Add additional test coverage for CssOptimizer

The test failure confirms the suspected regression 😔

Alternative patch for #2 to verify that this fails on 10.0 too.

+++ b/core/tests/Drupal/FunctionalTests/Asset/RootRelativeUrlsInAggregatesTest.php
@@ -0,0 +1,50 @@
+    $css = $this->drupalGet($this->baseUrl . $href);

I think this is why this is a false alarm.

This is wrongly requesting a root-relative URL in $href prefixed by the base URL, which includes the hostname AND the subdirectory in which Drupal is installed.

Which is just plain wrong! 🙈

Unfortunately, \Drupal\Tests\UiHelperTrait::drupalGet() does not know how to follow links: it cannot handle root-relative URLs 😳 So we need this:

-    $css = $this->drupalGet($this->baseUrl . $href);
+    $parts = parse_url($this->baseUrl);
+    $scheme_and_host_of_base_url = sprintf("%s://%s", $parts['scheme'], $parts['host']);
+    $css = $this->drupalGet($scheme_and_host_of_base_url . $href);

Let's find out…

Correct patch.

Alternatively:

    $this->getSession()->visit($href);
    $css = $this->getSession()->getPage()->getContent();

… if #10 is green, then I'm going to close this. Sorry for the noise 🙈

I now wonder how this worked fine for about a decade 😅

I spent more time than I care to admit trying to make the test pass in so many different ways (every way I could think of to generate a file URL), didn't occur to me that the test might be broken!

Same thing here 😅🫣

However in the process of that, I did wonder if we should be doing this instead when building the asset URI.

Yes, we should! Query strings and fragments in url(…) references in CSS files is one of the things that has been causing bug reports against the CDN module for over a decade:

1. #1514182: IE @font-face CSS hack URL broken by CDN module's overridden CSS aggregation
2. #1978170: CSS aggregation override breaks querystrings of referenced files
3. #3128116: Negated file extensions in file URLs with querystrings or fragments are not recognized correctly

And I think \Drupal\Tests\cdn\Unit\File\FileUrlGeneratorTest::urlProvider() now provides a pretty solid/comprehensive set of test cases: https://git.drupalcode.org/project/cdn/-/blob/4.0.1/tests/src/Unit/File/.... We'd want to change that to not be CDN-simulated of course, but other than that, if we'd test a CSS file containing every edge case listed there, we'd be better off for sure.

The urldecode is extremely annoying though, so we might want a follow-up for that bit.

Hah, that is that other edge case which has seen many bug reports over the years, but I can only quickly find this one: #1719568: CDN URLs are not properly encoded in some edge cases.

That too is covered by that same test case I just linked 😊

@catch Would you be interested in me porting that test coverage to core?