From: Mattias Engdegård <mattiase@acm.org>
Date: Tue, 10 Aug 2021 15:04:34 +0000 (+0200)
Subject: More robust auto-detect of grep-highlight-matches (bug#49978)
X-Git-Tag: emacs-28.0.90~1567
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=d858a637c2ef35079fbc6cd8b2674c6b13de1e99;p=emacs.git

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.
---

diff --git a/lisp/progmodes/grep.el b/lisp/progmodes/grep.el
index 8f0a5acf708..b2a9b3e3206 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)))))