rust-utils: move the `filesystem_now` function to a util
This is going to be useful for an upcoming `hg update` fastpath.
test sparse
$ hg init myrepo
$ cd myrepo
$ cat >> $HGRCPATH <<EOF
> [extensions]
> sparse=
> purge=
> strip=
> rebase=
> EOF
$ echo a > index.html
$ echo x > data.py
$ echo z > readme.txt
$ cat > base.sparse <<EOF
> [include]
> *.sparse
> EOF
$ hg ci -Aqm 'initial'
$ cat > webpage.sparse <<EOF
> %include base.sparse
> [include]
> *.html
> EOF
$ hg ci -Aqm 'initial'
Clear rules when there are includes
$ hg debugsparse --include *.py
$ ls -A
.hg
data.py
$ hg debugsparse --clear-rules
$ ls -A
.hg
base.sparse
data.py
index.html
readme.txt
webpage.sparse
Clear rules when there are excludes
$ hg debugsparse -X base.sparse -X webpage.sparse
$ ls -A
.hg
data.py
index.html
readme.txt
$ hg debugsparse --clear-rules
$ ls -A
.hg
base.sparse
data.py
index.html
readme.txt
webpage.sparse
Clearing rules should not alter profiles
$ hg debugsparse --enable-profile webpage.sparse
$ ls -A
.hg
base.sparse
index.html
webpage.sparse
$ hg debugsparse --include *.py
$ ls -A
.hg
base.sparse
data.py
index.html
webpage.sparse
$ hg debugsparse --clear-rules
$ ls -A
.hg
base.sparse
index.html
webpage.sparse