`-webkit-` prefix removed from `backdrop-filter` even though Safari needs it

[schuetzm]

Safari doesn't support unprefixed backdrop-filter:
https://caniuse.com/css-backdrop-filter

Unfortunately, LightningCSS removes the necessary -webkit- prefix when both the prefixed and the normal version are used:
Playground

Funnily enough, if there's only an unprefixed backdrop-filter, it outputs both the prefixed and the unprefixed version:
Playground

I would expect both inputs to result in the same output including both the prefixed and unprefixed declaration.

[christianmartinnies]

I observe the exact opposite behaviour as it is added twice after a build.

Source:

dialog::backdrop {
  opacity: 1;
  backdrop-filter: blur(0.125rem);
}

Build:

dialog::backdrop {
  opacity: 1;
  -webkit-backdrop-filter: blur(0.125rem);
  -webkit-backdrop-filter: blur(0.125rem);
  backdrop-filter: blur(0.125rem);
}

[LeoniePhiline]

Previously duplicated -webkit-backdrop-filter rules now completely removed: Regression in lightningcss 1.21.0 (diff)

All results produced with pnpm exec lightningcss --targets 'defaults' input.css -o output.css after pnpm i -D lightningcss@1.20.0 / pnpm i -D lightningcss@1.21.0.

The following duplicates -webkit-backdrop-filter rules (minor inconvenience) with lightningcss 1.20.1 and completely removes -webkit-backdrop-filter rules (breaking Safari compatibility) with lightningcss 1.21.0:

Source

Side note: This source is parcel output. Parcel, invoked with --no-optimize added the autoprefixed line.
This parcel output is now sent through lightningcss-cli to simulate use of @parcel/optimizer-css.

.cc-bottom {
  -webkit-backdrop-filter: saturate(250%) blur(8px);
  backdrop-filter: saturate(250%) blur(8px);
}

Good result in lightningcss 1.20.0 and below

The duplicated -webkit-backdrop-filter line is a nuissance, but does not break anything.
#403 reports this duplication.

.cc-bottom {
  -webkit-backdrop-filter: saturate(250%) blur(8px);
  -webkit-backdrop-filter: saturate(250%) blur(8px);
  backdrop-filter: saturate(250%) blur(8px);
}

Bad result in lightningcss 1.21.0+ (diff)

The missing -webkit-backdrop-filter line breaks Safari compatibility.
#537 reports the incorrectly removed prefixed lines.

.cc-bottom {
  backdrop-filter: saturate(250%) blur(8px);
}

Missing tests

Added failing test: https://github.com/parcel-bundler/lightningcss/pull/553/files#diff-b1a35a68f14e696205874893c07fd24fdb88882b47c23cc0e0c80a30c7d53759R12798-R12816

Initial analysis

Auto-generated src/prefixes.rs is correct, with 589824 indicating "Safari 9.0.0 and higher", and no upper bound:

https://github.com/parcel-bundler/lightningcss/blob/master/src/prefixes.rs#L557-L562

[jur-ng]

On the latest version (1.22.0) I now see the following behavior:

source:

.toast {  
     backdrop-filter: blur(30px) !important;
    -webkit-backdrop-filter: blur(30px) !important;
}

result:

.d7fzDW_toast {
  -webkit-backdrop-filter: blur(30px) !important;
}

And source:

.toast {  
     backdrop-filter: blur(30px) !important;
}

result:

.d7fzDW_toast {
    backdrop-filter: blur(30px) !important;
}

So basically the non-prefixed version is removed when I also include the -webkit prefixed one, and the webkit prefixed one is not autimatically added when I have just the non-prefixed one :/

EDIT As a workaround I now downgraded to 1.20.0 as having two -webkit-backdrop-filters is better than having one or having it remove the normal backdrop-filter. Could you maybe look into this though @LeoniePhiline ?

EDIT2 It does not happen in the playground so I guess this might have something to do with my default Vite config? I only enabled CSS modules.

EDIT3 Nope it definitely seems like a bug when no target is specified, you can check the difference in this playground between 1.22.0 and 1.20.0

[brycewray]

FWIW, observing the same with filter vs. -webkit-filter and have also tested in the playground to which @jur-ng linked above.

[LeoniePhiline]

@brycewray This issue is closed. Try opening a new one, with a repro project and/or link to a repro in the playground.