Make compilation-mode regexp matching case-sensitive (bug#40119)

The number of regexps is large, they are written independently of one
another, and they frequently intersect.  Using case-sensitive matching
improves separation and performance, and is probably what everyone
have being assuming was used by compilation-mode all along.

* lisp/progmodes/compile.el (compilation-error-case-fold-search): New.
(compilation-parse-errors): Bind case-fold-search to
compilation-error-case-fold-search during matching.
* etc/NEWS: Announce.

2 files changed, 16 insertions, 1 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 1be5ad6acc0..910d9fa2d23 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -196,6 +196,12 @@ key             binding
 *** New user option 'gravatar-service' for host to query for gravatars.
 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.
+
 
 * New Modes and Packages in Emacs 28.1
 
diff --git a/lisp/progmodes/compile.el b/lisp/progmodes/compile.el
index 455f181f501..f4532b7edb7 100644
--- a/lisp/progmodes/compile.el
+++ b/lisp/progmodes/compile.el
@@ -646,6 +646,14 @@ 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
+  "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")
+
 ;;;###autoload(put 'compilation-directory 'safe-local-variable 'stringp)
 (defvar compilation-directory nil
   "Directory to restore to when doing `recompile'.")
@@ -1435,7 +1443,8 @@ to `compilation-error-regexp-alist' if RULES is nil."
     (if (symbolp item)
         (setq item (cdr (assq item
                               compilation-error-regexp-alist-alist))))
-    (let ((file (nth 1 item))
+    (let ((case-fold-search compilation-error-case-fold-search)
+          (file (nth 1 item))
           (line (nth 2 item))
           (col (nth 3 item))
           (type (nth 4 item))