requires: re-use vfs.tryread for simplicity
Avoids calling `set` twice or having to re-raise an exception and implements the routine with a single return expression.
$ . "$TESTDIR/narrow-library.sh"
$ hg init master
$ cd master
$ echo treemanifest >> .hg/requires
$ echo 'contents of file' > file
$ mkdir foo
$ echo 'contents of foo/bar' > foo/bar
$ hg ci -Am 'some change'
adding file
adding foo/bar
$ cd ..
$ hg clone --narrow ssh://user@dummy/master copy --include=foo
requesting all changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
new changesets * (glob)
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd copy
$ hg debugdirstate --no-dates
n * 20 * foo/bar (glob)
$ mv .hg/dirstate .hg/old_dirstate
$ dd bs=40 count=1 if=.hg/old_dirstate of=.hg/dirstate 2>/dev/null
$ hg debugdirstate
$ hg debugrebuilddirstate
$ hg debugdirstate
n * * unset foo/bar (glob)