branchcache: fetch source branchcache during clone (issue3378)

Recomputing branch cache on clone may be expensive,
therefore if possible we fetch it along with the data.

- If the clone is performed by copying, we just copy branchcache file.
- If we localrepo.clone and streaming then we follow the procedure:
  1. Fetch branchmap from the remote
  2. Fetch the actual data.
  3. Find the latest rev within branch heads (tip at the time of
     branchmap fetch)
  4. Update the cache for the revs in [remotetip+1, tip]

This way we ensure that the branchcache is correct even in case
of races with commits.

mercurial/hg.py

@@ -336,6 +336,16 b' def clone(ui, peeropts, source, dest=Non'
 
             destlock = copystore(ui, srcrepo, destpath)
 
+            # Recomputing branch cache might be slow on big repos,
+            # so just copy it
+            dstcachedir = os.path.join(destpath, 'cache')
+            srcbranchcache = srcrepo.sjoin('cache/branchheads')
+            dstbranchcache = os.path.join(dstcachedir, 'branchheads')
+            if os.path.exists(srcbranchcache):
+                if not os.path.exists(dstcachedir):
+                    os.mkdir(dstcachedir)
+                util.copyfile(srcbranchcache, dstbranchcache)
+
             # we need to re-init the repo after manually copying the data
             # into it
             destpeer = peer(ui, peeropts, dest)

mercurial/localrepo.py

@@ -2472,6 +2472,12 b' class localrepository(object):'
     def stream_in(self, remote, requirements):
         lock = self.lock()
         try:
+            # Save remote branchmap. We will use it later
+            # to speed up branchcache creation
+            rbranchmap = None
+            if remote.capable("branchmap"):
+                rbranchmap = remote.branchmap()
+
             fp = remote.stream_out()
             l = fp.readline()
             try:
@@ -2532,6 +2538,17 b' class localrepository(object):'
             self._applyrequirements(requirements)
             self._writerequirements()
 
+            if rbranchmap:
+                rbheads = []
+                for bheads in rbranchmap.itervalues():
+                    rbheads.extend(bheads)
+
+                self.branchcache = rbranchmap
+                if rbheads:
+                    rtiprev = max((int(self.changelog.rev(node))
+                            for node in rbheads))
+                    self._writebranchcache(self.branchcache,
+                            self[rtiprev].node(), rtiprev)
             self.invalidate()
             return len(self.heads()) + 1
         finally:

tests/test-http-proxy.t

@@ -99,6 +99,7 b' do not use the proxy if it is in the no '
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ cat proxy.log
   * - - [*] "GET http://localhost:$HGPORT/?cmd=capabilities HTTP/1.1" - - (glob)
+  * - - [*] "GET http://localhost:$HGPORT/?cmd=branchmap HTTP/1.1" - - (glob)
   * - - [*] "GET http://localhost:$HGPORT/?cmd=stream_out HTTP/1.1" - - (glob)
   * - - [*] "GET http://localhost:$HGPORT/?cmd=listkeys HTTP/1.1" - - x-hgarg-1:namespace=bookmarks (glob)
   * - - [*] "GET http://localhost:$HGPORT/?cmd=capabilities HTTP/1.1" - - (glob)