treediscovery: fix regression when run against older repos (issue2793)

I ran the entire test suite with "known" and "getbundle" disabled in
localrepository. This generated failures because the old findoutgoing
had always queried remote's heads explicitly and thus always got them
back in the returned heads. treediscovery.findcommonincoming now
correctly returns remote's heads in all cases.

Also adds a dedicated test for running treediscovery against a
pre-getbundle HTTP server.

tests/test-treediscovery.t

@@ -0,0 +1,278 b''
+Tests discovery against servers without getbundle support:
+
+  $ CAP=getbundle
+  $ . "$TESTDIR/notcapable"
+  $ echo '[ui]' >>$HGRCPATH
+  $ echo 'logtemplate="{rev} {node|short}: {desc} {branches}\\n"' >>$HGRCPATH
+  $ echo '[extensions]' >>$HGRCPATH
+  $ echo 'graphlog=' >>$HGRCPATH
+
+Setup HTTP server control:
+
+  $ export remote=http://localhost:$HGPORT/
+  $ start() {
+  >   echo '[web]' > $1/.hg/hgrc
+  >   echo 'push_ssl = false' >> $1/.hg/hgrc
+  >   echo 'allow_push = *' >> $1/.hg/hgrc
+  >   hg serve -R $1 -p $HGPORT -d --pid-file=hg.pid -E errors.log
+  >   cat hg.pid >> $DAEMON_PIDS
+  > }
+  $ stop() {
+  >   "$TESTDIR/killdaemons.py"
+  > }
+
+Both are empty:
+
+  $ hg init empty1
+  $ hg init empty2
+  $ start empty2
+  $ hg incoming -R empty1 $remote
+  comparing with http://localhost:$HGPORT/
+  no changes found
+  [1]
+  $ hg outgoing -R empty1 $remote
+  comparing with http://localhost:$HGPORT/
+  no changes found
+  [1]
+  $ hg pull -R empty1 $remote
+  pulling from http://localhost:$HGPORT/
+  no changes found
+  $ hg push -R empty1 $remote
+  pushing to http://localhost:$HGPORT/
+  no changes found
+  $ stop
+
+Base repo:
+
+  $ hg init main
+  $ cd main
+  $ hg debugbuilddag -mo '+2:tbase @name1 +3:thead1 <tbase @name2 +4:thead2 @both /thead1 +2:tmaintip'
+  $ hg glog
+  o  11 a19bfa7e7328: r11 both
+  |
+  o  10 8b6bad1512e1: r10 both
+  |
+  o    9 025829e08038: r9 both
+  |\
+  | o  8 d8f638ac69e9: r8 name2
+  | |
+  | o  7 b6b4d315a2ac: r7 name2
+  | |
+  | o  6 6c6f5d5f3c11: r6 name2
+  | |
+  | o  5 70314b29987d: r5 name2
+  | |
+  o |  4 e71dbbc70e03: r4 name1
+  | |
+  o |  3 2c8d5d5ec612: r3 name1
+  | |
+  o |  2 a7892891da29: r2 name1
+  |/
+  o  1 0019a3b924fd: r1
+  |
+  o  0 d57206cc072a: r0
+  
+  $ cd ..
+  $ start main
+
+Full clone:
+
+  $ hg clone main full
+  updating to branch default
+  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ cd full
+  $ hg incoming $remote
+  comparing with http://localhost:$HGPORT/
+  searching for changes
+  no changes found
+  [1]
+  $ hg outgoing $remote
+  comparing with http://localhost:$HGPORT/
+  searching for changes
+  no changes found
+  [1]
+  $ hg pull $remote
+  pulling from http://localhost:$HGPORT/
+  searching for changes
+  no changes found
+  $ hg push $remote
+  pushing to http://localhost:$HGPORT/
+  searching for changes
+  no changes found
+  $ cd ..
+
+Local is empty:
+
+  $ cd empty1
+  $ hg incoming $remote
+  comparing with http://localhost:$HGPORT/
+  0 d57206cc072a: r0 
+  1 0019a3b924fd: r1 
+  2 a7892891da29: r2 name1
+  3 2c8d5d5ec612: r3 name1
+  4 e71dbbc70e03: r4 name1
+  5 70314b29987d: r5 name2
+  6 6c6f5d5f3c11: r6 name2
+  7 b6b4d315a2ac: r7 name2
+  8 d8f638ac69e9: r8 name2
+  9 025829e08038: r9 both
+  10 8b6bad1512e1: r10 both
+  11 a19bfa7e7328: r11 both
+  $ hg outgoing $remote
+  comparing with http://localhost:$HGPORT/
+  no changes found
+  [1]
+  $ hg push $remote
+  pushing to http://localhost:$HGPORT/
+  no changes found
+  $ hg pull $remote
+  pulling from http://localhost:$HGPORT/
+  requesting all changes
+  adding changesets
+  adding manifests
+  adding file changes
+  added 12 changesets with 24 changes to 2 files
+  (run 'hg update' to get a working copy)
+  $ hg incoming $remote
+  comparing with http://localhost:$HGPORT/
+  searching for changes
+  no changes found
+  [1]
+  $ cd ..
+
+Local is subset:
+
+  $ hg clone main subset --rev name2 ; cd subset
+  adding changesets
+  adding manifests
+  adding file changes
+  added 6 changesets with 12 changes to 2 files
+  updating to branch name2
+  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg incoming $remote
+  comparing with http://localhost:$HGPORT/
+  searching for changes
+  6 a7892891da29: r2 name1
+  7 2c8d5d5ec612: r3 name1
+  8 e71dbbc70e03: r4 name1
+  9 025829e08038: r9 both
+  10 8b6bad1512e1: r10 both
+  11 a19bfa7e7328: r11 both
+  $ hg outgoing $remote
+  comparing with http://localhost:$HGPORT/
+  searching for changes
+  no changes found
+  [1]
+  $ hg push $remote
+  pushing to http://localhost:$HGPORT/
+  searching for changes
+  no changes found
+  $ hg pull $remote
+  pulling from http://localhost:$HGPORT/
+  searching for changes
+  adding changesets
+  adding manifests
+  adding file changes
+  added 6 changesets with 12 changes to 2 files
+  (run 'hg update' to get a working copy)
+  $ hg incoming $remote
+  comparing with http://localhost:$HGPORT/
+  searching for changes
+  no changes found
+  [1]
+  $ cd ..
+
+Remote is empty:
+
+  $ stop ; start empty2
+  $ cd main
+  $ hg incoming $remote
+  comparing with http://localhost:$HGPORT/
+  searching for changes
+  no changes found
+  [1]
+  $ hg outgoing $remote
+  comparing with http://localhost:$HGPORT/
+  searching for changes
+  0 d57206cc072a: r0 
+  1 0019a3b924fd: r1 
+  2 a7892891da29: r2 name1
+  3 2c8d5d5ec612: r3 name1
+  4 e71dbbc70e03: r4 name1
+  5 70314b29987d: r5 name2
+  6 6c6f5d5f3c11: r6 name2
+  7 b6b4d315a2ac: r7 name2
+  8 d8f638ac69e9: r8 name2
+  9 025829e08038: r9 both
+  10 8b6bad1512e1: r10 both
+  11 a19bfa7e7328: r11 both
+  $ hg pull $remote
+  pulling from http://localhost:$HGPORT/
+  searching for changes
+  no changes found
+  $ hg push $remote
+  pushing to http://localhost:$HGPORT/
+  searching for changes
+  remote: adding changesets
+  remote: adding manifests
+  remote: adding file changes
+  remote: added 12 changesets with 24 changes to 2 files
+  $ hg outgoing $remote
+  comparing with http://localhost:$HGPORT/
+  searching for changes
+  no changes found
+  [1]
+  $ cd ..
+
+Local is superset:
+
+  $ stop
+  $ hg clone main subset2 --rev name2
+  adding changesets
+  adding manifests
+  adding file changes
+  added 6 changesets with 12 changes to 2 files
+  updating to branch name2
+  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ start subset2
+  $ cd main
+  $ hg incoming $remote
+  comparing with http://localhost:$HGPORT/
+  searching for changes
+  no changes found
+  [1]
+  $ hg outgoing $remote
+  comparing with http://localhost:$HGPORT/
+  searching for changes
+  2 a7892891da29: r2 name1
+  3 2c8d5d5ec612: r3 name1
+  4 e71dbbc70e03: r4 name1
+  9 025829e08038: r9 both
+  10 8b6bad1512e1: r10 both
+  11 a19bfa7e7328: r11 both
+  $ hg pull $remote
+  pulling from http://localhost:$HGPORT/
+  searching for changes
+  no changes found
+  $ hg push $remote
+  pushing to http://localhost:$HGPORT/
+  searching for changes
+  abort: push creates new remote branches: both, name1!
+  (use 'hg push --new-branch' to create new remote branches)
+  [255]
+  $ hg push $remote --new-branch
+  pushing to http://localhost:$HGPORT/
+  searching for changes
+  remote: adding changesets
+  remote: adding manifests
+  remote: adding file changes
+  remote: added 6 changesets with 12 changes to 2 files
+  $ hg outgoing $remote
+  comparing with http://localhost:$HGPORT/
+  searching for changes
+  no changes found
+  [1]
+  $ cd ..
+
+  $ stop
+

mercurial/treediscovery.py

@@ -33,7 +33,7 b' def findcommonincoming(repo, remote, hea'
         base.add(nullid)
         if heads != [nullid]:
             return [nullid], [nullid], list(heads)
-        return [nullid], [], []
+        return [nullid], [], heads
 
     # assume we're closer to the tip than the root
     # and start by examining the heads
@@ -46,10 +46,10 b' def findcommonincoming(repo, remote, hea'
         else:
             base.add(h)
 
+    if not unknown:
+        return list(base), [], list(heads)
+
     heads = unknown
-    if not unknown:
-        return list(base), [], []
-
     req = set(unknown)
     reqcnt = 0