incorrect handling of returns nested in switch cases (#3618)

packages/babel-plugin-transform-es2015-block-scoping/src/index.js

@@ -684,11 +684,13 @@ class BlockScoping {
           single.consequent[0]
         ));
       } else {
-        // https://github.com/babel/babel/issues/998
-        for (let i = 0; i < cases.length; i++) {
-          let caseConsequent = cases[i].consequent[0];
-          if (t.isBreakStatement(caseConsequent) && !caseConsequent.label) {
-            caseConsequent.label = this.loopLabel = this.loopLabel || this.scope.generateUidIdentifier("loop");
+        if (this.loop) {
+          // https://github.com/babel/babel/issues/998
+          for (let i = 0; i < cases.length; i++) {
+            let caseConsequent = cases[i].consequent[0];
+            if (t.isBreakStatement(caseConsequent) && !caseConsequent.label) {
+              caseConsequent.label = this.loopLabel = this.loopLabel || this.scope.generateUidIdentifier("loop");
+            }
           }
         }
 

packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/superswitch/actual.js

@@ -0,0 +1,16 @@
+function foo() {
+  switch (2) {
+    case 0: {
+      if (true) {
+        return;
+      }
+
+      const stuff = new Map();
+      const data = 0;
+      stuff.forEach(() => {
+        const d = data;
+      });
+      break;
+    }
+  }
+}

packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/superswitch/expected.js

@@ -0,0 +1,29 @@
+function foo() {
+  switch (2) {
+    case 0:
+      {
+        var _ret = function () {
+          if (true) {
+            return {
+              v: void 0
+            };
+          }
+
+          var stuff = new Map();
+          var data = 0;
+          stuff.forEach(function () {
+            var d = data;
+          });
+          return "break";
+        }();
+
+        switch (_ret) {
+          case "break":
+            break;
+
+          default:
+            if (typeof _ret === "object") return _ret.v;
+        }
+      }
+  }
+}