Selector: Make selector lists work with `qSA` again

jQuery 3.6.2 started using `CSS.supports( "selector(SELECTOR)" )` before using
`querySelectorAll` on the selector. This was to solve gh-5098 - some selectors,
like `:has()`, now had their parameters parsed in a forgiving way, meaning
that `:has(:fakepseudo)` no longer throws but just returns 0 results, breaking
that jQuery mechanism.

A recent spec change made `CSS.supports( "selector(SELECTOR)" )` always use
non-forgiving parsing, allowing us to use this API for what we've used
`try-catch` before.

To solve the issue on the spec side for older jQuery versions, `:has()`
parameters are no longer using forgiving parsing in the latest spec update
but our new mechanism is more future-proof anyway.

However, the jQuery implementation has a bug - in
`CSS.supports( "selector(SELECTOR)" )`, `SELECTOR` needs to be
a `<complex-selector>` and not a `<complex-selector-list>`. Which means that
selector lists now skip `qSA` and go to the jQuery custom traversal:
```js
CSS.supports("selector(div:valid, span)"); // false
CSS.supports("selector(div:valid)"); // true
CSS.supports("selector(span)"); // true
```

To solve this, this commit wraps the selector list passed to
`CSS.supports( "selector(:is(SELECTOR))" )` with `:is`, making it a single
selector again.

See:
* https://w3c.github.io/csswg-drafts/css-conditional-4/#at-supports-ext
* https://w3c.github.io/csswg-drafts/selectors-4/#typedef-complex-selector
* https://w3c.github.io/csswg-drafts/selectors-4/#typedef-complex-selector-list

Fixes gh-5177
Closes gh-5178
Ref w3c/csswg-drafts#7280

1 files changed, 21 insertions, 1 deletions

diff --git a/test/unit/selector.js b/test/unit/selector.js
index 0057fe57a..d177ab997 100644
--- a/test/unit/selector.js
+++ b/test/unit/selector.js
@@ -400,7 +400,7 @@ QUnit.test( "name", function( assert ) {
 } );
 
 QUnit.test( "comma-separated", function( assert ) {
-	assert.expect( 4 );
+	assert.expect( 10 );
 
 	var fixture = jQuery( "<div><h2><span></span></h2><div><p><span></span></p><p></p></div></div>" );
 
@@ -408,6 +408,26 @@ QUnit.test( "comma-separated", function( assert ) {
 	assert.equal( fixture.find( "h2, div p" ).filter( "h2" ).length, 1, "has to find one <h2>" );
 	assert.equal( fixture.find( "h2 , div p" ).filter( "p" ).length, 2, "has to find two <p>" );
 	assert.equal( fixture.find( "h2 , div p" ).filter( "h2" ).length, 1, "has to find one <h2>" );
+	assert.equal( fixture.find( "h2 ,div p" ).filter( "p" ).length, 2, "has to find two <p>" );
+	assert.equal( fixture.find( "h2 ,div p" ).filter( "h2" ).length, 1, "has to find one <h2>" );
+	assert.equal( fixture.find( "h2,div p" ).filter( "p" ).length, 2, "has to find two <p>" );
+	assert.equal( fixture.find( "h2,div p" ).filter( "h2" ).length, 1, "has to find one <h2>" );
+	assert.equal( fixture.find( "h2\t,\rdiv p" ).filter( "p" ).length, 2, "has to find two <p>" );
+	assert.equal( fixture.find( "h2\t,\rdiv p" ).filter( "h2" ).length, 1, "has to find one <h2>" );
+} );
+
+QUnit.test( "comma-separated, only supported natively (gh-5177)", function( assert ) {
+	assert.expect( 5 );
+
+	var fixture = jQuery( "<div><input/><span></span></div>" );
+
+	fixture.appendTo( "#qunit-fixture" );
+
+	assert.equal( fixture.find( "input:valid, span" ).length, 2, "has to find two elements" );
+	assert.equal( fixture.find( "input:valid , span" ).length, 2, "has to find two elements" );
+	assert.equal( fixture.find( "input:valid ,span" ).length, 2, "has to find two elements" );
+	assert.equal( fixture.find( "input:valid,span" ).length, 2, "has to find two elements" );
+	assert.equal( fixture.find( "input:valid\t,\rspan" ).length, 2, "has to find two elements" );
 } );
 
 QUnit.test( "child and adjacent", function( assert ) {