checkheads: extract branchmap preprocessing

The checkheads function is far too complicated. This extract help to explicite
what part of the preprocessing are reused by the actual check.

This the first step toward a wider refactoring.

mercurial/discovery.py

@@ -149,39 +149,24 def findcommonoutgoing(repo, other, only
 
     return og
 
-def checkheads(repo, remote, outgoing, remoteheads, newbranch=False, inc=False):
-    """Check that a push won't add any outgoing head
+def _branchmapsummary(repo, remote, outgoing):
+    """compute a summary of branch and heads status before and after push
 
-    raise Abort error and display ui message as needed.
+    - oldmap:      {'branch': [heads]} mapping for remote
+    - newmap:      {'branch': [heads]} mapping for local
+    - unsynced:    set of branch that have unsynced remote changes
+    - branches:    set of all common branch pushed
+    - newbranches: list of plain new pushed branch
     """
-    if remoteheads == [nullid]:
-        # remote is empty, nothing to check.
-        return
-
     cl = repo.changelog
-    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
-        # - a local outgoing head descended from update
-        # - a remote head that's known locally and not
-        #   ancestral to an outgoing head
 
-        # 1. Create set of branches involved in the push.
+    # A. Create set of branches involved in the push.
         branches = set(repo[n].branch() for n in outgoing.missing)
-
-        # 2. Check for new branches on the remote.
         remotemap = remote.branchmap()
         newbranches = branches - set(remotemap)
-        if newbranches and not newbranch: # new branch requires --new-branch
-            branchnames = ', '.join(sorted(newbranches))
-            raise util.Abort(_("push creates new remote branches: %s!")
-                               % branchnames,
-                             hint=_("use 'hg push --new-branch' to create"
-                                    " new remote branches"))
         branches.difference_update(newbranches)
 
-        # 3. Construct the initial oldmap and newmap dicts.
+    # B. 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,
@@ -192,18 +177,23 def checkheads(repo, remote, outgoing, r
         unsynced = set()
         for branch in branches:
             remotebrheads = remotemap[branch]
+
             prunedbrheads = [h for h in remotebrheads if h in cl.nodemap]
             oldmap[branch] = prunedbrheads
             newmap[branch] = list(prunedbrheads)
             if len(remotebrheads) > len(prunedbrheads):
                 unsynced.add(branch)
 
-        # 4. Update newmap with outgoing changes.
+    # C. Update newmap with outgoing changes.
         # This will possibly add new heads and remove existing ones.
         ctxgen = (repo[n] for n in outgoing.missing)
         repo._updatebranchcache(newmap, ctxgen)
+    return oldmap, newmap, unsynced, branches, newbranches
 
-    else:
+def _oldbranchmapsummary(repo, remoteheads, outgoing, inc=False):
+    """Compute branchmapsummary for repo without branchmap support"""
+
+    cl = repo.changelog
         # 1-4b. old servers: Check for new topological heads.
         # Construct {old,new}map with branch = None (topological branch).
         # (code based on _updatebranchcache)
@@ -218,8 +208,37 def checkheads(repo, remote, outgoing, r
         newmap = {None: list(c.node() for c in r)}
         oldmap = {None: oldheads}
         unsynced = inc and branches or set()
+    return oldmap, newmap, unsynced, branches, set()
 
-    # 5. Check for new heads.
+def checkheads(repo, remote, outgoing, remoteheads, newbranch=False, inc=False):
+    """Check that a push won't add any outgoing head
+
+    raise Abort error and display ui message as needed.
+    """
+    # 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
+    # - a local outgoing head descended from update
+    # - a remote head that's known locally and not
+    #   ancestral to an outgoing head
+    if remoteheads == [nullid]:
+        # remote is empty, nothing to check.
+        return
+
+    if remote.capable('branchmap'):
+        bms = _branchmapsummary(repo, remote, outgoing)
+    else:
+        bms = _oldbranchmapsummary(repo, remoteheads, outgoing, inc)
+    oldmap, newmap, unsynced, branches, newbranches = bms
+    # 1. Check for new branches on the remote.
+    if newbranches and not newbranch:  # new branch requires --new-branch
+        branchnames = ', '.join(sorted(newbranches))
+        raise util.Abort(_("push creates new remote branches: %s!")
+                           % branchnames,
+                         hint=_("use 'hg push --new-branch' to create"
+                                " new remote branches"))
+
+    # 2. Check for new heads.
     # If there are more heads after the push than before, a suitable
     # error message, depending on unsynced status, is displayed.
     error = None