status: don't crash if a lookup file disappears
This can happen if another process (even another hg process!) comes along and
removes the file at that time.
This partly resolves issue5584, but not completely -- a bogus dirstate update
can still happen. However, the full fix is too involved for stable.
Testing that hghave does not crash when checking features
$ hghave --test-features 2>/dev/null
Testing hghave extensibility for third party tools
$ cat > hghaveaddon.py <<EOF
> import hghave
> @hghave.check("custom", "custom hghave feature")
> def has_custom():
> return True
> EOF
(invocation via run-tests.py)
$ cat > test-hghaveaddon.t <<EOF
> #require custom
> $ echo foo
> foo
> EOF
$ run-tests.py $HGTEST_RUN_TESTS_PURE test-hghaveaddon.t
.
# Ran 1 tests, 0 skipped, 0 warned, 0 failed.
(invocation via command line)
$ unset TESTDIR
$ hghave custom
(terminate with exit code 2 at failure of importing hghaveaddon.py)
$ rm hghaveaddon.*
$ cat > hghaveaddon.py <<EOF
> importing this file should cause syntax error
> EOF
$ hghave custom
failed to import hghaveaddon.py from '.': invalid syntax (hghaveaddon.py, line 1)
[2]