bug#54177: 28.0.91; project-find-regexp misbehaves with ripgrep over tramp/sudo

[Dmitry Gutov]

It shows only one match per file, apparently because the process
invocations over the 'sudo' transport are recognized as working in a
terminal. At least by ripgrep.

To repro:

1. (setq xref-search-program 'ripgrep)
2. C-x C-f /sudo:dgutov@localhost:vc/emacs/ RET
3. M-x project-find-regexp RET associative RET
4. Note seeing only one match per file.

FWIW, the fix is really simple:

diff --git a/lisp/progmodes/xref.el b/lisp/progmodes/xref.el
index 0ee7dd5cad..2fd5e19237 100644
--- a/lisp/progmodes/xref.el
+++ b/lisp/progmodes/xref.el
@@ -1626,7 +1626,7 @@ xref-search-program-alist
     (ripgrep
      .
      ;; '!*/' is there to filter out dirs (e.g. submodules).
-     "xargs -0 rg <C> --null -nH --no-messages -g '!*/' -e <R>"
+     "xargs -0 rg <C> --null -nH --no-heading --no-messages -g '!*/' -e 
<R>"
      ))
   "Associative list mapping program identifiers to command templates.

Is this okay for Emacs 28?

The problem might affect other Tramp transports as well (for all I
know), or maybe even other platforms. The risk for the fix seems minimal.