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vim-patch:e9c5e56: runtime(python): improve performance of number and ellipsis matching (#41608)

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Problem:  The floating-point `.d` number match and the two ellipsis
          matches are slow: each begins with a look-behind, which cannot
          be reduced to a fixed first character, so the automatic regexp
          engine selects the slower NFA backend for them.
Solution: Force the backtracking engine with \%#=1 on those three
          patterns; it evaluates the look-behind far more efficiently.
          Highlighting is unchanged.

Measured with :syntime over a 40000 line corpus: the three affected
rules drop from ~0.13s to ~0.008s (about -93%), which cuts the total
syntax parse cost by ~10% (1.85s to 1.65s).

closes: vim/vim#21194

e9c5e56081

Co-authored-by: Julien Voisin <julien.voisin@dustri.org>
This commit is contained in:
zeertzjq
2026-09-02 13:51:57 +08:00
committed by GitHub
parent d42367570c
commit 8e34903b6a
1 changed files with 7 additions and 4 deletions
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11
runtime/syntax/python.vim
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@@ -7,6 +7,7 @@
" 2026 Jan 26 by Vim Project: highlight constants #18922
" 2026 Mar 11 by Vim Project: fix number performance #19630
" 2026 May 27 by Vim Project: highlight `lazy` soft keyword (PEP 810) #20342
" 2026 Aug 30 by Vim Project: improve number and ellipsis performance
" Credits: Neil Schemenauer <nas@python.ca>
" Dmitry Vasiliev
" Rob B
@@ -285,9 +286,9 @@ if !exists("python_no_number_highlight")
" \d\.\d
syn match pythonNumber
\ "\<\d\+\%(_\d\+\)*\.\d\+\%(_\d\+\)*\%([eE][+-]\=\d\+\%(_\d\+\)*\)\=[jJ]\=\>"
" \.\d
" \.\d -- \%#=1 selects the faster backtracking engine (leading look-behind)
syn match pythonNumber
\ "\%(^\|\W\)\@1<=\.\d\+\%(_\d\+\)*\%([eE][+-]\=\d\+\%(_\d\+\)*\)\=[jJ]\=\>"
\ "\%#=1\%(^\|\W\)\@1<=\.\d\+\%(_\d\+\)*\%([eE][+-]\=\d\+\%(_\d\+\)*\)\=[jJ]\=\>"
endif
" Group the built-ins in the order in the 'Python Library Reference' for
@@ -330,7 +331,8 @@ if !exists("python_no_builtin_highlight")
\ contains=ALLBUT,pythonBuiltin,pythonClass,pythonFunction,pythonType,pythonAsync
\ transparent
" the ellipsis literal `...` can be used in multiple syntactic contexts
syn match pythonEllipsis "\.\@1<!\.\.\.\ze\.\@!" display
" \%#=1 selects the faster backtracking engine (leading look-behind)
syn match pythonEllipsis "\%#=1\.\@1<!\.\.\.\ze\.\@!" display
endif
" From the 'Python Library Reference' class hierarchy at the bottom.
@@ -390,7 +392,8 @@ if !exists("python_no_doctest_highlight")
syn region pythonDoctestValue
\ start=+^\s*\%(>>>\s\|\.\.\.\s\|"""\|'''\)\@!\S\++ end="$"
\ contained contains=pythonEllipsis
syn match pythonEllipsis "\%(^\s*\)\@<!\.\@1<!\zs\.\.\.\ze\.\@!" display
" \%#=1 selects the faster backtracking engine (leading look-behind)
syn match pythonEllipsis "\%#=1\%(^\s*\)\@<!\.\@1<!\zs\.\.\.\ze\.\@!" display
\ contained containedin=pythonDoctest
else
syn region pythonDoctest