prepush: add more precise error messages

Part of the patch is from [e-mail]

- indicate the branch name where there are multiple heads
- give better advice when hitting a possible race, where new heads are added
  between discovery and the call to branchmap(). In that case, asking the user
  to merge isn't helpful, since only remote has the changes.

mercurial/localrepo.py

@@ -1491,7 +1491,7 b' class localrepository(repo.repository):'
         update, updated_heads = self.findoutgoing(remote, common, remote_heads)
         msng_cl, bases, heads = self.changelog.nodesbetween(update, revs)
 
-        def checkbranch(lheads, rheads, updatelb):
+        def checkbranch(lheads, rheads, updatelb, branchname=None):
             '''
             check whether there are more local heads than remote heads on
             a specific branch.
@@ -1527,9 +1527,18 b' class localrepository(repo.repository):'
                     warn = 1
 
             if warn:
-                self.ui.warn(_("abort: push creates new remote heads!\n"))
+                if branchname is not None:
+                    msg = _("abort: push creates new remote heads"
+                            " on branch '%s'!\n") % branchname
+                else:
+                    msg = _("abort: push creates new remote heads!\n")
+                self.ui.warn(msg)
+                if len(lheads) > len(rheads):
                 self.ui.status(_("(did you forget to merge?"
                                  " use push -f to force)\n"))
+                else:
+                    self.ui.status(_("(you should pull and merge or"
+                                     " use push -f to force)\n"))
                 return False
             return True
 
@@ -1570,7 +1579,7 b' class localrepository(repo.repository):'
                     for branch, lheads in localbrheads.iteritems():
                         if branch in remotebrheads:
                             rheads = remotebrheads[branch]
-                            if not checkbranch(lheads, rheads, update):
+                            if not checkbranch(lheads, rheads, update, branch):
                                 return None, 0
                 else:
                     if not checkbranch(heads, remote_heads, update):

tests/test-push-warn.out

@@ -2,8 +2,8 b' updating to branch default'
 1 files updated, 0 files merged, 0 files removed, 0 files unresolved
 pushing to ../a
 searching for changes
-abort: push creates new remote heads!
-(did you forget to merge? use push -f to force)
+abort: push creates new remote heads on branch 'default'!
+(you should pull and merge or use push -f to force)
 pulling from ../a
 searching for changes
 adding changesets
@@ -13,7 +13,7 b' added 1 changesets with 1 changes to 1 f'
 (run 'hg heads' to see heads, 'hg merge' to merge)
 pushing to ../a
 searching for changes
-abort: push creates new remote heads!
+abort: push creates new remote heads on branch 'default'!
 (did you forget to merge? use push -f to force)
 1 files updated, 0 files merged, 0 files removed, 0 files unresolved
 (branch merge, don't forget to commit)
@@ -35,7 +35,7 b' 0 files updated, 1 files merged, 0 files'
 (branch merge, don't forget to commit)
 pushing to ../c
 searching for changes
-abort: push creates new remote heads!
+abort: push creates new remote heads on branch 'default'!
 (did you forget to merge? use push -f to force)
 1
 pushing to ../c
@@ -44,12 +44,12 b' no changes found'
 0
 pushing to ../c
 searching for changes
-abort: push creates new remote heads!
-(did you forget to merge? use push -f to force)
+abort: push creates new remote heads on branch 'default'!
+(you should pull and merge or use push -f to force)
 1
 pushing to ../c
 searching for changes
-abort: push creates new remote heads!
+abort: push creates new remote heads on branch 'default'!
 (did you forget to merge? use push -f to force)
 1
 pushing to ../c
@@ -106,8 +106,8 b' 1'
 % fail on multiple head push
 pushing to ../f
 searching for changes
-abort: push creates new remote heads!
-(did you forget to merge? use push -f to force)
+abort: push creates new remote heads on branch 'a'!
+(you should pull and merge or use push -f to force)
 1
 % push replacement head on existing branches
 pushing to ../f
@@ -153,8 +153,8 b' adding c'
 created new head
 pushing to h
 searching for changes
-abort: push creates new remote heads!
-(did you forget to merge? use push -f to force)
+abort: push creates new remote heads on branch 'default'!
+(you should pull and merge or use push -f to force)
 
 % check prepush logic with merged branches
 marked working directory as branch a
@@ -167,6 +167,6 b' 1 files updated, 0 files merged, 0 files'
 (branch merge, don't forget to commit)
 pushing to j
 searching for changes
-abort: push creates new remote heads!
-(did you forget to merge? use push -f to force)
+abort: push creates new remote heads on branch 'a'!
+(you should pull and merge or use push -f to force)
 

tests/test-subrepo.out

@@ -151,7 +151,7 b' adding file changes'
 added 1 changesets with 1 changes to 1 files
 % push -f
 committing subrepository s
-abort: push creates new remote heads!
+abort: push creates new remote heads on branch 'default'!
 pushing ...sub/t
 pushing ...subrepo ss
 searching for changes