rebase: 'hg pull --rebase' now update only if there was nothing to rebase

I recently discovered that 'hg pull --rebase' was also running an update. And it
was running it in all cases as long as the update would move the working copy
somewhere else...

This felt wrong and it actually is. This 'update' call is introduced in
92455c1d6f83. In that commit the intent is very clear. The update should happen
only when there was nothing to rebase. The implementation did not check if a
rebase was performed because, at that time, rebase would always leave you on the
top most changeset. Being on that top most changeset result in a no-op update
and the step was skipped.

However 9c78ed396075f changed rebase behavior to preserve the working copy
parent, so if we are not on a head at pull time, the code performs both a rebase
and an update.

This changeset introduce a test for this case and restore the intended behavior.

There are other issues with this custom update code but they will be addressed
in later changeset (eg: own destination logic, lack of heads warning).

I'm not super happy with the explicitly comparison 'rebase(...) == 1' but a
later series will have a cleaner way to handle it anyway (while making 'rebase'
pick its default destination like 'merge').

hgext/rebase.py

@@ -1165,15 +1165,16 b' def pullrebase(orig, ui, repo, *args, **'
                 # --source.
                 if 'source' in opts:
                     del opts['source']
-                rebase(ui, repo, **opts)
-                branch = repo[None].branch()
-                dest = repo[branch].rev()
-                if dest != repo['.'].rev():
-                    # there was nothing to rebase we force an update
-                    hg.update(repo, dest)
-                    if bookmarks.update(repo, [movemarkfrom], repo['.'].node()):
-                        ui.status(_("updating bookmark %s\n")
-                                  % repo._activebookmark)
+                if rebase(ui, repo, **opts) == _nothingtorebase():
+                    branch = repo[None].branch()
+                    dest = repo[branch].rev()
+                    if dest != repo['.'].rev():
+                        # there was nothing to rebase we force an update
+                        hg.update(repo, dest)
+                        if bookmarks.update(repo, [movemarkfrom],
+                                            repo['.'].node()):
+                            ui.status(_("updating bookmark %s\n")
+                                      % repo._activebookmark)
         finally:
             release(lock, wlock)
     else:

tests/test-rebase-pull.t

@@ -209,3 +209,60 b' pull --rebase works with bundle2 turned '
   |
   o  0: 'C1'
   
+
+pull --rebase only update if there is nothing to rebase
+
+  $ cd ../a
+  $ echo R5 > R5
+  $ hg ci -Am R5
+  adding R5
+  $ hg tglog
+  @  6: 'R5'
+  |
+  o  5: 'R4'
+  |
+  o  4: 'R3'
+  |
+  o  3: 'R2'
+  |
+  o  2: 'R1'
+  |
+  o  1: 'C2'
+  |
+  o  0: 'C1'
+  
+  $ cd ../c
+  $ echo L2 > L2
+  $ hg ci -Am L2
+  adding L2
+  $ hg up 'desc(L1)'
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  $ hg pull --rebase
+  pulling from $TESTTMP/a (glob)
+  searching for changes
+  adding changesets
+  adding manifests
+  adding file changes
+  added 1 changesets with 1 changes to 1 files (+1 heads)
+  rebasing 6:0d0727eb7ce0 "L1"
+  rebasing 7:c1f58876e3bf "L2"
+  saved backup bundle to $TESTTMP/c/.hg/strip-backup/0d0727eb7ce0-ef61ccb2-backup.hg (glob)
+  $ hg tglog
+  o  8: 'L2'
+  |
+  @  7: 'L1'
+  |
+  o  6: 'R5'
+  |
+  o  5: 'R4'
+  |
+  o  4: 'R3'
+  |
+  o  3: 'R2'
+  |
+  o  2: 'R1'
+  |
+  o  1: 'C2'
+  |
+  o  0: 'C1'
+