(makefile-dependency-regex): Fix bug#76759

* lisp/progmodes/make-mode.el (makefile-dependency-regex):
Decompose the regexp to be more understandable, and then change
it so the target part can't accidentally match a TAB.

* test/lisp/progmodes/make-mode-tests.el (make-mode-tests--bug17400):
New test.

lisp/progmodes/make-mode.el

@@ -225,8 +225,18 @@ not be enclosed in { } or ( )."
 ;; that if you change this regexp you might have to fix the imenu
 ;; index in makefile-imenu-generic-expression.
 (defvar makefile-dependency-regex
-  ;; Allow for two nested levels $(v1:$(v2:$(v3:a=b)=c)=d)
-  "^\\(\\(?:\\$\\(?:[({]\\(?:\\$\\(?:[({]\\(?:\\$\\(?:[^({]\\|.[^\n$#})]+?[})]\\)\\|[^\n$#)}]\\)+?[})]\\|[^({]\\)\\|[^\n$#)}]\\)+?[})]\\|[^({]\\)\\|[^\n$#:=]\\)+?\\)\\(:\\)\\(?:[ \t]*$\\|[^=\n]\\(?:[^#\n]*?;[ \t]*\\(.+\\)\\)?\\)"
+  (letrec ((elems-re
+            (lambda (n &optional outer)
+              (if (< n 1)
+                   "[^\n$#})]+?"
+                (concat "\\(?:\\$\\(?:"
+                        "[({]" (funcall elems-re (- n 1)) "[})]"
+                        "\\|[^({]\\)"
+                        "\\|[^\n$#" (if outer "\t:=" ")}") "]\\)+?")))))
+    (concat
+     ;; Allow for two nested levels $(v1:$(v2:$(v3:a=b)=c)=d)
+     "^\\(" (funcall elems-re 3 'outer)
+     "\\)\\(:\\)\\(?:[ \t]*$\\|[^=\n]\\(?:[^#\n]*?;[ \t]*\\(.+\\)\\)?\\)"))
   "Regex used to find dependency lines in a makefile.")
 
 (defconst makefile-bsdmake-dependency-regex

test/lisp/progmodes/make-mode-tests.el

@@ -0,0 +1,42 @@
+;;; make-mode-tests.el --- tests for make-mode.el   -*- lexical-binding: t -*-
+
+;; Copyright (C) 2025 Free Software Foundation, Inc.
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Code:
+
+(require 'ert)
+
+(ert-deftest make-mode-tests--bug17400 ()
+  (let ((code "
+foo:
+	bar; : baz"))
+    (with-temp-buffer
+      (insert code "\n")
+      (makefile-mode)
+      (font-lock-ensure)
+      (re-search-backward "bar")
+      (let ((bar-pos (point)))
+        (re-search-backward "foo")
+        (let ((foo-pos (point)))
+          ;; Make sure we don't confuse "bar;:" for a target!
+          (should-not (equal (get-text-property bar-pos 'face)
+                             (get-text-property foo-pos 'face))))))))
+
+(provide 'make-mode-tests)
+
+;;; make-mode-tests.el ends here