Bug 1950076 [wpt PR 50903] - [functions] Parameters with defaults need not be trailing (WPT), a=testonly

Automatic update from web-platform-tests
[functions] Parameters with defaults need not be trailing (WPT)

It's syntactically valid to define a function where a parameter without
a default appears after a parameter with a default, for example:

  @function --foo(--x:1px, --y, --z:2px) { ... }

There is currently no way to actually invoke such a function while
making use of the non-trailing defaults, but apparently this may change
in the future if we rework how IACVT works for arguments.
Invoking --foo(var(--unknown), 42px) would make the containing
declaration invalid at computed-value time, but in the future
the argument may "capture" this invalid state, and instead trigger
the default.

Bug: 389974127
Change-Id: I8d7c41bde2401ac89ec0a011f098e6051772f7b6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6281007
Commit-Queue: Anders Hartvoll Ruud <[email protected]>
Reviewed-by: Steinar H Gunderson <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1423827}

--

wpt-commits: f2615dc6260757b8eb634d19383184031c6e7022
wpt-pr: 50903

Author: andruud

testing/web-platform/tests/css/css-mixins/at-function-parsing.html

@@ -65,6 +65,10 @@
   test_valid_prelude('@function --foo(--x, --y <length>: 10px)');
   test_valid_prelude('@function --foo(--x type(<length> | auto): auto)');
   test_valid_prelude('@function --foo(--x type(<length> | auto) : auto)');
+  // A parameter without a default may appear after a parameter with
+  // a default, even though there's no way to actually call --foo()
+  // with just --y:
+  test_valid_prelude('@function --foo(--x:1px, --y, --z:2px)');
   // The value does not have to match the type during @function parsing:
   test_valid_prelude('@function --foo(--x <angle>: 10px)');
 

testing/web-platform/tests/css/css-mixins/dashed-function-eval.html

@@ -678,6 +678,20 @@
   </style>
 </template>
 
+<template data-name="Unknown var() in argument makes declaration IACVT">
+  <!-- Note: In the future, this may be changed to instead trigger
+             the default for --x. -->
+  <style>
+    @function --f(--x:1px) {
+      result: var(--x);
+    }
+    #target {
+      --actual: --f(var(--unknown));
+      /* --expected: <guaranteed-invalid> */
+    }
+  </style>
+</template>
+
 <!--
      {}-wrappers.