matchparen.vim incorrectly assumes hl id 3 is available

[justinmk]

Sometimes when moving quickly through some code after saving or swapping buffers, this error occurs:

Error detected while processing function <SNR>29_Highlight_Matching_Pair: 
line  140: 
E801: ID already taken: 3

In runtime/plugin/matchparen.vim, s:Highlight_Matching_Pair() calls matchdelete(3) at the start of that function but that is skipped under certain conditions.

Some other plugin may call matachadd(..., 3) or :3match, and then matchparen.vim tries to use that hl id anyway.

This could be fixed by storing the next available hl id in w:paren_hl_on instead of always using 3, then matchdelete(w:paren_hl_on).

[jamessan]

@benjifisher should be notified about this. I notice there is a repo on GitHub for matchit.

[k-takata]

@jamessan
It is matchit, not matchparen.

[chrisbra]

Actually, the current behaviour is documented. It strongly discourages the use of id 3
:h matchadd()

            ...
            message will appear and the match will not be added.  An ID
            is specified as a positive integer (zero excluded).  IDs 1, 2
            and 3 are reserved for :match, :2match and :3match,
            respectively.  

and then later at :h 3match

            Just like :match above, but set a separate match.  Thus
            there can be three matches active at the same time.  The match
            with the lowest number has priority if several match at the
            same position.
            The ":3match" command is used by the matchparen plugin.  You
            are suggested to use ":match" for manual matching and
            ":2match" for another plugin.

(just pointing out the obvious, I am not against changing matchparen and taking the next free id.)

[brammool]

Right, id 3 is reserved for matchparen, always has been.
Can you find out what the offending plugin is?

[chrisbra]

closing. This was an issue with w0rp/ale plugin which has been fixed since then.