Turn compilation-error-case-fold-search into a defvar

See bug#40119, and the discussion at
https://lists.gnu.org/archive/html/emacs-devel/2020-03/msg00653.html

* lisp/progmodes/compile.el (compilation-error-case-fold-search):
Turn into a defvar.
* etc/NEWS: Update.

2 files changed, 10 insertions, 6 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 49b7fcd8c21..870d39f7eef 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -218,8 +218,10 @@ Defaults to 'libravatar', with 'unicornify' and 'gravatar' as options.
 ** Compilation mode
 
 *** Regexp matching of messages is now case-sensitive by default.
-The user option 'compilation-error-case-fold-search' can be set
-for case-insensitive matching of messages.
+The variable 'compilation-error-case-fold-search' can be set for
+case-insensitive matching of messages when the old behaviour is
+required, but the recommended solution is to use a correctly matching
+regexp instead.
 
 
 * New Modes and Packages in Emacs 28.1
diff --git a/lisp/progmodes/compile.el b/lisp/progmodes/compile.el
index f4532b7edb7..e5878b28f96 100644
--- a/lisp/progmodes/compile.el
+++ b/lisp/progmodes/compile.el
@@ -646,13 +646,15 @@ matched file names, and weeding out false positives."
   :link `(file-link :tag "example file"
                     ,(expand-file-name "compilation.txt" data-directory)))
 
-(defcustom compilation-error-case-fold-search nil
+(defvar compilation-error-case-fold-search nil
   "If non-nil, use case-insensitive matching of compilation errors
 by the regexps of `compilation-error-regexp-alist' and
 `compilation-error-regexp-alist-alist'.
-If nil, matching is case-sensitive."
-  :type 'boolean
-  :version "28.1")
+If nil, matching is case-sensitive.
+
+This variable should only be set for backward compatibility as a temporary
+measure.  The proper solution is to use a regexp that matches the
+messages without case-folding.")
 
 ;;;###autoload(put 'compilation-directory 'safe-local-variable 'stringp)
 (defvar compilation-directory nil