prepush: rewrite most of the code from scratch

For servers with branchmap support, the algorithm now works as follows:

1. A list of branches in outgoing changesets is created.
2. Using the remote branchmap, a check for new branches is performed.
3. A map (from branch to head list) of locally known remote heads before
   the push is created, and one which, after step 4, will contain the locally
   known remote heads after the push.
4. The post-push head map is updated with the outgoing changesets, using the
   branch cache update mechanism.
5. A check for new heads is performed, by comparing the length of the head list
   before and after push, for each branch. If there are new heads, an error
   depending on whether or not there are incoming changes on the branch,
   is returned.
6. If the push is allowed, a warning is written if there are incoming changes
   on any branches involved in the push.

For old servers, an algorithm similar to step 4-6 above is used to check for
new topological heads only.

Two bugs are also fixed:
1. Sometimes you would be allowed to push new branch heads without --force.
   A test for this case was added.
2. You would get the "note: unsynced remote changes!" warning if there were any
   incoming changesets, even if they were on unrelated branches.

mercurial/localrepo.py

@@ -1500,64 +1500,32 class localrepository(repo.repository):
         remote_heads = remote.heads()
         inc = self.findincoming(remote, common, remote_heads, force=force)
 
+        cl = self.changelog
         update, updated_heads = self.findoutgoing(remote, common, remote_heads)
-        msng_cl, bases, heads = self.changelog.nodesbetween(update, revs)
-
-        def checkbranch(lheads, rheads, lheadcnt, branchname=None):
-            '''
-            check whether there are more local heads than remote heads on
-            a specific branch.
-
-            lheads: local branch heads
-            rheads: remote branch heads
-            lheadcnt: total number of local branch heads
-            '''
-
-            warn = 0
-
-            if len(lheads) > len(rheads):
-                warn = 1
-            else:
-                # add local heads involved in the push
-                updatelheads = [self.changelog.heads(x, lheads)
-                                for x in update]
-                newheads = set(sum(updatelheads, [])) & set(lheads)
-
-                if not newheads:
-                    return True
-
-                # add heads we don't have or that are not involved in the push
-                for r in rheads:
-                    if r in self.changelog.nodemap:
-                        desc = self.changelog.heads(r, heads)
-                        l = [h for h in heads if h in desc]
-                        if not l:
-                            newheads.add(r)
-                    else:
-                        newheads.add(r)
-                if len(newheads) > len(rheads):
-                    warn = 1
-
-            if warn:
-                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 lheadcnt > 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
+        outg, bases, heads = cl.nodesbetween(update, revs)
 
         if not bases:
             self.ui.status(_("no changes found\n"))
             return None, 1
-        elif not force:
+
+        if not force and remote_heads != [nullid]:
+
+            def fail_multiple_heads(unsynced, branch=None):
+                if branch:
+                    msg = _("abort: push creates new remote heads"
+                            " on branch '%s'!\n") % branch
+                else:
+                    msg = _("abort: push creates new remote heads!\n")
+                self.ui.warn(msg)
+                if unsynced:
+                    self.ui.status(_("(you should pull and merge or"
+                                     " use push -f to force)\n"))
+                else:
+                    self.ui.status(_("(did you forget to merge?"
+                                     " use push -f to force)\n"))
+                return None, 0
+
+            if remote.capable('branchmap'):
             # Check for each named branch if we're creating new remote heads.
             # To be a remote head after push, node must be either:
             # - unknown locally
@@ -1567,44 +1535,72 class localrepository(repo.repository):
             #
             # New named branches cannot be created without --force.
 
-            if remote_heads != [nullid]:
-                if remote.capable('branchmap'):
-                    remotebrheads = remote.branchmap()
+                # 1. Create set of branches involved in the push.
+                branches = set(self[n].branch() for n in outg)
 
-                    lbrmap = self.branchmap()
-                    localbrheads = {}
-                    if not revs:
-                        for br, hds in lbrmap.iteritems():
-                            localbrheads[br] = (len(hds), hds)
-                    else:
-                        ctxgen = (self[n] for n in msng_cl)
-                        self._updatebranchcache(localbrheads, ctxgen)
-                        for br, hds in localbrheads.iteritems():
-                            localbrheads[br] = (len(lbrmap[br]), hds)
-
-                    newbranches = list(set(localbrheads) - set(remotebrheads))
+                # 2. Check for new branches on the remote.
+                remotemap = remote.branchmap()
+                newbranches = branches - set(remotemap)
                     if newbranches: # new branch requires --force
                         branchnames = ', '.join("%s" % b for b in newbranches)
                         self.ui.warn(_("abort: push creates "
                                        "new remote branches: %s!\n")
                                      % branchnames)
-                        # propose 'push -b .' in the msg too?
                         self.ui.status(_("(use 'hg push -f' to force)\n"))
                         return None, 0
-                    for branch, x in localbrheads.iteritems():
-                        if branch in remotebrheads:
-                            headcnt, lheads = x
-                            rheads = remotebrheads[branch]
-                            if not checkbranch(lheads, rheads, headcnt, branch):
-                                return None, 0
+
+                # 3. Construct the initial oldmap and newmap dicts.
+                # They contain information about the remote heads before and
+                # after the push, respectively.
+                # Heads not found locally are not included in either dict,
+                # since they won't be affected by the push.
+                # unsynced contains all branches with incoming changesets.
+                oldmap = {}
+                newmap = {}
+                unsynced = set()
+                for branch in branches:
+                    remoteheads = remotemap[branch]
+                    prunedheads = [h for h in remoteheads if h in cl.nodemap]
+                    oldmap[branch] = prunedheads
+                    newmap[branch] = list(prunedheads)
+                    if len(remoteheads) > len(prunedheads):
+                        unsynced.add(branch)
+
+                # 4. Update newmap with outgoing changes.
+                # This will possibly add new heads and remove existing ones.
+                ctxgen = (self[n] for n in outg)
+                self._updatebranchcache(newmap, ctxgen)
+
+                # 5. Check for new heads.
+                # If there are more heads after the push than before, a suitable
+                # warning, depending on unsynced status, is displayed.
+                for branch in branches:
+                    if len(newmap[branch]) > len(oldmap[branch]):
+                        return fail_multiple_heads(branch in unsynced, branch)
+
+                # 6. Check for unsynced changes on involved branches.
+                if unsynced:
+                    self.ui.warn(_("note: unsynced remote changes!\n"))
+
                 else:
-                    if not checkbranch(heads, remote_heads, len(heads)):
-                        return None, 0
-
+                # Old servers: Check for new topological heads.
+                # Code based on _updatebranchcache.
+                newheads = set(h for h in remote_heads if h in cl.nodemap)
+                oldheadcnt = len(newheads)
+                newheads.update(outg)
+                if len(newheads) > 1:
+                    for latest in reversed(outg):
+                        if latest not in newheads:
+                            continue
+                        minhrev = min(cl.rev(h) for h in newheads)
+                        reachable = cl.reachable(latest, cl.node(minhrev))
+                        reachable.remove(latest)
+                        newheads.difference_update(reachable)
+                if len(newheads) > oldheadcnt:
+                    return fail_multiple_heads(inc)
             if inc:
                 self.ui.warn(_("note: unsynced remote changes!\n"))
 
-
         if revs is None:
             # use the fast path, no race possible on push
             nodes = self.changelog.findmissing(common.keys())

tests/test-push-warn

@@ -298,6 +298,8 hg glog -R inner --template "{rev}: {bra
 echo %% outgoing
 hg out inner --template "{rev}: {branches} {desc}\n"
 hg push inner
+hg push inner -r4 -r5
+hg in inner
 cd ..
 
 exit 0

tests/test-push-warn.out

@@ -211,7 +211,6 searching for changes
 2: A a2
 pushing to inner
 searching for changes
-note: unsynced remote changes!
 adding changesets
 adding manifests
 adding file changes
@@ -253,7 +252,6 searching for changes
 3: A a2
 pushing to inner
 searching for changes
-note: unsynced remote changes!
 adding changesets
 adding manifests
 adding file changes
@@ -303,3 +301,10 pushing to inner
 searching for changes
 abort: push creates new remote heads on branch 'A'!
 (did you forget to merge? use push -f to force)
+pushing to inner
+searching for changes
+abort: push creates new remote heads on branch 'A'!
+(did you forget to merge? use push -f to force)
+comparing with inner
+searching for changes
+no changes found