Fix font fallback crashing lualatex on recent TeX Live#14560
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On recent TeX Live (luaotfload v3.29), setting a font fallback (mainfontfallback/monofontfallback/...) crashes LuaLaTeX before a PDF is produced: luaotfload's fallback resolver dereferences a nil font. Quarto only showed a generic "compilation failed" with no usable signal, because the crash is a Lua runtime error with no standard "! ...Here is how much" block for the log parser to key off. Detect the crash signature in findLatexError and return a message that names the fallback options, explains it is a known upstream luaotfload bug on this TeX Live, and points to the single-font workaround. Upstream report: latex3/luaotfload#331 See #14553.
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luaotfload appends a ";-fallback" feature to every font name passed to
add_fallback() (to disable recursion). Its request grammar only ends a
font name at ":", "(" or "/", so a bare name like "DejaVu Sans" absorbs
the appended ";-fallback" into the name itself: the lookup fails,
define_font returns nil, and LuaLaTeX crashes dereferencing it
(luaotfload-fallback.lua: attempt to index a nil value). Terminating
each fallback name with ":" lets the appended feature parse as a feature
rather than part of the name, so the fallback resolves and the document
compiles.
This is what made mainfontfallback/sansfontfallback/monofontfallback
crash rather than fill in missing glyphs on recent TeX Live.
See latex3/luaotfload#331
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When a document sets a font fallback (
mainfontfallback,monofontfallback, ...) and renders to PDF with lualatex on recent TeX Live (luaotfload v3.29), lualatex crashes before producing a PDF and Quarto reports only a genericcompilation failed- error.Root Cause
luaotfload appends an internal
;-fallbackfeature to each fallback name and resolves it withdefine_font. Its font-name parser ends a name only at:,(or/, so a bare name like"DejaVu Sans"absorbs the appended feature (DejaVu Sans;-fallback), the lookup fails,define_fontreturnsnil, andluaotfload-fallback.luathen dereferences thenil. The template insrc/resources/formats/pdf/pandoc/font-settings.latexemitted fallback names without a trailing colon.Because the crash is a Lua runtime error with no
! ...Here is how muchblock,findLatexErrorinsrc/command/render/latexmk/parse-error.tsextracted nothing, leaving the user with a generic failure and no signal.Fix
Emit each fallback name colon-terminated (
"DejaVu Sans:") so the appended;-fallbackparses as a feature rather than part of the name. The fallback then resolves and the document compiles. A luaotfload maintainer confirmed the colon form as correct in latex3/luaotfload#331.The crash-detection diagnostic in
parse-error.tsis kept as a safety net: if a fallback crash is still detected (e.g. a hand-written raw-LaTeX fallback),findLatexErrorreturns an actionable message instead of a generic failure.Pandoc's template emits colon-less names the same way; reported upstream at jgm/pandoc#11678.
Test Plan
monofont+ multiplemonofontfallbackentries on lualatex (TeX Live 2026) — compiles with fallbacks active, no crashtests/docs/smoke-all/2026/06/01/14553.qmdverifies the generated LaTeX emits colon-terminated fallback names and compilestests/unit/latexmk/parse-error.test.tscovers the crash-log signature for the diagnostic safety netFixes #14553