fix(pattern): honour ^ anchor in gsub and literal caret in gmatch - #1
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Pattern.compile/1 returns an {anchored, elements} tuple, but only find/3
used the flag - gsub/4, gsub_stateful/5, and gmatch/2 discarded it.
Because compile strips the leading ^, those entry points matched the
remaining pattern at every position, so string.gsub("xax", "^x", "Y")
returned "YaY", 2 instead of "Yax", 1, silently corrupting the common
leading-trim idiom s:gsub("^%s+", "").
Route gsub and gsub_stateful through an anchored branch that tries the
match only at position 0 and replaces at most once, mirroring PUC-Lua
str_gsub's anchor flag. An n of 0 still suppresses the replacement, and
an empty anchored match (e.g. ^a* on "bbb") replaces once at the start.
gmatch needed the opposite treatment: per Lua 5.3 (and PUC-Lua's
gmatch_aux, which never strips the caret), a leading ^ in gmatch is not
an anchor but an ordinary literal character - so recompile the pattern
keeping the caret literal instead of dropping it.
Expected values in the regression tests are verified against PUC-Lua
5.3.6.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01F3LBtzmXgAMHA8QiGPa5Ek
fedme
approved these changes
Jul 27, 2026
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Mirror of tv-labs#406.
Pattern.compile/1 returns an {anchored, elements} tuple, but only find/3 used the flag - gsub/4, gsub_stateful/5, and gmatch/2 discarded it. This routes gsub/gsub_stateful through an anchored branch and keeps a leading
^literal in gmatch, matching PUC-Lua 5.3.6 semantics.Upstream PR: tv-labs#406