Class binding is in TDZ during decorators initialization

packages/babel-plugin-proposal-decorators/src/transformer-2023-05.ts

@@ -103,19 +103,20 @@ function createLazyPrivateUidGeneratorForClass(
  */
 function replaceClassWithVar(
   path: NodePath<t.ClassDeclaration | t.ClassExpression>,
-): [t.Identifier, NodePath<t.ClassDeclaration | t.ClassExpression>] {
+): {
+  id: t.Identifier;
+  path: NodePath<t.ClassDeclaration | t.ClassExpression>;
+  needsDeclaration: boolean;
+} {
   if (path.type === "ClassDeclaration") {
     const varId = path.scope.generateUidIdentifierBasedOnNode(path.node.id);
     const classId = t.identifier(path.node.id.name);
 
     path.scope.rename(classId.name, varId.name);
 
-    path.insertBefore(
-      t.variableDeclaration("let", [t.variableDeclarator(varId)]),
-    );
     path.get("id").replaceWith(classId);
 
-    return [t.cloneNode(varId), path];
+    return { id: t.cloneNode(varId), path, needsDeclaration: true };
   } else {
     let className: string;
     let varId: t.Identifier;
@@ -145,10 +146,11 @@ function replaceClassWithVar(
       t.sequenceExpression([newClassExpr, varId]),
     );
 
-    return [
-      t.cloneNode(varId),
-      newPath.get("expressions.0") as NodePath<t.ClassExpression>,
-    ];
+    return {
+      id: t.cloneNode(varId),
+      path: newPath.get("expressions.0") as NodePath<t.ClassExpression>,
+      needsDeclaration: false,
+    };
   }
 }
 
@@ -609,12 +611,15 @@ function transformClass(
     }
   };
 
+  let needsDeclaraionForClassBinding = false;
   if (classDecorators) {
     classInitLocal = scopeParent.generateDeclaredUidIdentifier("initClass");
 
-    const [classId, classPath] = replaceClassWithVar(path);
-    path = classPath;
-    classIdLocal = classId;
+    ({
+      id: classIdLocal,
+      path,
+      needsDeclaration: needsDeclaraionForClassBinding,
+    } = replaceClassWithVar(path));
 
     path.node.decorators = null;
 
@@ -1108,6 +1113,14 @@ function transformClass(
   // into a SequenceExpression
   path.insertBefore(assignments.map(expr => t.expressionStatement(expr)));
 
+  if (needsDeclaraionForClassBinding) {
+    path.insertBefore(
+      t.variableDeclaration("let", [
+        t.variableDeclarator(t.cloneNode(classIdLocal)),
+      ]),
+    );
+  }
+
   // Recrawl the scope to make sure new identifiers are properly synced
   path.scope.crawl();
 

packages/babel-plugin-proposal-decorators/test/fixtures/2021-12-classes/inheritance/output.js

@@ -1,7 +1,7 @@
 var _initClass, _dec, _initClass2, _dec2;
 const dec = () => {};
-let _Bar;
 _dec = dec1;
+let _Bar;
 class Bar {
   static {
     [_Bar, _initClass] = babelHelpers.applyDecs(this, [], [_dec]);
@@ -10,8 +10,8 @@ class Bar {
     _initClass();
   }
 }
-let _Foo;
 _dec2 = dec2;
+let _Foo;
 class Foo extends _Bar {
   static {
     [_Foo, _initClass2] = babelHelpers.applyDecs(this, [], [_dec2]);

packages/babel-plugin-proposal-decorators/test/fixtures/2021-12-exported/default-anonymous/output.mjs

@@ -1,6 +1,6 @@
 var _initClass, _dec;
-let _A;
 _dec = dec;
+let _A;
 class A {
   static {
     [_A, _initClass] = babelHelpers.applyDecs(this, [], [_dec]);

packages/babel-plugin-proposal-decorators/test/fixtures/2021-12-exported/default-named/output.mjs

@@ -1,6 +1,6 @@
 var _initClass, _dec;
-let _default2;
 _dec = dec;
+let _default2;
 class _default {
   static {
     [_default2, _initClass] = babelHelpers.applyDecs(this, [], [_dec]);

packages/babel-plugin-proposal-decorators/test/fixtures/2021-12-exported/named/output.mjs

@@ -1,6 +1,6 @@
 var _initClass, _dec;
-let _A;
 _dec = dec;
+let _A;
 class A {
   static {
     [_A, _initClass] = babelHelpers.applyDecs(this, [], [_dec]);

packages/babel-plugin-proposal-decorators/test/fixtures/2021-12-misc--to-es2015/valid-expression-formats/output.js

@@ -1,6 +1,5 @@
 var _initClass, _dec, _dec2, _dec3, _dec4, _dec5, _dec6, _dec7, _dec8, _initProto, _class;
 const dec = () => {};
-let _Foo;
 _dec = call();
 _dec2 = chain.expr();
 _dec3 = arbitrary + expr;
@@ -9,6 +8,7 @@ _dec5 = call();
 _dec6 = chain.expr();
 _dec7 = arbitrary + expr;
 _dec8 = array[expr];
+let _Foo;
 var _a = /*#__PURE__*/new WeakMap();
 class Foo {
   constructor(...args) {

packages/babel-plugin-proposal-decorators/test/fixtures/2021-12-misc/valid-expression-formats/output.js

@@ -1,6 +1,5 @@
 var _initClass, _dec, _dec2, _dec3, _dec4, _dec5, _dec6, _dec7, _dec8, _initProto;
 const dec = () => {};
-let _Foo;
 _dec = call();
 _dec2 = chain.expr();
 _dec3 = arbitrary + expr;
@@ -9,6 +8,7 @@ _dec5 = call();
 _dec6 = chain.expr();
 _dec7 = arbitrary + expr;
 _dec8 = array[expr];
+let _Foo;
 class Foo {
   static {
     [_initProto, _Foo, _initClass] = babelHelpers.applyDecs(this, [[[dec, _dec5, _dec6, _dec7, _dec8], 2, "method"]], [dec, _dec, _dec2, _dec3, _dec4]);

packages/babel-plugin-proposal-decorators/test/fixtures/2022-03-classes/inheritance/output.js

@@ -1,7 +1,7 @@
 var _initClass, _dec, _initClass2, _dec2;
 const dec = () => {};
-let _Bar;
 _dec = dec1;
+let _Bar;
 class Bar {
   static {
     [_Bar, _initClass] = babelHelpers.applyDecs2203R(this, [], [_dec]).c;
@@ -10,8 +10,8 @@ class Bar {
     _initClass();
   }
 }
-let _Foo;
 _dec2 = dec2;
+let _Foo;
 class Foo extends _Bar {
   static {
     [_Foo, _initClass2] = babelHelpers.applyDecs2203R(this, [], [_dec2]).c;

packages/babel-plugin-proposal-decorators/test/fixtures/2022-03-exported/default-anonymous/output.mjs

@@ -1,6 +1,6 @@
 var _initClass, _dec;
-let _A;
 _dec = dec;
+let _A;
 class A {
   static {
     [_A, _initClass] = babelHelpers.applyDecs2203R(this, [], [_dec]).c;

packages/babel-plugin-proposal-decorators/test/fixtures/2022-03-exported/default-named/output.mjs

@@ -1,6 +1,6 @@
 var _initClass, _dec;
-let _default2;
 _dec = dec;
+let _default2;
 class _default {
   static {
     [_default2, _initClass] = babelHelpers.applyDecs2203R(this, [], [_dec]).c;

packages/babel-plugin-proposal-decorators/test/fixtures/2022-03-exported/named/output.mjs

@@ -1,6 +1,6 @@
 var _initClass, _dec;
-let _A;
 _dec = dec;
+let _A;
 class A {
   static {
     [_A, _initClass] = babelHelpers.applyDecs2203R(this, [], [_dec]).c;

packages/babel-plugin-proposal-decorators/test/fixtures/2022-03-misc--to-es2015/valid-expression-formats/output.js

@@ -1,6 +1,5 @@
 var _initClass, _dec, _dec2, _dec3, _dec4, _dec5, _dec6, _dec7, _dec8, _initProto, _class;
 const dec = () => {};
-let _Foo;
 _dec = call();
 _dec2 = chain.expr();
 _dec3 = arbitrary + expr;
@@ -9,6 +8,7 @@ _dec5 = call();
 _dec6 = chain.expr();
 _dec7 = arbitrary + expr;
 _dec8 = array[expr];
+let _Foo;
 var _a = /*#__PURE__*/new WeakMap();
 class Foo {
   constructor(...args) {

packages/babel-plugin-proposal-decorators/test/fixtures/2022-03-misc/valid-expression-formats/output.js

@@ -1,6 +1,5 @@
 var _initClass, _dec, _dec2, _dec3, _dec4, _dec5, _dec6, _dec7, _dec8, _initProto;
 const dec = () => {};
-let _Foo;
 _dec = call();
 _dec2 = chain.expr();
 _dec3 = arbitrary + expr;
@@ -9,6 +8,7 @@ _dec5 = call();
 _dec6 = chain.expr();
 _dec7 = arbitrary + expr;
 _dec8 = array[expr];
+let _Foo;
 class Foo {
   static {
     ({

packages/babel-plugin-proposal-decorators/test/fixtures/2023-01-classes/inheritance/output.js

@@ -1,7 +1,7 @@
 var _initClass, _dec, _initClass2, _dec2;
 const dec = () => {};
-let _Bar;
 _dec = dec1;
+let _Bar;
 class Bar {
   static {
     [_Bar, _initClass] = babelHelpers.applyDecs2301(this, [], [_dec]).c;
@@ -10,8 +10,8 @@ class Bar {
     _initClass();
   }
 }
-let _Foo;
 _dec2 = dec2;
+let _Foo;
 class Foo extends _Bar {
   static {
     [_Foo, _initClass2] = babelHelpers.applyDecs2301(this, [], [_dec2]).c;

packages/babel-plugin-proposal-decorators/test/fixtures/2023-01-exported/default-anonymous/output.mjs

@@ -1,6 +1,6 @@
 var _initClass, _dec;
-let _A;
 _dec = dec;
+let _A;
 class A {
   static {
     [_A, _initClass] = babelHelpers.applyDecs2301(this, [], [_dec]).c;

packages/babel-plugin-proposal-decorators/test/fixtures/2023-01-exported/default-named/output.mjs

@@ -1,6 +1,6 @@
 var _initClass, _dec;
-let _default2;
 _dec = dec;
+let _default2;
 class _default {
   static {
     [_default2, _initClass] = babelHelpers.applyDecs2301(this, [], [_dec]).c;

packages/babel-plugin-proposal-decorators/test/fixtures/2023-01-exported/named/output.mjs

@@ -1,6 +1,6 @@
 var _initClass, _dec;
-let _A;
 _dec = dec;
+let _A;
 class A {
   static {
     [_A, _initClass] = babelHelpers.applyDecs2301(this, [], [_dec]).c;

packages/babel-plugin-proposal-decorators/test/fixtures/2023-01-misc--to-es2015/valid-expression-formats/output.js

@@ -1,6 +1,5 @@
 var _initClass, _dec, _dec2, _dec3, _dec4, _dec5, _dec6, _dec7, _dec8, _initProto, _class;
 const dec = () => {};
-let _Foo;
 _dec = call();
 _dec2 = chain.expr();
 _dec3 = arbitrary + expr;
@@ -9,6 +8,7 @@ _dec5 = call();
 _dec6 = chain.expr();
 _dec7 = arbitrary + expr;
 _dec8 = array[expr];
+let _Foo;
 var _a = /*#__PURE__*/new WeakMap();
 class Foo {
   constructor(...args) {

packages/babel-plugin-proposal-decorators/test/fixtures/2023-01-misc/valid-expression-formats/output.js

@@ -1,6 +1,5 @@
 var _initClass, _dec, _dec2, _dec3, _dec4, _dec5, _dec6, _dec7, _dec8, _initProto;
 const dec = () => {};
-let _Foo;
 _dec = call();
 _dec2 = chain.expr();
 _dec3 = arbitrary + expr;
@@ -9,6 +8,7 @@ _dec5 = call();
 _dec6 = chain.expr();
 _dec7 = arbitrary + expr;
 _dec8 = array[expr];
+let _Foo;
 class Foo {
   static {
     ({

packages/babel-plugin-proposal-decorators/test/fixtures/2023-05-classes/inheritance/output.js

@@ -1,7 +1,7 @@
 var _initClass, _dec, _initClass2, _dec2, _Bar2;
 const dec = () => {};
-let _Bar;
 _dec = dec1;
+let _Bar;
 class Bar {
   static {
     [_Bar, _initClass] = babelHelpers.applyDecs2305(this, [], [_dec]).c;
@@ -10,8 +10,8 @@ class Bar {
     _initClass();
   }
 }
-let _Foo;
 _dec2 = dec2;
+let _Foo;
 class Foo extends (_Bar2 = _Bar) {
   static {
     [_Foo, _initClass2] = babelHelpers.applyDecs2305(this, [], [_dec2], 0, void 0, _Bar2).c;

packages/babel-plugin-proposal-decorators/test/fixtures/2023-05-exported/default-anonymous/output.mjs

@@ -1,6 +1,6 @@
 var _initClass, _dec;
-let _A;
 _dec = dec;
+let _A;
 class A {
   static {
     [_A, _initClass] = babelHelpers.applyDecs2305(this, [], [_dec]).c;

packages/babel-plugin-proposal-decorators/test/fixtures/2023-05-exported/default-named/output.mjs

@@ -1,6 +1,6 @@
 var _initClass, _dec;
-let _default2;
 _dec = dec;
+let _default2;
 class _default {
   static {
     [_default2, _initClass] = babelHelpers.applyDecs2305(this, [], [_dec]).c;

packages/babel-plugin-proposal-decorators/test/fixtures/2023-05-exported/named/output.mjs

@@ -1,6 +1,6 @@
 var _initClass, _dec;
-let _A;
 _dec = dec;
+let _A;
 class A {
   static {
     [_A, _initClass] = babelHelpers.applyDecs2305(this, [], [_dec]).c;

packages/babel-plugin-proposal-decorators/test/fixtures/2023-05-misc--to-es2015/super-in-decorator/output.js

@@ -1,11 +1,11 @@
 class A extends B {
   m() {
     var _initClass, _obj, _dec, _obj2, _dec2, _initProto, _class;
-    let _C;
     _obj = this;
     _dec = super.dec1;
     _obj2 = this;
     _dec2 = super.dec2;
+    let _C;
     class C {
       constructor(...args) {
         _initProto(this);

packages/babel-plugin-proposal-decorators/test/fixtures/2023-05-misc--to-es2015/this/output.js

@@ -1,5 +1,4 @@
 var _initClass, _obj, _dec, _dec2, _obj2, _dec3, _obj3, _dec4, _obj4, _dec5, _init_x, _obj5, _dec6, _dec7, _init_y, _class;
-let _A;
 _obj = o1;
 _dec = _obj.dec;
 _dec2 = dec;
@@ -12,6 +11,7 @@ _dec5 = _obj4.dec;
 _obj5 = o2;
 _dec6 = _obj5.dec;
 _dec7 = dec;
+let _A;
 class A {
   constructor() {
     babelHelpers.defineProperty(this, "x", _init_x(this));

packages/babel-plugin-proposal-decorators/test/fixtures/2023-05-misc--to-es2015/valid-expression-formats/output.js

@@ -1,6 +1,5 @@
 var _initClass, _dec, _dec2, _dec3, _obj, _dec4, _dec5, _dec6, _dec7, _obj2, _dec8, _initProto, _class;
 const dec = () => {};
-let _Foo;
 _dec = call();
 _dec2 = chain.expr();
 _dec3 = arbitrary + expr;
@@ -11,6 +10,7 @@ _dec6 = chain.expr();
 _dec7 = arbitrary + expr;
 _obj2 = array;
 _dec8 = _obj2[expr];
+let _Foo;
 var _a = /*#__PURE__*/new WeakMap();
 class Foo {
   constructor(...args) {

packages/babel-plugin-proposal-decorators/test/fixtures/2023-05-misc/class-tdz-during-decorators/exec.js

@@ -0,0 +1,14 @@
+let didRun = false;
+
+function dec(fn) {
+  fn();
+  return () => {};
+}
+
+@dec(() => {
+  expect(() => Foo).toThrow(ReferenceError);
+  didRun = true;
+}) class Foo {}
+
+expect(didRun).toBe(true);
+