Re: [PROPOSAL] .gitignore syntax modification

[Nguyen Thai Ngoc Duy <pclouds@gmail.com>]

On Fri, Oct 15, 2010 at 6:01 PM, Kevin Ballard <kevin@sb.org> wrote:
> Got around to glancing at your patch. Looks pretty good, and it does build if you simply define EXC_FLAG_STARSTAR, though there are a few changes that are definitely necessary (a path of "*" will cause this to run off the end of the string while trying to detect "**/"). I'll have some more time next week to take a much closer look though. As for performance, I'm not particularly worried. The only performance change is if EXC_FLAG_STARSTAR is checked, in the worst-case it'll try to apply the pattern once per level of directory nesting. As this is just string twiddling, it's bound to be pretty fast, and I don't think there's any viable alternative to doing this kind of loop anyway. That said, I'd still like to support putting **/ anywhere in the pattern instead of just at the beginning, an
 d possibly even support ** (without the trailing /).

Well that would mean reimplementing fnmatch(). I don't know, maybe
it's not hard to do that. '*' can already match '/' if FNM_PATHNAME is
not given. So one just needs to tell fnmatch() '**' is '*' without
FNM_PATHNAME.

"**/" optimization can be extended to support "path/to/**/" quite
easily as long as no wildcards are used in "path/to/" part.

> If we do support ** by itself, I wonder if we should special-case having ** as the last path component of the pattern. The possible behavior change we could have is making this only match files and not directories. The use-case here is putting something like "foo/**" in the top-level .gitignore and then a few levels into foo we could put another .gitignore with an inverse pattern in order to un-ignore some deep file (or just "!foo/*/*/bar.c" inside that top-level .gitignore as well). The only way I can think of to achieve this behavior with the current gitignore is something along the lines of
>
> foo/*
> !foo/bar/
> foo/bar/*
> !foo/bar/baz/
> foo/bar/baz/*
> !foo/bar/baz/bar.c
>
> And even this will only work if you know all the intermediate directories. I cannot think of any way at all right now to ignore everything in a single directory except for one file at least 1 level of nesting deeper if you don't know the names of the intermediate directories. With the proposed special-case we can say
>
> foo/**
> !foo/*/*/bar.c
>
> and it will behave exactly as specified.
>
> It occurs to me that we could actually tweak this slightly, to say that if a ** is encountered and there are zero slashes in the pattern after it, then it will only match files (with zero or more leading directories). This way you can have a pattern "foo/**.d" which only ignores files with the extension ".d" but will still avoid ignoring directories that end in ".d".

No idea. Seems overkill to me. But I don't use .gitignore heavily. For
really complex ignore rules, how about allowing an external process to
do the job? It would keep .gitignore syntax simple, yet powerful when
needed.

A leading '|' marks an external process and can be used intermixed
with normal patterns in .gitignore. When excluded_from_list examines a
'|' pattern, it sends all information to the associated process' stdin
and expects to a result code in stdout. The process is started when it
is examined the first time and is kept alive until git process
terminates.
-- 
Duy