[Webkit-unassigned] [Bug 271001] New: CSSOM serialization unexpectedly expands some shorthand properties

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=271001

            Bug ID: 271001
           Summary: CSSOM serialization unexpectedly expands some
                    shorthand properties
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebCore JavaScript
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: qianlangchen at apple.com

(See also https://webkit.org/b/75538 and https://webkit.org/b/73002, where this bug has been reported and a fix was attempted.)

The return values of `CSSRule.cssText` and `CSSStyleDeclaration.cssText` getters expand some shorthand CSS properties, specifically font-related shorthands like `font` or `font-variant`.

To reproduce, run this code in Safari inspector's console:
    s = new CSSStyleSheet(); 
    s.replaceSync('body { font: 12px serif; }'); 
    console.log(s.cssRules[0].cssText);

Observe that the output contains all the expanded longhand properties:
    body { font-style: normal; font-variant-caps: normal; font-weight: normal; font-stretch: normal; font-size: 12px; line-height: normal; font-family: serif; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-ligatures: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-position: normal; font-variant-emoji: normal; font-feature-settings: normal; font-optical-sizing: auto; font-variation-settings: normal; }

The expected output should just be
    body { font: 12px serif; }

The issue should be associated with how WebKit serializes a CSS declaration. The specs (https://drafts.csswg.org/cssom-1/#serialize-a-css-declaration-block), albeit very hard to read, suggest that shorthand properties should not be expanded and replaced with their longhand equivalents.

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