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/'