bug#36644: Git log search

[Juri Linkov]

It would be very useful to have the command to grep git logs,
for instance, to search commits by bug numbers in format "bug#36789"
and many other such use cases:

diff --git a/lisp/vc/vc.el b/lisp/vc/vc.el
index eb6d6d331f..d39af516a9 100644
--- a/lisp/vc/vc.el
+++ b/lisp/vc/vc.el
@@ -337,6 +337,10 @@
 ;;   Insert in BUFFER the revision log for the changes that will be
 ;;   received when performing a pull operation from REMOTE-LOCATION.
 ;;
+;; - log-search (pattern)
+;;
+;;   Search for PATTERN in the revision log.
+;;
 ;; - log-view-mode ()
 ;;
 ;;   Mode to use for the output of print-log.  This defaults to
@@ -2526,6 +2530,16 @@ vc-log-outgoing
     (vc-incoming-outgoing-internal backend (or remote-location "")
                                    "*vc-outgoing*" 'log-outgoing)))
 
+;;;###autoload
+(defun vc-log-search (pattern)
+  "Search a log of changes for PATTERN."
+  (interactive (list (read-regexp "Log search pattern: ")))
+  (let ((backend (vc-deduce-backend)))
+    (unless backend
+      (error "Buffer is not version controlled"))
+    (vc-incoming-outgoing-internal backend pattern
+                                   "*vc-search*" 'log-search)))
+
 ;;;###autoload
 (defun vc-log-mergebase (_files rev1 rev2)
   "Show a log of changes between the merge base of REV1 and REV2 revisions.
diff --git a/lisp/vc/vc-git.el b/lisp/vc/vc-git.el
index 8b82856332..d1d6a7408e 100644
--- a/lisp/vc/vc-git.el
+++ b/lisp/vc/vc-git.el
@@ -1073,6 +1075,13 @@ vc-git-log-incoming
                        "@{upstream}"
                      remote-location))))
 
+(defun vc-git-log-search (buffer pattern)
+  (vc-setup-buffer buffer)
+  (vc-git-command
+   buffer 'async nil
+   "log"
+   "--no-color" "-i" (format "--grep=%s" pattern)))
+
 (defun vc-git-mergebase (rev1 &optional rev2)
   (unless rev2 (setq rev2 "HEAD"))
   (string-trim-right (vc-git--run-command-string nil "merge-base" rev1 rev2)))
@@ -1089,7 +1100,7 @@ vc-git-log-view-mode
   (set (make-local-variable 'log-view-file-re) regexp-unmatchable)
   (set (make-local-variable 'log-view-per-file-logs) nil)
   (set (make-local-variable 'log-view-message-re)
-       (if (not (eq vc-log-view-type 'long))
+       (if (not (memq vc-log-view-type '(long log-search)))
           (cadr vc-git-root-log-format)
         "^commit *\\([0-9a-z]+\\)"))
   ;; Allow expanding short log entries.
@@ -1098,7 +1109,7 @@ vc-git-log-view-mode
     (set (make-local-variable 'log-view-expanded-log-entry-function)
         'vc-git-expanded-log-entry))
   (set (make-local-variable 'log-view-font-lock-keywords)
-       (if (not (eq vc-log-view-type 'long))
+       (if (not (memq vc-log-view-type '(long log-search)))
           (list (cons (nth 1 vc-git-root-log-format)
                       (nth 2 vc-git-root-log-format)))
         (append