The problem is related to the implementation of font fallback on macOS,
specifically to the path used when text layout
is performed, i.e. the one using `FontSubstitution` and cascade lists.
`CTFontCopyDefaultCascadeListForLanguages`'s output contains an entry for the
font, able to render Armenian text ('NotoSansArmenian-Regular'), but
`CFont.createCompositeFont` cannot find this font amongst registered fonts, and
the entry is skipped, resulting in broken rendering.
System font loading (performed by `CFontManager.loadNativeFonts`) relies on
`[NSFontManager availableFontFamilies]`, but its output doesn't contain 'Noto
Sans Armenian' (which is a family for 'NotoSansArmenian-Regular' font). 'Noto
Sans Armenian' is recognized by `[NSFontManager availableMembersOfFontFamily:]`
though, 'NotoSansArmenian-Regular' is contained in `[NSFontManager
availableFonts]` output, and the font can be created and used normally, just
like any other system font. Not sure why its family is 'hidden', maybe macOS
developers wanted to limit the number of options
displayed in font selection drop-downs.
For reference, another cascade list item, ignored in similar way is
'NotoSansZawgyi-Regular'.
Proposed fix is to create `CFont` objects for cascade list items explicitly, if
corresponding fonts are not registered. These objects are re-used between
different fonts as their fallback components (to enable caching of
char-to-glyph mapping), but are not made available to public font APIs.
I've considered an alternative solution - using `[NSFontManager
availableFonts]` instead of
`[NSFontManager availableFontFamilies]` to load system fonts. Two factors
complicate it though - `loadNativeFonts` will
take more time (on my machine about 170 additional fonts will be loaded) and
the order of font loading will change (which
impacts the selection of 'preferred' plain/bold/italic/bolditalic components in
`FontFamily` class). Both factors can be
dealt with, but they make the solution more complicated and prone to
regressions. For now, it seems not worth it.
I've not created a test, as it would rely on macOS providing a fallback font
for Armenian script, which is not guaranteed.
Existing tests pass fine with the fix.
-------------
Commit messages:
- ensure all fallback components are used
Changes: https://git.openjdk.java.net/jdk/pull/6633/files
Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6633&range=00
Issue: https://bugs.openjdk.java.net/browse/JDK-8278050
Stats: 18 lines in 2 files changed: 16 ins; 0 del; 2 mod
Patch: https://git.openjdk.java.net/jdk/pull/6633.diff
Fetch: git fetch https://git.openjdk.java.net/jdk pull/6633/head:pull/6633
PR: https://git.openjdk.java.net/jdk/pull/6633
