Fix export bindings not updated by 'for...in' and 'for...of' (babel#1…

…1074)

* Correctly transpile export bindings for some for-of loops

* Correctly transform non-destructured for of loops to update exported variables

* Add tests

* Don't replace entire for of loop

* Correctly transform destructured for-of/for-in exports

* Update exported variables in array pattern and more fixes

* Refresh test output

* Update tests and rebase on master

* Refactor ForOf|ForIn visitor

* Don't transform re-declared exported vars

* Generate better name for loop id

Co-Authored-By: Nicolò Ribaudo <nicolo.ribaudo@gmail.com>

* Idiomatically generate UidIdentifier

* Update scope after replacing loop declaration

Co-authored-by: Nicolò Ribaudo <nicolo.ribaudo@gmail.com>

packages/babel-helper-module-transforms/src/rewrite-live-references.js

@@ -306,4 +306,40 @@ const rewriteReferencesVisitor = {
       }
     },
   },
+  "ForOfStatement|ForInStatement"(path) {
+    const { scope, node } = path;
+    const { left } = node;
+    const { exported, scope: programScope } = this;
+
+    if (!t.isVariableDeclaration(left)) {
+      let didTransform = false;
+      const bodyPath = path.get("body");
+      const loopBodyScope = bodyPath.scope;
+      for (const name of Object.keys(t.getOuterBindingIdentifiers(left))) {
+        if (
+          exported.get(name) &&
+          programScope.getBinding(name) === scope.getBinding(name)
+        ) {
+          didTransform = true;
+          if (loopBodyScope.hasOwnBinding(name)) {
+            loopBodyScope.rename(name);
+          }
+        }
+      }
+      if (!didTransform) {
+        return;
+      }
+      const newLoopId = scope.generateUidIdentifierBasedOnNode(left);
+      bodyPath.unshiftContainer(
+        "body",
+        t.expressionStatement(t.assignmentExpression("=", left, newLoopId)),
+      );
+      path
+        .get("left")
+        .replaceWith(
+          t.variableDeclaration("let", [t.variableDeclarator(newLoopId)]),
+        );
+      scope.registerDeclaration(path.get("left"));
+    }
+  },
 };

packages/babel-plugin-transform-modules-commonjs/test/fixtures/misc/for-of-in-export/input.mjs

@@ -0,0 +1,22 @@
+export let foo;
+export {foo as bar}
+
+for (foo of []) {}
+for (foo in []) {}
+for (foo of []) {
+    let foo;
+}
+for ({foo} of []) {}
+for ({foo} of []) {
+    let foo;
+}
+for ({test: {foo}} of []) {}
+for ([foo, [...foo]] of []) {}
+for ([foo, [...foo]] of []) {
+    let foo;
+}
+
+{
+    let foo;
+    for(foo of []) {}
+}

packages/babel-plugin-transform-modules-commonjs/test/fixtures/misc/for-of-in-export/output.js

@@ -0,0 +1,65 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.bar = exports.foo = void 0;
+let foo;
+exports.bar = exports.foo = foo;
+
+for (let _foo of []) {
+  exports.bar = exports.foo = foo = _foo;
+}
+
+for (let _foo2 in []) {
+  exports.bar = exports.foo = foo = _foo2;
+}
+
+for (let _foo4 of []) {
+  exports.bar = exports.foo = foo = _foo4;
+
+  let _foo3;
+}
+
+for (let _foo5 of []) {
+  ({
+    foo
+  } = _foo5);
+  exports.bar = exports.foo = foo;
+}
+
+for (let _foo7 of []) {
+  ({
+    foo
+  } = _foo7);
+  exports.bar = exports.foo = foo;
+
+  let _foo6;
+}
+
+for (let _test of []) {
+  ({
+    test: {
+      foo
+    }
+  } = _test);
+  exports.bar = exports.foo = foo;
+}
+
+for (let _ref of []) {
+  [foo, [...foo]] = _ref;
+  exports.bar = exports.foo = foo;
+}
+
+for (let _ref2 of []) {
+  [foo, [...foo]] = _ref2;
+  exports.bar = exports.foo = foo;
+
+  let _foo8;
+}
+
+{
+  let foo;
+
+  for (foo of []) {}
+}