bug#33618: better fix

[Stephen Leake <stephen_leake@stephe-leake.org>]

`grep-mode' is defined by `define-compilation-mode', which sets
`compilation-search-path' to a buffer-local copy of `grep-search-path',
if the latter is defined.

So there is precedent for making custom vars buffer-local, and it seems
the proper fix for this bug is to define `grep-search-path':

--- a/lisp/progmodes/grep.el
+++ b/lisp/progmodes/grep.el
@@ -441,6 +441,14 @@ grep-find-abbreviate
   :version "27.1"
   :group 'grep)
 
+(defcustom grep-search-path '(nil)
+  "Search path for grep results.
+Elements should be directory names, not file names of directories.
+The value nil as an element means to try the default directory."
+  :group 'grep
+  :type '(repeat (choice (const :tag "Default" nil)
+			 (string :tag "Directory"))))
+
 (defvar grep-find-abbreviate-properties
   (let ((ellipsis (if (char-displayable-p ?…) "[…]" "[...]"))
         (map (make-sparse-keymap)))


`emacs-lisp-compilation-mode' needs a similar fix:

--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -1022,6 +1022,14 @@ emacs-lisp-compilation-parse-errors-filename-function
   "The value for `compilation-parse-errors-filename-function' for when
 we go into emacs-lisp-compilation-mode.")
 
+(defcustom emacs-lisp-compilation-search-path '(nil)
+  "Search path for byte-compile error messages.
+Elements should be directory names, not file names of directories.
+The value nil as an element means to try the default directory."
+  :group 'bytecomp
+  :type '(repeat (choice (const :tag "Default" nil)
+			 (string :tag "Directory"))))
+
 (define-compilation-mode emacs-lisp-compilation-mode "elisp-compile"
   "The variant of `compilation-mode' used for emacs-lisp error buffers")

-- 
-- Stephe