[vim/vim] Regular expression no longer matching when used in a syntax command (Issue #14908)

adrianconstantin-leroy

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Jun 3, 2024, 7:50:14 PM6/3/24

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Steps to reproduce

Open new Vim window and paste this (a pdoc (php) man page header):

ARRAY(3)                                                   1                                                   ARRAY(3)

array - Create an array

SYNOPSIS
       array array ([mixed  $...])

DESCRIPTION
        Creates an array. Read the section on the array type for more information on what an array is.

PARAMETERS
              o $...
                -  Syntax  "index => values", separated by commas, define index and values. index may be of type string

Search for the following pattern, that matches the first non-empty lines in the synopsis header

:set hls
/\v^SYNOPSIS\r?\n\zs.*\ze\r?\n\r?\n

Notice how the first line of the synopsis header gets highlighted.

Now use the same regular expression in a :syntax match command:

:set nohls
:syntax clear
:syntax match pdocSynopsisHeader /\v^SYNOPSIS\r?\n\zs.*\ze\r?\n\r?\n/
:highlight link pdocSynopsisHeader Special

Notice how the syntax does not change, and there is no match for the :syntax match command, despite the same regular expression is used as before.

You can double-check by moving the input cursor to the line in question (line 6) and calling synstack() function:

6G
:echo synstack(line('.'), col('.'))->map( { _, val -> synIDattr(val, "name") })
:syntax list pdocSynopsisHeader

What am I missing ? Some multi-line flag for the regexp ... ?

Expected behaviour

The regexp should match the same way in when used for a search (with / ) or when used in the :syntax command.
Or otherwise any differences should be documented as such.

Version of Vim

9.1 (patches 1-445)

Environment

Windows 10 GUI (gvim.exe)

Logs and stack traces

No response

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Christian Brabandt

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Jun 4, 2024, 2:50:53 AM6/4/24

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This seems more like a usage question and not necessarily a bug (at least not yet).

I see several issues here:

first of all, your use of \r?\n is not required, you can always use \n to match a linebreak, independently of what the fileformat option is set.
I seem to remember some issues with \zs and zero-width matches for syntax matches (not sure if this is documented). The following change works however: syn match Special /$^SYNOPSIS\n$\@<=.*$/. I think the difference is where the syntax engine is trying to start the match.
finally, I think using multi-line patterns as a :syn-match is not necessarily best-practice for syntax scripts. Better it is to define a region start and end patterns and then explicitly try to match within that region. So try this one instead (which is also more simpler to read:

syn region SYNOPSIS start="^SYNOPSIS" end="^$" contains=phpDescription
syn match phpDescription /^\s\+.*$/ contained
hi def link phpDescription Special

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Christian Brabandt

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Jun 4, 2024, 2:50:59 AM6/4/24

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@chrisbra converted this issue into discussion #14909.

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