discovery: avoid wrongly saying there are nothing to pull

We can get in a situation where a revision passed through `hg pull --rev REV`
are available on the server, but not a descendant of the advertised server
heads.

For example the server could lying be during heads advertisement, to hide some
pull request. Or obsolete/hidden content could be explicitly pulled.

So in this case the lookup associated to `REV` returned successfully, but the
normal discovery will find all advertised heads already known locally. This flip
a special boolean `anyinc` that will prevent any fetch attempt, preventing `REV`
to be pulled over.

We add three line of code to detect this case and make sure a pull actually
happens.

My main target is to make some third party extensions happy (I expect the
associated test to move upstream with the extension). However this fix already
make some of the `infinitepush` test happier.

mercurial/discovery.py

@@ -67,6 +67,10 b' def findcommonincoming(repo, remote, hea'
         ancestorsof=ancestorsof,
     )
     common, anyinc, srvheads = res
+    if heads and not anyinc:
+        # server could be lying on the advertised heads
+        has_node = repo.changelog.hasnode
+        anyinc = any(not has_node(n) for n in heads)
     return (list(common), anyinc, heads or list(srvheads))
 
 

tests/test-infinitepush-ci.t

@@ -249,12 +249,12 b' XXX: we should show better message when '
   $ hg pull -r b4e4bce660512ad3e71189e14588a70ac8e31fef
   pulling from ssh://user@dummy/repo
   searching for changes
-  no changes found
   adding changesets
   adding manifests
   adding file changes
   added 4 changesets with 4 changes to 4 files
   new changesets eaba929e866c:b4e4bce66051
+  (run 'hg update' to get a working copy)
   $ hg glog
   o  5:b4e4bce66051 added e
   |  public