rhg: Propagate permission errors when finding a repository
The Rust standard library has a `Path::is_dir` method that returns false
for any I/O error (such as a permission error),
not just "No such file or directory".
Instead add an `is_dir` function that returns false for non-directories
and for "No such file or directory" errors, but propagates other I/O errors.
Differential Revision: https://phab.mercurial-scm.org/D11230
#require no-windows
$ . "$TESTDIR/remotefilelog-library.sh"
$ hg init master
$ cd master
$ cat >> .hg/hgrc <<EOF
> [remotefilelog]
> server=True
> EOF
$ echo x > x
$ hg commit -qAm x
$ echo y >> x
$ hg commit -qAm y
$ echo z >> x
$ hg commit -qAm z
$ hg update 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo w >> x
$ hg commit -qAm w
$ cd ..
Shallow clone and activate getflogheads testing extension
$ hgcloneshallow ssh://user@dummy/master shallow --noupdate
streaming all changes
2 files to transfer, 908 bytes of data
transferred 908 bytes in * seconds (*/sec) (glob)
searching for changes
no changes found
$ cd shallow
$ cat >> .hg/hgrc <<EOF
> [extensions]
> getflogheads=$TESTDIR/remotefilelog-getflogheads.py
> EOF
Get heads of a remotefilelog
$ hg getflogheads x
2797809ca5e9c2f307d82b1345e832f655fb99a2
ca758b402ddc91e37e3113e1a97791b537e1b7bb
Get heads of a non-existing remotefilelog
$ hg getflogheads y
EMPTY