Vim syntax partial match

Question

I'm trying to match a new line character on a Vim syntax file, I can make it work when I use the patern within Vim but when I put it in my syntax file it doesn't highlight when I have a new line and when it should.

The regex part that I use for new line match is: \_s (also tried with \n with: \(\n\|\s\))

The patern: [,(]\(\_s*\w\+:\)\?\_s*\zs\w\+

Simplified version of the patern: [,(]\_s*\zs\w\+ (same for the example and the purpose of the question)

Syntax file code inside .vim/syntax/python.vim:

syn match pythonFunctionParam '[,(]\_s*\zs\w\+'
[...]
hi link pythonFunctionParam Error
[...]
let b:current_syntax = 'python'

Here is a sample test file to reproduce try: test.py :

a(matched_by_all=2, matched_by_all="anything")
b(  matched_by_all=3,
    matched_only_by_vim_search='test'
)
c(
    matched_only_by_vim_search=3
    matched_by_none="it's normal"
)

When I use Vim integrated search ( /[,(]\_s*\zs\w\+ ) I get thoses matches:

  matched_by_all    matched_by_all
    matched_by_all
    matched_only_by_vim_search


    matched_only_by_vim_search
    

So everything works has expected

When I use syntax syn match with the same regex I get different matches (less match):

  matched_by_all    matched_by_all
    matched_by_all

Has you can see when there is a ( or , on the same line it will match, but not if it's a new line.

So my question is: How to get the same match in my syntax file ?

Answer 1

Looks like vim syntax match regexp engine doesn't like \zs and \_s. If you remove \zs you can see matches:

I would go with another approach:

1. define transparent function call region that contains function parameters
2. define contained function paramenter

syn region pythonFunctionCall start='\k\+\_s*(\zs' end='\ze)' contains=pythonFunctionParam transparent keepend
syn match pythonFunctionParam '\k\+\(\s*=\s*[^,]\+\)\?' contained
hi link pythonFunctionParam Error

NOTE: pythonFunctionParam is just a simple example you can tune.

Answer 2

There is an explicit exception to how \zs works in a syntax match in that it must match on the same line as the pattern starts.

See :help syn-multi-line:

The patterns can include "\n" to match an end-of-line. Mostly this works as expected, but there are a few exceptions.

When using a start pattern with an offset, the start of the match is not allowed to start in a following line. The highlighting can start in a following line though. Using the \zs item also requires that the start of the match doesn't move to another line.

You can work around that by using a zero-width look-behind match instead:

syn match pythonFunctionParam '\([,(]\_s*\)\@<=\w\+'

But note that this kind of match tends to be more expensive. If you use one, try to limit its scope. The syntax engine in Vim also offers other mechanisms that can help you narrow down your matches, for example you can match certain groups only when they occur inside specific other groups, this might help implement this kind of syntax using simpler matches.