Publicize behavior of log-view-diff at beginning/end of active region

* lisp/vc/log-view.el (log-view-diff, log-view-diff-changeset):
* doc/emacs/maintaining.texi (VC Change Log): Document behavior of
log-view-diff at the beginning and the end of the log buffer
when the region is active.  (Bug#35624)

* lisp/vc/vc-git.el (vc-git-print-log): Insert newline at the
beginning to enable the feature of diffing with the working revision.

2 files changed, 16 insertions, 2 deletions

diff --git a/lisp/vc/log-view.el b/lisp/vc/log-view.el
index 3389264ce6e..0b57e1d5086 100644
--- a/lisp/vc/log-view.el
+++ b/lisp/vc/log-view.el
@@ -585,6 +585,13 @@ point, get the diff between the revision at point and its
 previous revision.  Otherwise, get the diff between the revisions
 where the region starts and ends.
 
+When the beginning of the region is on the top line that has no revision,
+use the current working revision as the first revision to compare.
+
+When the end of the region is on the bottom non-revision line after
+the last revision line, use the previous revision of the last
+displayed revision as the second revision to compare.
+
 Unlike `log-view-diff-changeset', this function only shows the
 part of the changeset which affected the currently considered
 file(s)."
@@ -600,6 +607,13 @@ point, get the diff between the revision at point and its
 previous revision.  Otherwise, get the diff between the revisions
 where the region starts and ends.
 
+When the beginning of the region is on the top line that has no revision,
+use the current working revision as the first revision to compare.
+
+When the end of the region is on the bottom non-revision line after
+the last revision line, use the previous revision of the last
+displayed revision as the second revision to compare.
+
 Unlike `log-view-diff' this function shows the whole changeset,
 including changes affecting other files than the currently
 considered file(s)."
diff --git a/lisp/vc/vc-git.el b/lisp/vc/vc-git.el
index 61c13026cc5..b6feb3b8d1e 100644
--- a/lisp/vc/vc-git.el
+++ b/lisp/vc/vc-git.el
@@ -1017,8 +1017,8 @@ If LIMIT is a revision string, use it as an end-revision."
     ;; If the buffer exists from a previous invocation it might be
     ;; read-only.
     (let ((inhibit-read-only t))
-      (with-current-buffer
-          buffer
+      (with-current-buffer buffer
+        (insert "\n")
         (apply 'vc-git-command buffer
                'async files
                (append