fix(powerline): fall back to a plain | separator when no Powerline font is detected - #13
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…nt is detected Powerline/Nerd Font glyphs (private-use area) render as mojibake when the terminal has no matching font; checkPowerlineFonts() could detect this, but only the TUI setup flow surfaced it. Now every powerline separator, cap, and user-typed separator character is checked at render time: PUA glyphs degrade to '|' when no font is detected and pass through untouched otherwise. Detection is a directory scan, cached for the process lifetime; installing fonts through the TUI resets the cache. Tests can pin the detection via setCachedPowerlineFontStatus() so renders stay deterministic regardless of the machine's fonts. Closes the bug half of sirmalloc#604. Co-Authored-By: Claude Code <noreply@anthropic.com>
This was referenced Sep 27, 2026
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Closes the bug half of sirmalloc#604 (the feature half is handled by sirmalloc#607).
Problem
The default powerline separator is the private-use-area glyph U+E0B0. Without a Powerline/Nerd Font it renders as mojibake, and while
checkPowerlineFonts()can detect the absence of fonts, that warning only surfaced in the TUI setup flow — enabling powerline via config/CLI on a machine without fonts produced garbage glyphs in every render with no hint of the cause. Regular-mode separators suffer the same when users type PUA characters as their separator.Fix
Render-time font-safe pass, applied to:
separators,startCaps,endCaps(renderer's powerline path);characteranddefaultSeparator(renderer's regular path).Mechanics:
fontSafeSeparator(): text containing a PUA glyph (BMP PUAU+E000–F8FFplus the astral Nerd Font planes) degrades to'|'when the detection reports no font; everything else passes through untouched, and glyphs are kept when a font is detected.checkPowerlineFonts(), a directory scan) is cached for the process lifetime so renders stay cheap;installPowerlineFonts()resets the cache so newly installed fonts stop the fallback.setCachedPowerlineFontStatus()is a small test seam: tests pin the detection result, so renderer output is deterministic regardless of the machine's fonts (several existing glyph-asserting tests now seedinstalled: true).Known limitation
Detection is disk-based (font directories + name patterns) — it cannot know which font the terminal actually uses. A machine with a Nerd Font installed on disk but a non-Nerd font selected in the terminal will keep the glyphs (and the mojibake). Surfacing a hint in that case would need a config knob or TUI message; left out to keep this change small.
Verification
separator-font-fallback.test.ts: glyph detection (BMP + astral), fallback with fonts absent, pass-through with fonts present, and full renders in powerline mode and regular mode (PUA separator character) asserting|and noU+E0B0.renderer-dim,renderer-flex-width) pinned via the test seam — all green.bun testfull suite: only the pre-existing timing-flaky subprocess tests flicker (pass in isolation);bun run lintclean;bun run buildOK.U+E0B0separators rendered through the built binary on a font-less machine emits|and zero mojibake bytes.🤖 Generated with Claude Code