fix #1498: variable shadowing broke class lowering

CHANGELOG.md

@@ -59,6 +59,28 @@
     }
     ```
 
+* Fix lowering of static private methods in class expressions ([#1498](https://github.com/evanw/esbuild/issues/1498))
+
+    Previously static private methods were lowered incorrectly when present in class expressions. The class expression itself was missing in the output due to an oversight (variable shadowing). This issue has been fixed:
+
+    ```js
+    // Original code
+    (class {
+      static #x() {}
+    });
+
+    // Old output (with --target=es6)
+    var _x, _a, x_fn;
+    __privateAdd(_a, _x), _x = new WeakSet(), x_fn = function() {
+    }, __privateAdd(_a, _x), _a;
+
+    // New output (with --target=es6)
+    var _x, _a, x_fn;
+    _a = class {
+    }, _x = new WeakSet(), x_fn = function() {
+    }, __privateAdd(_a, _x), _a;
+    ```
+
 ## 0.12.17
 
 * Fix a bug with private fields and logical assignment operators ([#1418](https://github.com/evanw/esbuild/issues/1418))

internal/bundler/snapshots/snapshots_lower.txt

@@ -335,7 +335,17 @@ _foo = new WeakMap();
 TestLowerPrivateClassExpr2020NoBundle
 ---------- /out.js ----------
 var _field, _method, method_fn, _a, _staticField, _staticMethod, staticMethod_fn;
-export let Foo = (__privateAdd(_a, _staticMethod), _field = new WeakMap(), _method = new WeakSet(), method_fn = function() {
+export let Foo = (_a = class {
+  constructor() {
+    __privateAdd(this, _method);
+    __privateAdd(this, _field, void 0);
+  }
+  foo() {
+    var _a2;
+    __privateSet(this, _field, __privateMethod(this, _method, method_fn).call(this));
+    __privateSet(Foo, _staticField, __privateMethod(_a2 = Foo, _staticMethod, staticMethod_fn).call(_a2));
+  }
+}, _field = new WeakMap(), _method = new WeakSet(), method_fn = function() {
 }, _staticField = new WeakMap(), _staticMethod = new WeakSet(), staticMethod_fn = function() {
 }, __privateAdd(_a, _staticMethod), __privateAdd(_a, _staticField, void 0), _a);
 

internal/js_parser/js_parser_lower.go

@@ -2269,7 +2269,7 @@ func (p *parser) lowerClass(stmt js_ast.Stmt, expr js_ast.Expr, shadowRef js_ast
 					}
 
 					// Add every newly-constructed instance into this map
-					expr = p.callRuntime(loc, "__privateAdd", []js_ast.Expr{
+					methodExpr := p.callRuntime(loc, "__privateAdd", []js_ast.Expr{
 						target,
 						{Loc: loc, Data: &js_ast.EIdentifier{Ref: ref}},
 					})
@@ -2285,10 +2285,10 @@ func (p *parser) lowerClass(stmt js_ast.Stmt, expr js_ast.Expr, shadowRef js_ast
 					//
 					if prop.IsStatic {
 						// Move this property to an assignment after the class ends
-						staticPrivateMethods = append(staticPrivateMethods, expr)
+						staticPrivateMethods = append(staticPrivateMethods, methodExpr)
 					} else {
 						// Move this property to an assignment inside the class constructor
-						instancePrivateMethods = append(instancePrivateMethods, js_ast.Stmt{Loc: loc, Data: &js_ast.SExpr{Value: expr}})
+						instancePrivateMethods = append(instancePrivateMethods, js_ast.Stmt{Loc: loc, Data: &js_ast.SExpr{Value: methodExpr}})
 					}
 				}