Transformation of static blocks breaks existing code

[lppedd]

Command

build

Is this a regression?

• [x] Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

No response

Description

It appears that when Angular compiles using a recent version of Babel's plugin-transform-class-static-block, with the Webpack builder, the output is transformed in such a way it breaks existing code.

Angular code compiled and bundled with @babel/[email protected]:

let CodeEditorWidget = class CodeEditorWidget extends _base_common_lifecycle_js__WEBPACK_IMPORTED_MODULE_5__.Disposable {
  static #_ = CodeEditorWidget_1 = this;
  static #_2 = this.dropIntoEditorDecorationOptions = _common_model_textModel_js__WEBPACK_IMPORTED_MODULE_27__.ModelDecorationOptions.register({
    description: 'workbench-dnd-target',
    className: 'dnd-target'
  }); //#endregion
  get isSimpleWidget() {
    return this._configuration.isSimpleWidget;
  }
  get contextMenuId() {
    return this._configuration.contextMenuId;
  }
  constructor(domElement, _options, codeEditorWidgetOptions, instantiationService, codeEditorService, commandService, contextKeyService, themeService, notificationService, accessibilityService, languageConfigurationService, languageFeaturesService) {
    var _this;
    super();
    _this = this;

   // Omitted for brevity
};

Angular code compiled and bundled with @babel/[email protected]:

let CodeEditorWidget = (class CodeEditorWidget extends _base_common_lifecycle_js__WEBPACK_IMPORTED_MODULE_5__.Disposable {                 
  //#endregion
  get isSimpleWidget() {
    return this._configuration.isSimpleWidget;
  }
  get contextMenuId() {
    return this._configuration.contextMenuId;
  }
  constructor(domElement, _options, codeEditorWidgetOptions, instantiationService, codeEditorService, commandService, contextKeyService, themeService, notificationService, accessibilityService, languageConfigurationService, languageFeaturesService) {
    var _this = this;
    super();

    // Omitted for brevity

  static #_ = _staticBlock = () => (CodeEditorWidget_1 = this, this.dropIntoEditorDecorationOptions = _common_model_textModel_js__WEBPACK_IMPORTED_MODULE_27__.ModelDecorationOptions.register({
    description: 'workbench-dnd-target',
    className: 'dnd-target'
  }), this);
}, _staticBlock());

The workaround, which you will also see explained in the attached reproducer, is to override the version of the Babel's plugin to 7.27.1.

I don't understand why, and under which circumstance, that plugin is injected into the compilation process.

Minimal Reproduction

Steps to reproduce can be found on the reproducer's repository: https://github.com/lppedd/angular-monaco-repro

Exception or Error

ERROR ReferenceError: Must call super constructor in derived class before accessing 'this' or returning from derived constructor
  at new CodeEditorWidget (codeEditorWidget.js:69:252)
  at new StandaloneCodeEditor (standaloneCodeEditor.js:69:9)
  at new StandaloneEditor (standaloneCodeEditor.js:188:9)
  at InstantiationService._createInstance (instantiationService.js:130:24)
  at InstantiationService.createInstance (instantiationService.js:101:27)
  at Object.create (standaloneEditor.js:43:33)
  at App.ngAfterViewInit (app.ts:16:33)
  at callHookInternal (debug_node.mjs:860:14)
  at callHook (debug_node.mjs:887:13)
  at callHooks (debug_node.mjs:841:17)

Your Environment

Angular CLI: 20.3.8
Node: 22.18.0
Package Manager: npm 11.6.2
OS: win32 x64
    

Angular: 20.3.9
... common, compiler, compiler-cli, core, forms
... platform-browser, router

Package                         Version
---------------------------------------
@angular-devkit/architect       0.2003.8
@angular-devkit/build-angular   20.3.8
@angular-devkit/core            20.3.8
@angular-devkit/schematics      20.3.8
@angular/build                  20.3.8
@angular/cli                    20.3.8
@schematics/angular             20.3.8
rxjs                            7.8.2
typescript                      5.9.3
zone.js                         0.15.1

Anything else relevant?

No response

[lppedd]

An alternative workaround seems to be patching @angular-devkit/build-angular.

diff --git a/node_modules/@angular-devkit/build-angular/src/tools/babel/presets/application.js b/node_modules/@angular-devkit/build-angular/src/tools/babel/presets/application.js
index 6063922..3128274 100644
--- a/node_modules/@angular-devkit/build-angular/src/tools/babel/presets/application.js
+++ b/node_modules/@angular-devkit/build-angular/src/tools/babel/presets/application.js
@@ -107,7 +107,7 @@ function default_1(api, options) {
                 bugfixes: true,
                 modules: false,
                 targets: options.supportedBrowsers,
-                exclude: ['transform-typeof-symbol'],
+                exclude: ['transform-typeof-symbol', 'transform-class-static-block'],
             },
         ]);
         needRuntimeTransform = true;

[lppedd]

The alternative workaround (patching @angular-devkit/build-angular) doesn't seem to work anymore with the latest 20.3.12, not sure why.

[lppedd]

Very important: after each Angular update + patch, the .angular cache directory must be removed.