Fix export bindings not updated by 'for...in' and 'for...of' (#11074)

* 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"));
+    }
+  },
 };