Fixes#20433.
The warning filter in `optimize.ts` already ignores `:deep()`,
`:slotted()` and `:global()`. Angular's two deep selectors are the same
kind of thing — non-standard pseudo-selectors that the framework's
compiler resolves before the CSS reaches a browser — but they aren't
covered, so every Angular component stylesheet using them prints a
warning block per occurrence.
```
Found 2 warnings while optimizing generated CSS:
Issue #1:
│ :host ::ng-deep .some-child, :host
┆ ^-- 'ng-deep' is not recognized as a valid pseudo-element. Did you mean ':ng-deep' (pseudo-class) or is this a typo?
```
Angular strips both during view-encapsulation shimming — `::ng-deep` via
`_shadowDeepSelectors = /(?:>>>)|(?:\/deep\/)|(?:::ng-deep)/g`, and
`:host-context()` in the same pass — so neither ever reaches a browser.
Worth noting that `/deep/` and `>>>`, Angular's two other spellings of
the deep selector, already pass silently because
`nonStandard.deepSelectorCombinator` is enabled. `::ng-deep` is the only
one that warns, and it's the spelling the Angular docs use — so in
practice every Angular codebase hits this. On the workspace where I ran
into it (7 Angular apps), a production build printed 425 `ng-deep`
warnings and 2 `host-context` ones.
## Test plan
There's no automated coverage here because the warning path is behind
`process.env.NODE_ENV !== 'test'`, so a spy sees nothing under Vitest
regardless of the filter — the same reason #20277 shipped without one.
Instead I ran the file before and after the change against Lightning CSS
1.33.0 directly, counting emitted warning blocks:
| Input | Before | After |
| --- | --- | --- |
| `:host ::ng-deep .a, :host ::ng-deep .b { … }` | 1 | 0 |
| `:host-context(.dark) .a { … }` | 1 | 0 |
| `:deep(.a) { … }` | 0 | 0 |
| `.a::totally-not-real { … }` — genuine typo | 1 | **1** |
Generated CSS is byte-identical before and after; only the warning is
suppressed. Genuine unknown pseudo-selectors still warn, so the typo
hint the message exists for is preserved.
Happy to restructure this if you'd prefer the predicate extracted so it
can be unit-tested, or to split `ng-deep` and `host-context` into their
own block rather than extending the existing regex.
A minimal reproduction of the original issue is at
https://gist.github.com/weilinzung/ace42ceb95c2f47b6747cc1f34f162bd.
---------
Co-authored-by: Robin Malfait <malfait.robin@gmail.com>
f723e834ad