Intermittent crash on startup with zh_TW/zh_CN locale and empty workspace (libSkiaSharp TTC font bug)

[JC-Chung]

工作區沒有任何存放庫且語言為中文時有機會打不開 `SourceGit
早上/下午能持續重現問題，但像發文前的現在又都能正常開啟
有試過問題發生時中文以外都能正常開啟

另外 Locale 沒有對應語言時 UI 會沒顯示任何文字，是否 fallback 到 en_US 會比較好

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Steps to Reproduce

1. Set Locale to zh_TW or zh_CN in preference.json
2. Ensure Workspaces[0].Repositories is an empty array []
3. Launch SourceGit.exe

Expected: Application opens normally.

Actual: The process appears briefly in Task Manager and immediately disappears. No crash log is generated. The behavior is intermittent — rapid repeated launches occasionally succeed. Deleting data/process.lock before launching does not reliably fix the issue. The problem does not occur with any other locale.

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Environment

• SourceGit: v2026.15 (7149a8d70c), and intermittently in v2026.14 (see below)
• Build: Official release (Native AOT, .NET 10.0.301, win-x64)
• Avalonia: 11.3.18 → SkiaSharp 2.88.9 (Skia m88)
• OS: Windows

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Affected Commits in v2026.14

The issue was observed between:

• 34f4a7c6f2 — refactor: use * instead *.* to choose file without specified extensions (2026-07-02)
• 222cd80272 — ux: use Ctrl/⌘+W to close sub-windows (2026-07-06)

The crash was not reproduced after 7327ccd266 (localization: update Chinese translations, 2026-07-06), though this may simply be due to the intermittent nature of the bug. It reappeared in v2026.15 (7149a8d70c).

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* Guess

Root Cause

Analyzed via x64dbg on the official release binary.

The crash occurs on the Avalonia render thread — not the main thread — which is why .NET's UnhandledException handler is never triggered and no crash log is produced.

Crash location: libSkiaSharp.dll offset 0x4ABE05
Instruction: mov rax, qword ptr ds:[rcx] (rcx = 0x0)
Exception: EXCEPTION_ACCESS_VIOLATION (last-chance)

Call stack:

1. libSkiaSharp.dll — TTC font parsing (crash)
2. SourceGit.exe — P/Invoke wrapper for sk_stream_read
3. SourceGit.exe — Avalonia render/layout traversal

When Avalonia's render thread calls SKFontManager.MatchCharacter() to find a font for Chinese characters, it goes through the DirectWrite font manager (SkFontMgr_win_dw.cpp). On a cache miss, DirectWrite performs lazy loading of TTC font data. During this, an internal function sets the stream pointer to null, but the caller still tries to use it — null pointer dereference.

Why only zh_TW/zh_CN: Chinese system fonts (mingliu.ttc, msjh.ttc, etc.) are almost exclusively TTC format. Other locales use single TTF files and don't hit this path.

Why intermittent: TTC fonts have a cache. Cache hits skip full parsing (no crash); cache misses trigger the full TTC parsing path (crash).

Why only with empty repositories: When repositories are open, other UI elements appear to pre-warm the font cache before the problematic render path is reached. With only the Welcome page shown, the cache miss occurs at a critical moment.

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SkiaSharp / Skia Context

Avalonia	SkiaSharp	Skia milestone
11.3.18 (current)	2.88.9	m88
12.0.4 / 12.1.0	3.119.4	m119

The DirectWrite font manager was refactored multiple times between m88 and m119. Upgrading to Avalonia 12.x would move to SkiaSharp 3.119.4 and likely fix this crash.

Note: SourceGit previously upgraded to Avalonia 12.0.4 (a0d51fee) but downgraded back to 11.3.18 (8477bdd0) due to TextEditor performance and memory issues.

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Questions

1. Has the TextEditor performance/memory issue that caused the downgrade from Avalonia 12.0.4 been resolved in Avalonia 12.1.0? Upgrading to 12.x would likely fix this crash as a side effect.
2. Is there a cleaner official way to pre-warm the font cache during startup (e.g., in BuildAvaloniaApp())?

[love-linger]

另外 Locale 沒有對應語言時 UI 會沒顯示任何文字，是否 fallback 到 en_US 會比較好

非常抱歉。我没有明白你的意思。能否举例说明复现步骤呢？目前所有提供的翻译都指定了 Fallback 到 en_US

Has the TextEditor performance/memory issue that caused the downgrade from Avalonia 12.0.4 been resolved in Avalonia 12.1.0?

Yes. But the performance/memory issue may not only due to TextEditor.

Is there a cleaner official way to pre-warm the font cache during startup (e.g., in BuildAvaloniaApp())?

I do not know.

[JC-Chung]

非常抱歉。我没有明白你的意思。能否举例说明复现步骤呢？目前所有提供的翻译都指定了 Fallback 到 en_US

手動編輯 preference.json 時的情況，如開頭提到的程式崩潰，只能透過手動修改為其他語言(ex. en_US)來開啟程式

以下則為 Locale 為空或不屬於任何語言時的截圖

[love-linger]

我并不打算支持或兼容手动填入非法值的情况。正如我在其他issue中回答的那样，preferences.json 仅是程序保存配置的文件，不建议用户手动编辑。