branchcache: add a "pure topological head" fast path
In a narrow but actually quick common case, all topological heads are all on
the same branch and all open. In this case, computing the branch map is very
simple. We can quickly detect situation where this situation will not change.
So we update the V3 format to be able to express this situation and upgrade the
update code to detect we remains in that mode.
The branch cache is populated with the actual value when the branch map is
accessed, but the update_disk method can do the update without needing to
populate it.
#require no-windows
$ . "$TESTDIR/remotefilelog-library.sh"
$ hg init master
$ cd master
$ cat >> .hg/hgrc <<EOF
> [remotefilelog]
> server=True
> EOF
$ echo x > x
$ echo y > y
$ echo z > z
$ hg commit -qAm xy
$ cd ..
$ hgcloneshallow ssh://user@dummy/master shallow -q
3 files fetched over 1 fetches - (3 misses, 0.00% hit ratio) over *s (glob)
$ cd shallow
Verify error message when noc achepath specified
$ hg up -q null
$ cp $HGRCPATH $HGRCPATH.bak
$ grep -v cachepath < $HGRCPATH.bak > tmp
$ mv tmp $HGRCPATH
$ hg up tip
abort: could not find config option remotefilelog.cachepath
[255]
$ mv $HGRCPATH.bak $HGRCPATH
Verify error message when no fallback specified
$ hg up -q null
$ rm .hg/hgrc
$ clearcache
$ hg up tip
3 files fetched over 1 fetches - (3 misses, 0.00% hit ratio) over *s (glob)
abort: no remotefilelog server configured - is your .hg/hgrc trusted?
[255]