bug#67062: 30.0.50; [PATCH] Abbreviate the revision in 'vc-annotate' (for Git)

[Jim Porter <jporterbugs@gmail.com>]

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On 11/11/2023 2:00 PM, Dmitry Gutov wrote:
> On 11/11/2023 09:41, Eli Zaretskii wrote:
>> If this is a Git-only issue, perhaps it would be better to have a
>> Git-only option, instead of defining a whole new VC method?
> 
> Our general approach is to prefer global options and dynamic dispatch on 
> backends, resorting to using per-backend options when it's much easier 
> to do.
> 
> In this case it might actually be more difficult to go the second route 
> since the intention is to only use the short hash in this particular 
> place. vc-annotate is common code and it will need to indicate that 
> intention to the backend somehow.

Thanks for taking a look. It sounds like the strategy I went with is at 
least approximately right, so here's an updated patch with a NEWS entry.

I looked through the manuals and didn't see anywhere to add a mention of 
this though. There's a section about 'vc-annotate', but it's written for 
an Emacs user, rather than an Elisp programmer, and I think trying to 
explain "short revisions" in that section would just add unnecessary 
detail. If we still want to add some mention of this to a manual, I 
guess it would make the most sense in some section about how to use the 
VC package as an Elisp programmer. I didn't see much about that though...

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From 3dd9434161b36f01397c3269ca839bca3db0d59e Mon Sep 17 00:00:00 2001
From: Jim Porter <jporterbugs@gmail.com>
Date: Fri, 10 Nov 2023 18:42:29 -0800
Subject: [PATCH] Abbreviate the VC revision in vc-annotate's buffer name

* lisp/vc/vc-annotate.el (vc-annotate): Call 'short-revision'

* lisp/vc/vc-hooks.el (vc-default-short-revision): New function.

* lisp/vc/vc-git.el (vc-git-short-revision): New function.
(vc-git--rev-parse): New optional argument SHORT.

* etc/NEWS: Announce this change (bug#67062).
---
 etc/NEWS               |  6 ++++++
 lisp/vc/vc-annotate.el |  4 +++-
 lisp/vc/vc-git.el      | 14 +++++++++++---
 lisp/vc/vc-hooks.el    |  5 +++++
 4 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/etc/NEWS b/etc/NEWS
index 767e4c27b43..0632001648c 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -396,6 +396,12 @@ switches for shortlogs, such as the one produced by 'C-x v L'.
 *** Obsolete command 'vc-switch-backend' re-added as 'vc-change-backend'.
 The command was previously obsoleted and unbound in Emacs 28.
 
+---
+*** 'vc-annotate' can now abbreviate the revision in the buffer name.
+VC backends with a 'vc-BACKEND-short-revision' functions can convert a
+revision to a shorter form, and 'vc-annotate' will use this form in
+its buffer name.  Currently, the Git backend supports this.
+
 ** Diff mode
 
 +++
diff --git a/lisp/vc/vc-annotate.el b/lisp/vc/vc-annotate.el
index de6c3adbbdb..85161347cbf 100644
--- a/lisp/vc/vc-annotate.el
+++ b/lisp/vc/vc-annotate.el
@@ -409,7 +409,9 @@ vc-annotate
 				  nil nil "20")))))))
   (vc-ensure-vc-buffer)
   (setq vc-annotate-display-mode display-mode) ;Not sure why.  --Stef
-  (let* ((temp-buffer-name (format "*Annotate %s (rev %s)*" (buffer-name) rev))
+  (let* ((temp-buffer-name (format "*Annotate %s (rev %s)*" (buffer-name)
+                                   (vc-call-backend (vc-backend file)
+                                                    'short-revision rev)))
          (temp-buffer-show-function 'vc-annotate-display-select)
          ;; If BUF is specified, we presume the caller maintains current line,
          ;; so we don't need to do it here.  This implementation may give
diff --git a/lisp/vc/vc-git.el b/lisp/vc/vc-git.el
index 707fc7cfc07..2ff6f5564ed 100644
--- a/lisp/vc/vc-git.el
+++ b/lisp/vc/vc-git.el
@@ -403,6 +403,11 @@ vc-git-working-revision
   (let (process-file-side-effects)
     (vc-git--rev-parse "HEAD")))
 
+(defun vc-git-short-revision (rev)
+  "Git-specific version of `vc-short-revision'."
+  (let (process-file-side-effects)
+    (vc-git--rev-parse rev 'short)))
+
 (defun vc-git--symbolic-ref (file)
   (or
    (vc-file-getprop file 'vc-git-symbolic-ref)
@@ -1830,11 +1835,14 @@ vc-git-previous-revision
     ;; does not (and cannot) quote.
     (vc-git--rev-parse (concat rev "~1"))))
 
-(defun vc-git--rev-parse (rev)
+(defun vc-git--rev-parse (rev &optional short)
   (with-temp-buffer
     (and
-     (vc-git--out-ok "rev-parse" rev)
-     (buffer-substring-no-properties (point-min) (+ (point-min) 40)))))
+     (apply #'vc-git--out-ok "rev-parse"
+            (append (when short '("--short"))
+                    (list rev)))
+     (goto-char (point-min))
+     (buffer-substring-no-properties (point) (pos-eol)))))
 
 (defun vc-git-next-revision (file rev)
   "Git-specific version of `vc-next-revision'."
diff --git a/lisp/vc/vc-hooks.el b/lisp/vc/vc-hooks.el
index c16fb63b2ff..38c84a0ceea 100644
--- a/lisp/vc/vc-hooks.el
+++ b/lisp/vc/vc-hooks.el
@@ -502,6 +502,11 @@ vc-working-revision
                            (vc-call-backend
                             backend 'working-revision file))))))
 
+(defun vc-default-short-revision (_backend rev)
+  "Return a \"shortened\" version of the revision REV.
+This default implementation simply returns REV unchanged."
+  rev)
+
 (defun vc-default-registered (backend file)
   "Check if FILE is registered in BACKEND using vc-BACKEND-master-templates."
   (let ((sym (vc-make-backend-sym backend 'master-templates)))
-- 
2.25.1