[Fontconfig-bugs] [Bug 94505] New: Writing name.preferredFamilyname of a font in <prefer> tag messes up with name.font{, sub}Family

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=94505

            Bug ID: 94505
           Summary: Writing name.preferredFamilyname of a font in <prefer>
                    tag messes up with name.font{,sub}Family
           Product: fontconfig
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: library
          Assignee: fontconfig-bugs at lists.freedesktop.org
          Reporter: arthur200126 at gmail.com
        QA Contact: freedesktop at behdad.org

Many True/OpenType fonts, like Noto Sans CJK ("notocjk") in this example, uses
a pattern in "name" table where:

* name.fontFamily gives the full name (with style) of the font and Subfamily is
always Regular
* name.preferredFamily gives the actual family name and Subfamily is the actual
weight

Fontconfig doesn't seem to be capable of handling such a case. Specifically,
given a config file which <prefer>s notocjk:

        <alias>
                <family>sans-serif</family>
                <prefer>
                        <family>Noto Sans CJK SC</family>
                        <family>Noto Sans CJK TC</family>
                </prefer>
        </alias>

Fontconfig will produce a match like:

$ fc-match --verbose
Pattern has 38 elts (size 48)
        family: "Noto Sans CJK SC"(s) "Noto Sans CJK SC DemiLight"(s)
        familylang: "en"(s) "en"(s)
        style: "DemiLight"(w) "Regular"(w)
        stylelang: "en"(w) "en"(w)
        fullname: "Noto Sans CJK SC DemiLight"(w)
        fullnamelang: "en"(w)
        [...]

Now here is the problem. By preferring the preferredFamily "Noto Sans CJK SC",
fontconfig ended up also preferring "Noto Sans CJK SC DemiLight", and matched
"Noto Sans CJK SC DemiLight" "Regular" for the implicit "Regular".

See https://bugs.launchpad.net/ubuntu/+source/language-selector/+bug/1468027
for a context of this problem.

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