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+++ b/mercurial/repair.py
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+# repair.py - functions for repository repair for mercurial
+#
+# Copyright 2005, 2006 Chris Mason <mason@suse.com>
+# Copyright 2007 Matt Mackall
+#
+# This software may be used and distributed according to the terms
+# of the GNU General Public License, incorporated herein by reference.
+
+import changegroup, revlog, os, commands
+
+def strip(ui, repo, rev, backup="all"):
+    def limitheads(chlog, stop):
+        """return the list of all nodes that have no children"""
+        p = {}
+        h = []
+        stoprev = 0
+        if stop in chlog.nodemap:
+            stoprev = chlog.rev(stop)
+
+        for r in xrange(chlog.count() - 1, -1, -1):
+            n = chlog.node(r)
+            if n not in p:
+                h.append(n)
+            if n == stop:
+                break
+            if r < stoprev:
+                break
+            for pn in chlog.parents(n):
+                p[pn] = 1
+        return h
+
+    def bundle(repo, bases, heads, rev, suffix):
+        cg = repo.changegroupsubset(bases, heads, 'strip')
+        backupdir = repo.join("strip-backup")
+        if not os.path.isdir(backupdir):
+            os.mkdir(backupdir)
+        name = os.path.join(backupdir, "%s-%s" % (revlog.short(rev), suffix))
+        ui.warn("saving bundle to %s\n" % name)
+        return changegroup.writebundle(cg, name, "HG10BZ")
+
+    def stripall(revnum):
+        mm = repo.changectx(rev).manifest()
+        seen = {}
+
+        for x in xrange(revnum, repo.changelog.count()):
+            for f in repo.changectx(x).files():
+                if f in seen:
+                    continue
+                seen[f] = 1
+                if f in mm:
+                    filerev = mm[f]
+                else:
+                    filerev = 0
+                seen[f] = filerev
+        # we go in two steps here so the strip loop happens in a
+        # sensible order.  When stripping many files, this helps keep
+        # our disk access patterns under control.
+        seen_list = seen.keys()
+        seen_list.sort()
+        for f in seen_list:
+            ff = repo.file(f)
+            filerev = seen[f]
+            if filerev != 0:
+                if filerev in ff.nodemap:
+                    filerev = ff.rev(filerev)
+                else:
+                    filerev = 0
+            ff.strip(filerev, revnum)
+
+    chlog = repo.changelog
+    # TODO delete the undo files, and handle undo of merge sets
+    pp = chlog.parents(rev)
+    revnum = chlog.rev(rev)
+
+    # save is a list of all the branches we are truncating away
+    # that we actually want to keep.  changegroup will be used
+    # to preserve them and add them back after the truncate
+    saveheads = []
+    savebases = {}
+
+    heads = limitheads(chlog, rev)
+    seen = {}
+
+    # search through all the heads, finding those where the revision
+    # we want to strip away is an ancestor.  Also look for merges
+    # that might be turned into new heads by the strip.
+    while heads:
+        h = heads.pop()
+        n = h
+        while True:
+            seen[n] = 1
+            pp = chlog.parents(n)
+            if pp[1] != revlog.nullid:
+                for p in pp:
+                    if chlog.rev(p) > revnum and p not in seen:
+                        heads.append(p)
+            if pp[0] == revlog.nullid:
+                break
+            if chlog.rev(pp[0]) < revnum:
+                break
+            n = pp[0]
+            if n == rev:
+                break
+        r = chlog.reachable(h, rev)
+        if rev not in r:
+            saveheads.append(h)
+            for x in r:
+                if chlog.rev(x) > revnum:
+                    savebases[x] = 1
+
+    # create a changegroup for all the branches we need to keep
+    if backup == "all":
+        bundle(repo, [rev], chlog.heads(), rev, 'backup')
+    if saveheads:
+        chgrpfile = bundle(repo, savebases.keys(), saveheads, rev, 'temp')
+
+    stripall(revnum)
+
+    change = chlog.read(rev)
+    chlog.strip(revnum, revnum)
+    repo.manifest.strip(repo.manifest.rev(change[0]), revnum)
+    if saveheads:
+        ui.status("adding branch\n")
+        commands.unbundle(ui, repo, "file:%s" % chgrpfile, update=False)
+        if backup != "strip":
+            os.unlink(chgrpfile)
+