How best to set grep command based on current directory?

How best to set grep command based on current directory?

[Michael Welsh Duggan]

I would like to change the program invocation in "M-x grep" (or maybe
"M-x grep-find") to default to "git grep" when in directories that are
in git trees.  I could hack away at the grep.el sources to do this, or I
could write some advice around the grep command to do this, but I want
to ask here, first, if anyone believes that there is a more principled
way to make this change.

-- 
Michael Welsh Duggan
(md5i@md5i.com)

Re: How best to set grep command based on current directory?

[Eli Zaretskii]

> From: Michael Welsh Duggan <mwd@md5i.com>
> Date: Fri, 08 Apr 2022 21:10:19 -0400
> 
> I would like to change the program invocation in "M-x grep" (or maybe
> "M-x grep-find") to default to "git grep" when in directories that are
> in git trees.  I could hack away at the grep.el sources to do this, or I
> could write some advice around the grep command to do this, but I want
> to ask here, first, if anyone believes that there is a more principled
> way to make this change.

That must be an opt-in behavior, to avoid surprising the users.
"M-x grep" is a very old command, so I don't think we can change
its behavior in such radical ways unconditionally.

Re: How best to set grep command based on current directory?

[Yuri Khan]

On Sat, 9 Apr 2022 at 08:11, Michael Welsh Duggan <mwd@md5i.com> wrote:

> I would like to change the program invocation in "M-x grep" (or maybe
> "M-x grep-find") to default to "git grep" when in directories that are
> in git trees.  I could hack away at the grep.el sources to do this, or I
> could write some advice around the grep command to do this, but I want
> to ask here, first, if anyone believes that there is a more principled
> way to make this change.

I customize grep-command to "git --no-pager grep -nH -E -e ". When not
inside a git repository, or if I want to search untracked files, I
manually add --no-index.

Re: How best to set grep command based on current directory?

[Jim Porter]

On 4/8/2022 6:10 PM, Michael Welsh Duggan wrote:
> I would like to change the program invocation in "M-x grep" (or maybe
> "M-x grep-find") to default to "git grep" when in directories that are
> in git trees.  I could hack away at the grep.el sources to do this, or I
> could write some advice around the grep command to do this, but I want
> to ask here, first, if anyone believes that there is a more principled
> way to make this change.

If *recursive* grep is ok (as opposed to `M-x grep'), that's what I 
wrote urgrep[1] to do. It's aware of Git directories as well as remote 
Tramp hosts that may have a different set of commands available for use. 
I've seen using it for a while and I think I've worked out most of the 
bugs. (I haven't submitted it for inclusion in GNU ELPA yet since I'm 
still debating on what to do with a few parts, especially the API.)

If not, maybe the code will at least give you some ideas. After a fair 
bit of experimentation, I found that the following command produces the 
most consistent rgrep-like results for both Git and non-Git directories:

   git grep --no-index --exclude-standard

Even within Git repos, I found the above to work best, since it searches 
untracked files (excluding .gitignored files) and recurses into 
submodules. The fact that it also works well for non-Git directories is 
a nice bonus too.

- Jim

[1] https://github.com/jimporter/urgrep