[wp-trac] [WordPress Trac] #65080: wp_admin_bar_add_color_scheme_to_front_end()` uses `wp_remote_get()` to fetch a local CSS file, causing an unnecessary HTTP request on every front-end page load

[WordPress Trac]

#65080: wp_admin_bar_add_color_scheme_to_front_end()` uses `wp_remote_get()` to
fetch a local CSS file, causing an unnecessary HTTP request on every front-
end page load
--------------------------+-----------------------------
 Reporter:  edumembe      |      Owner:  (none)
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  HTTP API      |    Version:  trunk
 Severity:  normal        |   Keywords:  needs-patch
  Focuses:  performance   |
--------------------------+-----------------------------
 **Description:**

 The function introduced in 7.0.0 (`wp-includes/admin-bar.php`) fetches the
 admin color scheme stylesheet via `wp_remote_get( $url )`, where `$url`
 points to a local file such as `/wp-
 admin/css/colors/modern/colors.min.css`.

 This results in a full HTTP round-trip to the server itself on every
 front-end page load when the admin bar is visible. On our test
 environment, this request consistently takes ~30ms, accounting for the
 majority of the performance difference between WordPress 6.9 and 7.0.

 **Steps to reproduce:**
 1. Install WordPress 7.0 with any classic theme.
 2. Log in as an administrator and visit the front end.
 3. Open Query Monitor → HTTP API Calls.
 4. Observe a GET request to `/wp-admin/css/colors/modern/colors.min.css`
 taking 20–50ms.

 **Expected behavior:**
 The CSS content should be read directly from the filesystem using
 `file_get_contents()` or `WP_Filesystem`, avoiding the HTTP overhead
 entirely. The file path is already resolvable locally via `ABSPATH`.

 **Suggested fix:**
 Replace `wp_remote_get( $url )` with a direct filesystem read:

 ```php
 $css_file = ABSPATH . 'wp-admin/css/colors/' . $color_scheme .
 '/colors.min.css';
 if ( ! file_exists( $css_file ) ) {
     return;
 }
 $css = file_get_contents( $css_file );
 ```

 This eliminates the HTTP request while producing identical output.

 **Environment:**
 - WordPress 7.0
 - Classic (non-block) theme
 - Admin bar enabled on front end
 - PHP 8.x, OPcache enabled

 **Impact:** Performance regression on every front-end page load for
 logged-in users. The HTTP request is blocking and adds 20–50ms of latency
 unconditionally.

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Ticket URL: <https://core.trac.wordpress.org/ticket/65080>
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