[Webkit-unassigned] [Bug 234342] New: Letter-spacing & first-letter selection must keep yo-phola with preceding independent vowels

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=234342

            Bug ID: 234342
           Summary: Letter-spacing & first-letter selection must keep
                    yo-phola with preceding independent vowels
           Product: WebKit
           Version: Safari 15
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CSS
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: ishida at w3.org

There are two cases in Bengali where hasant (virama) is preceded by an independent vowel, rather than a consonant. These are:

    অ্যা [U+0985 BENGALI LETTER A + U+09CD BENGALI SIGN VIRAMA + U+09AF BENGALI LETTER YA + U+09BE BENGALI VOWEL SIGN AA], and
    এ্যা [U+098F BENGALI LETTER E + U+09CD BENGALI SIGN VIRAMA + U+09AF BENGALI LETTER YA + U+09BE BENGALI VOWEL SIGN AA]

Illustrations:
https://user-images.githubusercontent.com/4839211/146041054-f96714a2-b926-4ea4-8e17-ba4e003a671e.png

https://user-images.githubusercontent.com/4839211/146041082-fbdd1cee-1bdc-4c45-b2d8-d427b8027c77.png

https://user-images.githubusercontent.com/4839211/146041100-ab30d934-2a22-4e2e-9c6e-68cb3965f3e9.png

(In both cases this produces the sound æ, used for non-native words, such as 'application', 'administration' etc.)

This combination should not be split either, even though it doesn't fit the typical CvC structure of a conjunct (where 'v' is the virama).


Tests & results:
Both of the following tests were run with the following pre-installed fonts:

Windows: Shonar Bangla, Arial Unicode MS, Nirmala UI, Vrinda

Mac: Bangla MN, Bangla Sangam MN, Kohinoor Bangla, Tiro Bangla, Baloo Da

Also tested with Noto Sans Bengali and Noto Serif Bengali on the Mac.

Interactive test, Bengali অ্যা and এ্যা (æ) are selected as a single grapheme by ::first-letter. https://github.com/w3c/line_paragraph_tests/issues/80

    Gecko: ✅❌ Mac: fails for Bangla MN, and Bangla Sangam MN, but passes for the other 3 fonts. Windows: works fine for all fonts.
    Blink: ❌ Mac & Windows: fails for all fonts.
    Webkit: ❌ Mac: fails for all fonts. It was not possible to apply the Noto fonts.

Note that Blink and Webkit actually handle the more usual CvC conjunct arrangement (see this test).

Interactive test, Bengali অ্যা and এ্যা (æ) are treated as a single grapheme for letter-spacing.  https://github.com/w3c/line_paragraph_tests/issues/81

    Gecko: ✅❌ Windows: works with all fonts. Mac: fails with Bangla MN, Bangla Sangam MN, and Baloo Da, but works with the others. Works with Noto fonts.
    Blink: ✅❌ Windows: works with all fonts. Mac: same results as for Gecko.
    Webkit: ❌ Mac: failed for all fonts. In fact, letters were all spaced individually, rather than by grapheme cluster. Could not apply Noto fonts.

Gecko, Blink, and Webkit all fail to treat the sequence as a single grapheme, despite the fact that Blink and Webkit actually handle the more usual CvC conjunct arrangement (see this test).

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