Move the generator body to a gen IIFE when compiling its params

packages/babel-plugin-transform-async-to-generator/test/fixtures/regression/4943/output.js

@@ -7,11 +7,13 @@ function foo(_x) {
   return _foo.apply(this, arguments);
 }
 function _foo() {
-  _foo = babelHelpers.asyncToGenerator(function* (_ref) {
+  _foo = babelHelpers.asyncToGenerator(function (_ref) {
     let a = _ref.a,
       _ref$b = _ref.b,
       b = _ref$b === void 0 ? mandatory("b") : _ref$b;
-    return Promise.resolve(b);
+    return function* () {
+      return Promise.resolve(b);
+    }();
   });
   return _foo.apply(this, arguments);
 }

packages/babel-plugin-transform-parameters/src/params.ts

@@ -154,7 +154,7 @@ export default function convertFunctionParams(
   // ensure it's a block, useful for arrow functions
   path.ensureBlock();
 
-  if (state.needsOuterBinding || shadowedParams.size > 0) {
+  if (state.needsOuterBinding || shadowedParams.size > 0 || node.generator) {
     body.push(buildScopeIIFE(shadowedParams, path.node.body));
 
     path.set("body", t.blockStatement(body as t.Statement[]));

packages/babel-plugin-transform-parameters/test/fixtures/parameters/generator/input.ts

@@ -0,0 +1,6 @@
+function* fn(a, [], b = 2) {
+  yield a;
+  yield arguments;
+  yield this;
+  return b;
+}

packages/babel-plugin-transform-parameters/test/fixtures/parameters/generator/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["transform-parameters"]
+}

packages/babel-plugin-transform-parameters/test/fixtures/parameters/generator/output.js

@@ -0,0 +1,12 @@
+function fn(a, _ref) {
+  var _arguments = arguments,
+    _this = this;
+  let [] = _ref;
+  let b = arguments.length > 2 && arguments[2] !== undefined ? arguments[2] : 2;
+  return function* () {
+    yield a;
+    yield _arguments;
+    yield _this;
+    return b;
+  }();
+}

packages/babel-preset-env/test/fixtures/plugins-integration/issue-15012/exec.js

@@ -0,0 +1,13 @@
+function* f([]) {}
+
+expect(() => f()).toThrow();
+
+let called = false;
+let run = false;
+function* g(x = (called = true)) {
+  run = true;
+}
+
+g();
+expect(called).toBe(true);
+expect(run).toBe(false);

packages/babel-preset-env/test/fixtures/plugins-integration/issue-15012/input.js

@@ -0,0 +1,3 @@
+function* f([]) {}
+
+function* g(x = fn()) {}

packages/babel-preset-env/test/fixtures/plugins-integration/issue-15012/options.json

@@ -0,0 +1,3 @@
+{
+  "presets": ["env"]
+}

packages/babel-preset-env/test/fixtures/plugins-integration/issue-15012/output.js

@@ -0,0 +1,28 @@
+function f(_ref) {
+  var _ref2 = babelHelpers.toArray(_ref);
+  return /*#__PURE__*/babelHelpers.regeneratorRuntime().mark(function _callee() {
+    return babelHelpers.regeneratorRuntime().wrap(function _callee$(_context) {
+      while (1) {
+        switch (_context.prev = _context.next) {
+          case 0:
+          case "end":
+            return _context.stop();
+        }
+      }
+    }, _callee);
+  })();
+}
+function g() {
+  var x = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : fn();
+  return /*#__PURE__*/babelHelpers.regeneratorRuntime().mark(function _callee2() {
+    return babelHelpers.regeneratorRuntime().wrap(function _callee2$(_context2) {
+      while (1) {
+        switch (_context2.prev = _context2.next) {
+          case 0:
+          case "end":
+            return _context2.stop();
+        }
+      }
+    }, _callee2);
+  })();
+}