mercurial/ancestor.py

subrepo: process merge substate in sorted order in submerge()

This ensures that subrepositories are pulled in a well defined
order when cloning the parent repository.

BEFORE:

  $ hg clone http://hg.gerg.ca/allextensions
  destination directory: allextensions
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 10 changesets with 20 changes to 6 files
  updating to branch default
  pulling subrepo caseguard from http://bitbucket.org/alexandru/caseguard
  real URL is https://bitbucket.org/alexandru/caseguard
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 81 changesets with 100 changes to 13 files
  pulling subrepo hg-prompt from http://bitbucket.org/sjl/hg-prompt
  real URL is https://bitbucket.org/sjl/hg-prompt
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 114 changesets with 176 changes to 35 files
  pulling subrepo hgpaste from http://bitbucket.org/birkenfeld/hgpaste
  real URL is https://bitbucket.org/birkenfeld/hgpaste
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 18 changesets with 18 changes to 2 files
  ...

AFTER:

  $ hg clone http://hg.gerg.ca/allextensions
  destination directory: allextensions
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 10 changesets with 20 changes to 6 files
  updating to branch default
  pulling subrepo Artemis from http://hg.mrzv.org/Artemis
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 55 changesets with 108 changes to 47 files
  ...

# ancestor.py - generic DAG ancestor algorithm for mercurial
#
# Copyright 2006 Matt Mackall <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

import heapq

def ancestor(a, b, pfunc):
    """
    Returns the common ancestor of a and b that is furthest from a
    root (as measured by longest path) or None if no ancestor is
    found. If there are multiple common ancestors at the same
    distance, the first one found is returned.

    pfunc must return a list of parent vertices for a given vertex
    """

    if a == b:
        return a

    a, b = sorted([a, b])

    # find depth from root of all ancestors
    # depth is stored as a negative for heapq
    parentcache = {}
    visit = [a, b]
    depth = {}
    while visit:
        vertex = visit[-1]
        pl = pfunc(vertex)
        parentcache[vertex] = pl
        if not pl:
            depth[vertex] = 0
            visit.pop()
        else:
            for p in pl:
                if p == a or p == b: # did we find a or b as a parent?
                    return p # we're done
                if p not in depth:
                    visit.append(p)
            if visit[-1] == vertex:
                # -(maximum distance of parents + 1)
                depth[vertex] = min([depth[p] for p in pl]) - 1
                visit.pop()

    # traverse ancestors in order of decreasing distance from root
    def ancestors(vertex):
        h = [(depth[vertex], vertex)]
        seen = set()
        while h:
            d, n = heapq.heappop(h)
            if n not in seen:
                seen.add(n)
                yield (d, n)
                for p in parentcache[n]:
                    heapq.heappush(h, (depth[p], p))

    def generations(vertex):
        sg, s = None, set()
        for g, v in ancestors(vertex):
            if g != sg:
                if sg:
                    yield sg, s
                sg, s = g, set((v,))
            else:
                s.add(v)
        yield sg, s

    x = generations(a)
    y = generations(b)
    gx = x.next()
    gy = y.next()

    # increment each ancestor list until it is closer to root than
    # the other, or they match
    try:
        while 1:
            if gx[0] == gy[0]:
                for v in gx[1]:
                    if v in gy[1]:
                        return v
                gy = y.next()
                gx = x.next()
            elif gx[0] > gy[0]:
                gy = y.next()
            else:
                gx = x.next()
    except StopIteration:
        return None