block-scoping/test/fixtures/exec/for-continuation-outer-reference.js

@@ -0,0 +1,13 @@
+let data = [true, false, false, true, false];
+
+for (let index = 0; index < data.length; index++) {
+    let item = data[index];
+    if (!item) {
+        data.splice(index, 1);
+        index--;
+        continue;
+    }
+    let fn = function () {item;};
+}
+
+assert(data.every(item => item));

packages/babel-plugin-transform-block-scoping/test/fixtures/general/wrap-closure-shadow-variables-reassignment/actual.js

@@ -0,0 +1,7 @@
+for (let index = 0; index < 10; index++) {
+    if (index % 2) {
+        index+=3;
+        continue;
+    }
+    let fn = function () {index;};
+}

packages/babel-plugin-transform-block-scoping/test/fixtures/general/wrap-closure-shadow-variables-reassignment/expected.js

@@ -0,0 +1,19 @@
+var _loop = function (_index) {
+  if (_index % 2) {
+    _index += 3;
+    index = _index;
+    return "continue";
+  }
+
+  var fn = function () {
+    _index;
+  };
+
+  index = _index;
+};
+
+for (var index = 0; index < 10; index++) {
+  var _ret = _loop(index);
+
+  if (_ret === "continue") continue;
+}