Simplify handling of parents of exported commit

The previous code did an awful lot of work to infer the parents of an
exported commit, incorporating information from many sources.  But
there were multiple bugs in this scheme, sometimes resulting in merge
commits with two parents pointing to the same commit object.

Instead, use a much more straightforward process of mapping the
parents stored in hg.

hg-fast-export.py

@@ -36,11 +36,10 @@ def checkpoint(count):
     wr()
   return count
 
-def get_parent_mark(parent,marks):
-  """Get the mark for some parent.
-  If we saw it in the current session, return :%d syntax and
-  otherwise the SHA1 from the cache."""
-  return marks.get(str(parent),':%d' % (parent+1))
+def revnum_to_revref(rev, old_marks):
+  """Convert an hg revnum to a git-fast-import rev reference (an SHA1
+  or a mark)"""
+  return old_marks.get(rev) or ':%d' % (rev+1)
 
 def file_mismatch(f1,f2):
   """See if two revisions of a file are not equal."""
@@ -131,13 +130,6 @@ def export_file_contents(ctx,manifest,files):
   if max>cfg_export_boundary:
     sys.stderr.write('Exported %d/%d files\n' % (count,max))
 
-def is_merge(parents):
-  c=0
-  for parent in parents:
-    if parent>=0:
-      c+=1
-  return c>1
-
 def sanitize_name(name,what="branch"):
   """Sanitize input roughly according to git-check-ref-format(1)"""
 
@@ -157,7 +149,7 @@ def sanitize_name(name,what="branch"):
     sys.stderr.write('Warning: sanitized %s [%s] to [%s]\n' % (what,name,n))
   return n
 
-def export_commit(ui,repo,revision,marks,mapping,heads,last,max,count,authors,sob,brmap):
+def export_commit(ui,repo,revision,old_marks,max,count,authors,sob,brmap):
   def get_branchname(name):
     if brmap.has_key(name):
       return brmap[name]
@@ -166,7 +158,6 @@ def export_commit(ui,repo,revision,marks,mapping,heads,last,max,count,authors,so
     return n
 
   (revnode,_,user,(time,timezone),files,desc,branch,_)=get_changeset(ui,repo,revision,authors)
-  parents=repo.changelog.parentrevs(revision)
 
   branch=get_branchname(branch)
 
@@ -179,75 +170,38 @@ def export_commit(ui,repo,revision,marks,mapping,heads,last,max,count,authors,so
   wr(desc)
   wr()
 
-  pidx1, pidx2 = 0, 1
-  if parents[1] > 0:
-    if parents[0] <= 0 or \
-        repo.changelog.node(parents[0]) < repo.changelog.node(parents[1]):
-      pidx1, pidx2 = 1, 0
+  parents = [p for p in repo.changelog.parentrevs(revision) if p >= 0]
 
-  full_rev=False
-  if revision==0: full_rev=True
-
-  src=heads.get(branch,'')
-  link=''
-  if src!='':
-    # if we have a cached head, this is an incremental import: initialize it
-    # and kill reference so we won't init it again
-    wr('from %s' % src)
-    heads[branch]=''
-    sys.stderr.write('%s: Initializing to parent [%s]\n' %
-        (branch,src))
-    link=src # avoid making a merge commit for incremental import
-  elif link=='' and not heads.has_key(branch) and revision>0:
-    if parents[0]>=0:
-      # newly created branch with parent: connect to parent
-      tmp=get_parent_mark(parents[0],marks)
-      wr('from %s' % tmp)
-      sys.stderr.write('%s: Link new branch to parent [%s]\n' %
-          (branch,tmp))
-      link=tmp # avoid making a merge commit for branch fork
-    else:
-      # newly created branch without parent: feed full revision
-      full_rev=True
-  elif last.get(branch,revision) != parents[pidx1] and parents[pidx1] > 0 and revision > 0:
-    pm=get_parent_mark(parents[pidx1],marks)
-    sys.stderr.write('%s: Placing commit [r%d] in branch [%s] on top of [r%d]\n' %
-        (branch,revision,branch,parents[pidx1]));
-    wr('from %s' % pm)
-
-  if parents[pidx2] > 0:
-    pm=get_parent_mark(parents[pidx2],marks)
-    sys.stderr.write('%s: Merging with parent [%s] from [r%d]\n' %
-        (branch,pm,parents[pidx2]))
-    wr('merge %s' % pm)
-
-  last[branch]=revision
-  heads[branch]=''
-  # we need this later to write out tags
-  marks[str(revision)]=':%d'%(revision+1)
+  # Sort the parents based on revision ids so that we always get the
+  # same resulting git repo, no matter how the revisions were
+  # numbered.
+  parents.sort(key=repo.changelog.node, reverse=True)
 
   ctx=repo.changectx(str(revision))
   man=ctx.manifest()
   added,changed,removed,type=[],[],[],''
 
-  if full_rev:
+  if len(parents) == 0:
     # first revision: feed in full manifest
     added=man.keys()
     added.sort()
     type='full'
-  elif is_merge(parents):
-    # later merge revision: feed in changed manifest
-    # for many files comparing checksums is expensive so only do it for
-    # merges where we really need it due to hg's revlog logic
-    added,changed,removed=get_filechanges(repo,revision,parents,man)
-    type='thorough delta'
   else:
-    # later non-merge revision: feed in changed manifest
-    # if we have exactly one parent, just take the changes from the
-    # manifest without expensively comparing checksums
-    f=repo.status(repo.lookup(parents[0]),revnode)[:3]
-    added,changed,removed=f[1],f[0],f[2]
-    type='simple delta'
+    wr('from %s' % revnum_to_revref(parents[0], old_marks))
+    if len(parents) == 1:
+      # later non-merge revision: feed in changed manifest
+      # if we have exactly one parent, just take the changes from the
+      # manifest without expensively comparing checksums
+      f=repo.status(repo.lookup(parents[0]),revnode)[:3]
+      added,changed,removed=f[1],f[0],f[2]
+      type='simple delta'
+    else: # a merge with two parents
+      wr('merge %s' % revnum_to_revref(parents[1], old_marks))
+      # later merge revision: feed in changed manifest
+      # for many files comparing checksums is expensive so only do it for
+      # merges where we really need it due to hg's revlog logic
+      added,changed,removed=get_filechanges(repo,revision,parents,man)
+      type='thorough delta'
 
   sys.stderr.write('%s: Exporting %s revision %d/%d with %d/%d/%d added/changed/removed files\n' %
       (branch,type,revision+1,max,len(added),len(changed),len(removed)))
@@ -259,7 +213,7 @@ def export_commit(ui,repo,revision,marks,mapping,heads,last,max,count,authors,so
 
   return checkpoint(count)
 
-def export_tags(ui,repo,marks_cache,mapping_cache,count,authors):
+def export_tags(ui,repo,old_marks,mapping_cache,count,authors):
   l=repo.tagslist()
   for tag,node in l:
     tag=sanitize_name(tag,"tag")
@@ -272,7 +226,7 @@ def export_tags(ui,repo,marks_cache,mapping_cache,count,authors):
 
     rev=int(mapping_cache[node.encode('hex_codec')])
 
-    ref=marks_cache.get(str(rev),':%d' % (rev))
+    ref=revnum_to_revref(rev, old_marks)
     if ref==None:
       sys.stderr.write('Failed to find reference for creating tag'
           ' %s at r%d\n' % (tag,rev))
@@ -332,13 +286,10 @@ def verify_heads(ui,repo,cache,force):
 
   return True
 
-def mangle_mark(mark):
-  return str(int(mark)-1)
-
 def hg2git(repourl,m,marksfile,mappingfile,headsfile,tipfile,authors={},sob=False,force=False):
   _max=int(m)
 
-  marks_cache=load_cache(marksfile,mangle_mark)
+  old_marks=load_cache(marksfile,lambda s: int(s)-1)
   mapping_cache=load_cache(mappingfile)
   heads_cache=load_cache(headsfile)
   state_cache=load_cache(tipfile)
@@ -364,17 +315,16 @@ def hg2git(repourl,m,marksfile,mappingfile,headsfile,tipfile,authors={},sob=Fals
 
 
   c=0
-  last={}
   brmap={}
   for rev in range(min,max):
-    c=export_commit(ui,repo,rev,marks_cache,mapping_cache,heads_cache,last,max,c,authors,sob,brmap)
+    c=export_commit(ui,repo,rev,old_marks,max,c,authors,sob,brmap)
 
   state_cache['tip']=max
   state_cache['repo']=repourl
   save_cache(tipfile,state_cache)
   save_cache(mappingfile,mapping_cache)
 
-  c=export_tags(ui,repo,marks_cache,mapping_cache,c,authors)
+  c=export_tags(ui,repo,old_marks,mapping_cache,c,authors)
 
   sys.stderr.write('Issued %d commands\n' % c)