[Webkit-unassigned] [Bug 234094] New: Layered @import rules in <style> should be preloaded

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Thu Dec 9 11:28:34 PST 2021


            Bug ID: 234094
           Summary: Layered @import rules in <style> should be preloaded
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CSS
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: xiaochengh at chromium.org

Created attachment 446576

  --> https://bugs.webkit.org/attachment.cgi?id=446576&action=review

layered imports not preloaded

Test case: https://purring-various-felidae.glitch.me/css-import-preload-layer.html

It tests if the following CSS imports are preloaded:

  @import url('/stylesheet?delay=1001');
  @import url('/stylesheet?delay=1002') layer;
  @import url('/stylesheet?delay=1003') layer(foo);

(Here delay=foo means the request takes foo ms to finish)

All the three should be preloaded, but as I tested in Safari Technology Preview Release 135 (Safari 15.4, WebKit 17613.1.7.3), the two layered imports are not preloaded. They start loading only after the parser-blocking script have finished, as shown by the attached screenshot.

This will hurt the loading performance when using cascade layers, since @import is currently the only way to add an external stylesheet into a layer.

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