master d858a63: More robust auto-detect of grep-highlight-matches (bug#49978)

[Mattias Engdegård]

branch: master
commit d858a637c2ef35079fbc6cd8b2674c6b13de1e99
Author: Mattias Engdegård <mattiase@acm.org>
Commit: Mattias Engdegård <mattiase@acm.org>

    More robust auto-detect of grep-highlight-matches (bug#49978)
    
    * lisp/progmodes/grep.el (grep-compute-defaults):
    Don't require "grep --help" to finish with exit status 0 (BSD grep
    does not) and check the output in a slightly more robust way.
---
 lisp/progmodes/grep.el | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/lisp/progmodes/grep.el b/lisp/progmodes/grep.el
index 8f0a5ac..b2a9b3e 100644
--- a/lisp/progmodes/grep.el
+++ b/lisp/progmodes/grep.el
@@ -696,11 +696,12 @@ The value depends on `grep-command', `grep-template',
     (when (eq grep-highlight-matches 'auto-detect)
       (setq grep-highlight-matches
            (with-temp-buffer
-             (and (grep-probe grep-program '(nil t nil "--help"))
-                  (progn
-                    (goto-char (point-min))
-                    (search-forward "--color" nil t))
-                  ;; Windows and DOS pipes fail `isatty' detection in Grep.
+              ;; The "grep --help" exit status varies; pay no attention to it.
+              (grep-probe grep-program '(nil t nil "--help"))
+             (goto-char (point-min))
+             (and (let ((case-fold-search nil))
+                     (re-search-forward (rx "--color" (not (in "a-z"))) nil t))
+                  ;; Windows and DOS pipes fail `isatty' detection in Grep.
                   (if (memq system-type '(windows-nt ms-dos))
                       'always 'auto)))))