* lisp/progmodes/grep.el (grep-num-matches-found): New variable.

(grep-mode-line-matches): New defconst.
(grep-mode-font-lock-keywords): Update the regexp for “Grep finished”
to include the number of matches found.
(grep-process-setup): Set grep-num-matches-found to 0.
(grep-exit-message): New function with body moved from lambda
in grep-process-setup.  Use grep-num-matches-found to return
the number of matches found.
(grep-filter): Increment grep-num-matches-found.
(grep-mode): Set compilation-mode-line-errors to grep-mode-line-matches.
(Bug#30397, bug#14017)

lisp/progmodes/grep.el

@@ -425,6 +425,14 @@ See `compilation-error-regexp-alist' for format details.")
 (defvar grep-context-face 'shadow
   "Face name to use for grep context lines.")
 
+(defvar grep-num-matches-found 0)
+
+(defconst grep-mode-line-matches
+  `(" [" (:propertize (:eval (int-to-string grep-num-matches-found))
+                      face ,grep-hit-face
+                      help-echo "Number of matches so far")
+    "]"))
+
 (defvar grep-mode-font-lock-keywords
    '(;; Command output lines.
      (": \\(.+\\): \\(?:Permission denied\\|No such \\(?:file or directory\\|device or address\\)\\)$"
@@ -432,7 +440,7 @@ See `compilation-error-regexp-alist' for format details.")
      ;; remove match from grep-regexp-alist before fontifying
      ("^Grep[/a-zA-z]* started.*"
       (0 '(face nil compilation-message nil help-echo nil mouse-face nil) t))
-     ("^Grep[/a-zA-z]* finished \\(?:(\\(matches found\\))\\|with \\(no matches found\\)\\).*"
+     ("^Grep[/a-zA-z]* finished with \\(?:\\(\\(?:[0-9]+ \\)?matches found\\)\\|\\(no matches found\\)\\).*"
       (0 '(face nil compilation-message nil help-echo nil mouse-face nil) t)
       (1 compilation-info-face nil t)
       (2 compilation-warning-face nil t))
@@ -503,21 +511,28 @@ Set up `compilation-exit-message-function' and run `grep-setup-hook'."
     (setenv "GREP_COLOR" "01;31")
     ;; GREP_COLORS is used in GNU grep 2.5.2 and later versions
     (setenv "GREP_COLORS" "mt=01;31:fn=:ln=:bn=:se=:sl=:cx=:ne"))
+  (setq-local grep-num-matches-found 0)
   (set (make-local-variable 'compilation-exit-message-function)
-       (lambda (status code msg)
-	 (if (eq status 'exit)
-	     ;; This relies on the fact that `compilation-start'
-	     ;; sets buffer-modified to nil before running the command,
-	     ;; so the buffer is still unmodified if there is no output.
-	     (cond ((and (zerop code) (buffer-modified-p))
-		    '("finished (matches found)\n" . "matched"))
-		   ((not (buffer-modified-p))
-		    '("finished with no matches found\n" . "no match"))
-		   (t
-		    (cons msg code)))
-	   (cons msg code))))
+       'grep-exit-message)
   (run-hooks 'grep-setup-hook))
 
+(defun grep-exit-message (status code msg)
+  "Return a status message for grep results."
+  (if (eq status 'exit)
+      ;; This relies on the fact that `compilation-start'
+      ;; sets buffer-modified to nil before running the command,
+      ;; so the buffer is still unmodified if there is no output.
+      (cond ((and (zerop code) (buffer-modified-p))
+	     (if (> grep-num-matches-found 0)
+                 (cons (format "finished with %d matches found\n" grep-num-matches-found)
+                       "matched")
+               '("finished with matches found\n" . "matched")))
+	    ((not (buffer-modified-p))
+	     '("finished with no matches found\n" . "no match"))
+	    (t
+	     (cons msg code)))
+    (cons msg code)))
+
 (defun grep-filter ()
   "Handle match highlighting escape sequences inserted by the grep process.
 This function is called from `compilation-filter-hook'."
@@ -535,7 +550,8 @@ This function is called from `compilation-filter-hook'."
         (while (re-search-forward "\033\\[0?1;31m\\(.*?\\)\033\\[[0-9]*m" end 1)
           (replace-match (propertize (match-string 1)
                                      'face nil 'font-lock-face grep-match-face)
-                         t t))
+                         t t)
+          (cl-incf grep-num-matches-found))
         ;; Delete all remaining escape sequences
         (goto-char beg)
         (while (re-search-forward "\033\\[[0-9;]*[mK]" end 1)
@@ -775,6 +791,8 @@ This function is called from `compilation-filter-hook'."
        grep-hit-face)
   (set (make-local-variable 'compilation-error-regexp-alist)
        grep-regexp-alist)
+  (set (make-local-variable 'compilation-mode-line-errors)
+       grep-mode-line-matches)
   ;; compilation-directory-matcher can't be nil, so we set it to a regexp that
   ;; can never match.
   (set (make-local-variable 'compilation-directory-matcher) '("\\`a\\`"))