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

[Dmitry Gutov <dgutov@yandex.ru>]

I think we can improve this part:

On 03.08.2021 11:10, Juri Linkov wrote:
> diff --git a/lisp/cedet/semantic/symref/grep.el b/lisp/cedet/semantic/symref/grep.el
> index 180d779a78..034f797076 100644
> --- a/lisp/cedet/semantic/symref/grep.el
> +++ b/lisp/cedet/semantic/symref/grep.el
> @@ -150,15 +150,14 @@ semantic-symref-perform-search
>                              "-l ")
>                             ((eq (oref tool searchtype) 'regexp)
>                              "-nE ")
> -                          (t "-n ")))
> +                          (t (if (equal grep-program "rg") "" "-n "))))

It might be cleaner to see whether grep-find-template already includes 
that flag, and if so, omit it. Though the search might be non-trivial if 
it's in the form like "-abcn", still, that's searchable by regexp.

>            (greppat (cond ((eq (oref tool searchtype) 'regexp)
>                            (oref tool searchfor))
>                           (t
>                            ;; Can't use the word boundaries: Grep
>                            ;; doesn't always agree with the language
>                            ;; syntax on those.
> -                         (format "\\(^\\|\\W\\)%s\\(\\W\\|$\\)"
> -                                 (oref tool searchfor)))))
> +                         (format "\\b%s\\b" (oref tool searchfor)))))
>   	 ;; Misc
>   	 (b (get-buffer-create "*Semantic SymRef*"))
>   	 (ans nil)

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.

The problem with the above regexp is that it uses the basic syntax, 
instead of Extended. But we can flip it.

As long as we're able to ask Grep to search with Extended syntax, we can 
use (format "(^|\\W)%s(\\W|$)" (oref tool searchfor)). And that can be 
achieved with the same method as is used in xref-matches-in-directory:

Something like (replace-regexp-in-string "grep <C>" "grep <C> -E" 
                                               grep-find-template t t), 
to be sure it's not ripgrep in there.

The new user option can be used too, but I'd probably prefer a more 
independent solution here.