JIT ɵɵngDeclareComponent defaults pre-v22 library components to OnPush; the AOT linker keeps them on Default (hasOnPushByDefault version rule is missing in convertDeclareComponentFacadeToMetadata) #71107

Which @angular/* package(s) are the source of the bug?

compiler

Is this a regression?

Yes

Description

A library compiled with Angular < 22 in partial compilation mode (ɵɵngDeclareComponent({ version: "20.3.x", ... })) whose component omits changeDetection is handled differently by the two consumers of that declaration in an Angular 22 application:

• AOT (partial linker) keeps it on Default/Eager: packages/compiler-cli/linker/src/file_linker/partial_linkers/partial_component_linker_1.ts computes hasOnPushByDefault = major >= 22 || version === PLACEHOLDER_VERSION and only then falls back to OnPush. That is correct: a component written for v20 was always checked and may assign state inside subscriptions or callbacks without markForCheck().
• JIT (ɵɵngDeclareComponent → ɵcompilerFacade.compileComponentDeclaration) ignores the declared version: packages/compiler/src/jit_compiler_facade.ts, convertDeclareComponentFacadeToMetadata, uses changeDetection: decl.changeDetection ?? ChangeDetectionStrategy.OnPush. The same v20 component becomes OnPush and silently stops re-rendering.

JIT is what Storybook (@storybook/angular), Jest (jest-preset-angular), Vitest without the AOT plugin, TestBed and ng serve --aot=false use, so a library that works in the built application breaks in every one of those. We hit it with Kendo UI for Angular 25 (compiled with Angular 20.3): its internal TreeViewGroupComponent assigns nodes inside a subscription and rendered an empty tree in Storybook, while the AOT build was fine.

This is the declare-path counterpart of #70262. That issue is about the JIT decorator path (@Component metadata → Eager) diverging from AOT (OnPush) for the app's own components. Here the JIT declare path (library partial declarations) diverges from the linker in the opposite direction: it applies the v22 default to declarations that predate v22. The two paths disagree with AOT in different ways, so fixing #70262 alone does not fix this.

Expected: the JIT declare path applies the same rule as the linker, i.e. OnPush only when decl.version is >= 22 (or the placeholder version), Eager otherwise.

Workaround we use in Storybook/Vitest (must run before any library declaration is evaluated):

import '@angular/compiler';
import { ChangeDetectionStrategy } from '@angular/core';

const facade = (globalThis as any).ng?.ɵcompilerFacade;
const original = facade.compileComponentDeclaration.bind(facade);
facade.compileComponentDeclaration = (env: unknown, url: string, decl: any) => {
  const major = Number.parseInt(String(decl.version ?? '0').split('.')[0], 10);
  const patched =
    decl.changeDetection == null && major > 0 && major < 22
      ? { ...decl, changeDetection: ChangeDetectionStrategy.Eager }
      : decl;
  return original(env, url, patched);
};

Please provide a link to a minimal reproduction of the bug

https://github.com/diegohoyos/angular-jit-onpush-repro

Please provide the exception or error you saw

No exception. The component compiled through ɵɵngDeclareComponent gets ɵcmp.onPush === true and its view is never refreshed after the subscription assigns new state.

Please provide the environment you discovered this bug in (run ng version)

Angular CLI       : 22.2.0
Angular           : 22.2.0
Node.js           : 22.23.2
Package Manager   : npm 12.0.2
Operating System  : win32 x64

┌───────────────────────────┬───────────────────┬───────────────────┐
│ Package                   │ Installed Version │ Requested Version │
├───────────────────────────┼───────────────────┼───────────────────┤
│ @angular/build            │ 22.2.0            │ 22.2.0            │
│ @angular/cli              │ 22.2.0            │ 22.2.0            │
│ @angular/common           │ 22.2.0            │ 22.2.0            │
│ @angular/compiler         │ 22.2.0            │ 22.2.0            │
│ @angular/compiler-cli     │ 22.2.0            │ 22.2.0            │
│ @angular/core             │ 22.2.0            │ 22.2.0            │
│ @angular/platform-browser │ 22.2.0            │ 22.2.0            │
│ rxjs                      │ 7.8.2             │ 7.8.2             │
│ typescript                │ 6.0.3             │ 6.0.3             │
│ zone.js                   │ 0.16.3            │ 0.16.3            │
└───────────────────────────┴───────────────────┴───────────────────┘

The library (legacy-lib) was compiled with @angular/compiler-cli 20.3.33 / typescript 5.8.3, compilationMode: "partial".

Anything else?

• packages/compiler-cli/linker/.../partial_component_linker_1.ts: const hasOnPushByDefault = major >= 22 || version === PLACEHOLDER_VERSION; then changeDetection: metaObj.has('changeDetection') ? ... : hasOnPushByDefault ? OnPush : Eager.
• packages/compiler/src/jit_compiler_facade.ts, convertDeclareComponentFacadeToMetadata: changeDetection: decl.changeDetection ?? ChangeDetectionStrategy.OnPush with no look at decl.version.
• Reproduces on 22.0.x through 22.2.0.