bug#49836: Support ripgrep in semantic-symref-tool-grep

[Juri Linkov <juri@linkov.net>]

>>> I think the original idea (surrounding with \W) is sound: after all, not
>>> every symbol boundary in Emacs sense is a word boundary in Grep or RG. If
>>> a method, say, ends with ?, then it won't be.
>> I tried to search for 'soap-type-is-array?' in the Emacs tree,
>> and ripgrep can find it with "\\b%s\\b", but Grep can't.
>
> Did you search through symref, or in console? If the former, it seems some
> regexp-quoting is missing somewhere (the question mark was no
> escaped). Because see what the console says:
>
> $ rg "\bsoap-type-is-array?\b"
> lisp/net/soap-client.el
> 950:(defun soap-type-is-array? (type)
> 990:                       (if (soap-type-is-array? type)
>
> ChangeLog.2
> 19080:	* lisp/net/soap-client.el (soap-type-is-array?): new defun
>
> $ rg "\bsoap-type-is-array\?\b"
>
> ^^ no matches
>
> And
>
> $ rg "\bsoap-type-is-array\?"
>
> has matches, of course.

semantic-symref-grep-use-template constructs such command line:

  "rg ... -e \\\\bsoap-type-is-array\\?\\\\b"

that finds matches.

>> It would be more preferable not to change the existing default logic
>> to avoid possible troubles.  Since Grep with Basic syntax works fine,
>> then better not to switch to Extended syntax.
>
> See above. But also consider what happens if a user sees that grep-program
> is now customizable and ripgrep is an officially supported value. They
> change it to "rg", and then suddenly their 'M-x rgrep' input has to use the
> extended regexp format?

This difference could be explained in the documentation.

> Worse than that, any third-party package that uses grep-find-template will
> suddenly have a high chance of failing if they pass any nontrivial regexps
> to it, especially if those have groupings or alternations.

This already happened after trying to customize grep-find-template
to use rg broke xref-find-references, so the problem already exists
and needs to be solved.

> It's a hard problem: grep.el is not prepared for abstracting like that. If
> we at least standardized it internally on Extended format, that would at
> least remove one source of uncertainty and bugs. The user still can input
> basic regexps interactively, we can translate them easily.

Is there a package that can translate between them reliably?

> Further: seeing xref-search-program-alist, people asked for support for
> other similar programs, such as ag and pt. Any solution we end up with, we
> should try to ensure they are valid values of grep-program as well.

Why not, semantic-symref already supports alternative tools
such as cscope, global, idutils.  So xref could support more too.

>> +                         (if (equal grep-program "rg")
>> +                             (format "(^|\\W)%s(\\W|$)"
>> +                                     (oref tool searchfor))
>> +                           (format "\\(^\\|\\W\\)%s\\(\\W\\|$\\)"
>> +                                   (oref tool searchfor))))))
>
> This can work. Except the comparison should be with "grep", I think: all
> other alternatives only work with the Extended format.

I'm worried about the case when the user customizes
'grep-program' to e.g. an absolute path "/bin/grep"
or "/usr/local/bin/grep", etc.