Prevent multiple return statements in a loop when replacing expressions (#5030)

packages/babel-plugin-transform-do-expressions/test/fixtures/do-expressions/while-if/actual.js

@@ -0,0 +1,10 @@
+let p
+let a = do {
+  while (p = p.parentPath) {
+    if (a) {
+      'a'
+    } else {
+      'b'
+    }
+  }
+};

packages/babel-plugin-transform-do-expressions/test/fixtures/do-expressions/while-if/expected.js

@@ -0,0 +1,13 @@
+let p;
+let a = function () {
+  var _ret;
+
+  while (p = p.parentPath) {
+    if (a) {
+      _ret = 'a';
+    } else {
+      _ret = 'b';
+    }
+  }
+  return _ret;
+}();

packages/babel-traverse/src/path/replacement.js

@@ -219,10 +219,16 @@ export function replaceExpressionWithStatements(nodes: Array<Object>) {
 
       const loop = path.findParent((path) => path.isLoop());
       if (loop) {
-        const callee = this.get("callee");
+        let uid = loop.getData("expressionReplacementReturnUid");
 
-        const uid = callee.scope.generateDeclaredUidIdentifier("ret");
+        if (!uid) {
-        callee.get("body").pushContainer("body", t.returnStatement(uid));
+          const callee = this.get("callee");
+          uid = callee.scope.generateDeclaredUidIdentifier("ret");
+          callee.get("body").pushContainer("body", t.returnStatement(uid));
+          loop.setData("expressionReplacementReturnUid", uid);
+        } else {
+          uid = t.identifier(uid.name);
+        }
 
         path.get("expression").replaceWith(
           t.assignmentExpression("=", uid, path.node.expression)