bug#73232: [PATCH] Allow vc-diff to suggest a default revision in vc-dir

[Spencer Baugh via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

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Tags: patch


C-u M-x vc-root-diff will prompt for the old revision to use for the
diff.  The prompt will have a default calculated by
vc-diff-build-argument-list-internal.  The default is either the
working revision of the current fileset or the revision before that.

vc-diff-build-argument-list-internal contained a check (added in
c0d66cb21bac57f5ec0378e8a04aac8f35c3eb5c) which explicitly avoided
setting a default if the current fileset was a directory.  This check
was added in 1997 when vc only worked for single files.

This prevents a backend from choosing to return a non-nil value from
'working-revision when passed a directory.  (The vc-hg and vc-git
backends, at least, will do this)

Allow this by moving the file-directory-p check, so that we try
calling 'working-revision when the fileset is a single directory.  The
call is in inside ignore-errors, so if a backend errors when passed a
directory, we'll just get no default, as before.  (Most backends will
just return nil for a directory, rather than erroring)

Also, while we're here, explicitly pass the backend to
vc-working-revision rather than having vc-working-revision recompute
it.

Concretely this has the effect that for the vc-git and vc-hg backends,
running C-u M-x vc-root-diff in vc-dir will have the same behavior as
running C-u M-x vc-root-diff in a clean file: The "Previous revision:"
prompt's default will be the revision before HEAD.

* lisp/vc/vc.el (vc-diff-build-argument-list-internal): Move
file-directory-p check.

In GNU Emacs 29.2.50 (build 17, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.15.12, Xaw scroll bars) of 2024-09-06 built on
 igm-qws-u22796a
Repository revision: e6d04c06a7eb6ce932b52a346368d02b7a811a00
Repository branch: emacs-29
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: Rocky Linux 8.10 (Green Obsidian)

Configured using:
 'configure --with-x-toolkit=lucid --without-gpm --without-gconf
 --without-selinux --without-imagemagick --with-modules --with-gif=no
 --with-cairo --with-rsvg --without-compress-install
 --with-native-compilation=aot --with-tree-sitter
 PKG_CONFIG_PATH=/usr/local/home/garnish/libtree-sitter/0.22.6-1/lib/pkgconfig/'


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From e57db4d91cf098d26c8c131d715ef3619466d159 Mon Sep 17 00:00:00 2001
From: Spencer Baugh <sbaugh@janestreet.com>
Date: Fri, 13 Sep 2024 11:34:55 -0400
Subject: [PATCH] Allow vc-diff to suggest a default revision in vc-dir

C-u M-x vc-root-diff will prompt for the old revision to use for the
diff.  The prompt will have a default calculated by
vc-diff-build-argument-list-internal.  The default is either the
working revision of the current fileset or the revision before that.

vc-diff-build-argument-list-internal contained a check (added in
c0d66cb21bac57f5ec0378e8a04aac8f35c3eb5c) which explicitly avoided
setting a default if the current fileset was a single directory.  This
check was added in 1997 when vc only worked for single files.

This prevents a backend from choosing to return a non-nil value from
'working-revision when passed a directory.  (The vc-hg and vc-git
backends, at least, will do this)

Allow this by moving the file-directory-p check, so that we try
calling 'working-revision when the fileset is a single directory.  The
call is in inside ignore-errors, so if a backend errors when passed a
directory, we'll just get no default, as before.  (Most backends will
just return nil for a directory, rather than erroring)

Also, while we're here, explicitly pass the backend to
vc-working-revision rather than having vc-working-revision recompute
it.

Concretely this has the effect that for the vc-git and vc-hg backends,
running C-u M-x vc-root-diff in vc-dir will have the same behavior as
running C-u M-x vc-root-diff in a clean file: The "Previous revision:"
prompt's default will be the revision before HEAD.

* lisp/vc/vc.el (vc-diff-build-argument-list-internal): Move
file-directory-p check.
---
 lisp/vc/vc.el | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/lisp/vc/vc.el b/lisp/vc/vc.el
index 597a1622f5a..d88a655dc6b 100644
--- a/lisp/vc/vc.el
+++ b/lisp/vc/vc.el
@@ -2074,17 +2074,14 @@ vc-diff-build-argument-list-internal
      ;; filesets, but not yet.
      ((/= (length files) 1)
       nil)
-     ;; if it's a directory, don't supply any revision default
-     ((file-directory-p first)
-      nil)
      ;; if the file is not up-to-date, use working revision as older revision
-     ((not (vc-up-to-date-p first))
-      (setq rev1-default (vc-working-revision first)))
+     ((not (and (file-directory-p first) (vc-up-to-date-p first)))
+      (setq rev1-default (vc-working-revision first backend)))
      ;; if the file is not locked, use last revision and current source as defaults
      (t
       (setq rev1-default (ignore-errors ;If `previous-revision' doesn't work.
                            (vc-call-backend backend 'previous-revision first
-                                            (vc-working-revision first))))
+                                            (vc-working-revision first backend))))
       (when (string= rev1-default "") (setq rev1-default nil))))
     ;; construct argument list
     (let* ((rev1-prompt (format-prompt "Older revision" rev1-default))
-- 
2.39.3