rebase: improve output of --dry-run

Improved output when in dryrun, for user to make sure that
no change will be written to repository.

Differential Revision: https://phab.mercurial-scm.org/D3764

hgext/rebase.py

@@ -844,6 +844,7 b' def rebase(ui, repo, **opts):'
 
 def _dryrunrebase(ui, repo, opts):
     rbsrt = rebaseruntime(repo, ui, inmemory=True, opts=opts)
+    ui.status(_('starting dry-run rebase; repository will not be changed\n'))
     with repo.wlock(), repo.lock():
         try:
             overrides = {('rebase', 'singletransaction'): True}
@@ -854,7 +855,8 b' def _dryrunrebase(ui, repo, opts):'
             ui.status(_('hit a merge conflict\n'))
             return 1
         else:
-            ui.status(_('there will be no conflict, you can rebase\n'))
+            ui.status(_('dry-run rebase completed successfully; run without '
+                        '-n/--dry-run to perform this rebase\n'))
             return 0
         finally:
             # no need to store backup in case of dryrun

tests/test-rebase-inmemory.t

@@ -208,10 +208,11 b' Make sure it throws error while passing '
 
 Check dryrun gives correct results when there is no conflict in rebasing
   $ hg rebase -s 2 -d 6 -n
+  starting dry-run rebase; repository will not be changed
   rebasing 2:177f92b77385 "c"
   rebasing 3:055a42cdd887 "d"
   rebasing 4:e860deea161a "e"
-  there will be no conflict, you can rebase
+  dry-run rebase completed successfully; run without -n/--dry-run to perform this rebase
 
   $ hg diff
   $ hg status
@@ -240,10 +241,11 b' Check dryrun gives correct results when '
   
 Check dryrun working with --collapse when there is no conflict
   $ hg rebase -s 2 -d 6 -n --collapse
+  starting dry-run rebase; repository will not be changed
   rebasing 2:177f92b77385 "c"
   rebasing 3:055a42cdd887 "d"
   rebasing 4:e860deea161a "e"
-  there will be no conflict, you can rebase
+  dry-run rebase completed successfully; run without -n/--dry-run to perform this rebase
 
 Check dryrun gives correct results when there is conflict in rebasing
 Make a conflict:
@@ -276,6 +278,7 b' Make a conflict:'
      a
   
   $ hg rebase -s 2 -d 7 -n
+  starting dry-run rebase; repository will not be changed
   rebasing 2:177f92b77385 "c"
   rebasing 3:055a42cdd887 "d"
   rebasing 4:e860deea161a "e"
@@ -313,6 +316,7 b' Make a conflict:'
   
 Check dryrun working with --collapse when there is conflicts
   $ hg rebase -s 2 -d 7 -n --collapse
+  starting dry-run rebase; repository will not be changed
   rebasing 2:177f92b77385 "c"
   rebasing 3:055a42cdd887 "d"
   rebasing 4:e860deea161a "e"