vc-checkin: Check whether the fileset or patches have changed

* lisp/vc/vc-dispatcher.el (vc-finish-logentry): Delay popping
to vc-parent-buffer until after calling the log operation.
That way if the log operation exits early, the current buffer
remains *vc-log*.
(vc-dir-marked-files, dired-get-marked-files): Declare.
(vc-dispatcher--explicit-marks-p): New function.
* lisp/vc/vc.el (vc-checkin): Check the user isn't likely to be
surprised by what is included in the checkin.  Specifically,
check whether the fileset or patches implied by vc-parent-buffer
are unchanged.
* doc/emacs/maintaining.texi (VC With A Merging VCS): Explain
how the fileset or patch string is fixed once *vc-log* pops up.

1 files changed, 17 insertions, 0 deletions

diff --git a/doc/emacs/maintaining.texi b/doc/emacs/maintaining.texi
index 12770f218ca..ea7b8794bbc 100644
--- a/doc/emacs/maintaining.texi
+++ b/doc/emacs/maintaining.texi
@@ -572,6 +572,23 @@ then applies the changes to the respective files and commits the changes
 after popping up the @file{*vc-log*} buffer to allow you to type a
 suitable commit log message.
 
+Once you type @kbd{C-x v v}, the fileset or patches cannot be changed
+without first cancelling the commit by typing @kbd{C-c C-k} in the
+@file{*vc-log*} buffer.  For example, if you change which files are
+marked in the @file{*vc-dir*} buffer after Emacs has already popped up
+the @file{*vc-log*} buffer, the old fileset will remain in effect for
+this commit.  (This is in contrast to changes made to the
+@emph{contents} of files in the fileset: all such changes will be
+included in the commit even if they are made after Emacs has popped up
+the @file{*vc-dir*} buffer.)
+
+When you cancel a commit, Emacs saves your log message.  This means that
+if you need to adjust the fileset or patches, it is easy to restart the
+commit operation again: type @w{@kbd{C-c C-k C-x v v M-p}}.  Here
+@kbd{C-c C-k} cancels the commit, @kbd{C-x v v} initiates another with
+the new fileset or patches, and finally @kbd{M-p} recalls your previous
+log message.
+
 With modern decentralized version control systems (Git, Mercurial,
 etc.), the changes are committed locally and not automatically
 propagated to the upstream repository (which is usually on a remote