histedit: save manually edited commit message into ".hg/last-message.txt"

Before this patch, manually edited commit message for "message"
command in histedit-ing is not saved into ".hg/last-message.txt" until
it is saved by "localrepository.savecommitmessage()" in
"localrepository.commit()".

This may lose such commit message, if unexpected exception is raised.

This patch saves manually edited commit message for "message" comand
in histedit-ing into ".hg/last-message.txt" just after user editing.

This is the simplest implementation to fix on stable. Editing and
saving commit message should be centralized into the framework of
"localrepository.commit()" with "editor" argument in the future.

This patch uses repository wrapping class for exception raising before
saving commit message in "localrepository.commit()" easily and
certainly, because such exception requires corner case condition.

hgext/histedit.py

@@ -398,6 +398,7 b' def message(ui, repo, ctx, ha, opts):'
             _('Fix up the change and run hg histedit --continue'))
     message = oldctx.description() + '\n'
     message = ui.edit(message, ui.username())
+    repo.savecommitmessage(message)
     commit = commitfuncfor(repo, oldctx)
     new = commit(text=message, user=oldctx.user(), date=oldctx.date(),
                  extra=oldctx.extra())

tests/test-histedit-edit.t

@@ -189,6 +189,49 b" say we'll change the message, but don't."
   
 
 modify the message
+
+check saving last-message.txt, at first
+
+  $ cat > $TESTTMP/commitfailure.py <<EOF
+  > from mercurial import util
+  > def reposetup(ui, repo):
+  >     class commitfailure(repo.__class__):
+  >         def commit(self, *args, **kwargs):
+  >             raise util.Abort('emulating unexpected abort')
+  >     repo.__class__ = commitfailure
+  > EOF
+  $ cat > .hg/hgrc <<EOF
+  > [extensions]
+  > commitfailure = $TESTTMP/commitfailure.py
+  > EOF
+
+  $ cat > $TESTTMP/editor.sh <<EOF
+  > echo "==== before editing"
+  > cat \$1
+  > echo "===="
+  > echo "check saving last-message.txt" >> \$1
+  > EOF
+  $ rm -f .hg/last-message.txt
+  $ HGEDITOR="sh $TESTTMP/editor.sh" hg histedit tip --commands - 2>&1 << EOF | fixbundle
+  > mess 1fd3b2fe7754 f
+  > EOF
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  ==== before editing
+  f
+  ====
+  abort: emulating unexpected abort
+  $ cat .hg/last-message.txt
+  f
+  check saving last-message.txt
+
+  $ cat > .hg/hgrc <<EOF
+  > [extensions]
+  > commitfailure = !
+  > EOF
+  $ hg histedit --abort -q
+
+then, check "modify the message" itself
+
   $ hg histedit tip --commands - 2>&1 << EOF | fixbundle
   > mess 1fd3b2fe7754 f
   > EOF