dirstate-tree: Add tree traversal/iteration
Like Python’s, Rust’s iterators are "external" in that they are driven
by a caller who calls a `next` method. This is as opposed to "internal"
iterators who drive themselves and call a callback for each item.
Writing an internal iterator traversing a tree is easy with recursion,
but internal iterators cannot rely on the call stack in that way,
they must save in an explicit object all state that they need to be
preserved across two `next` calls.
This algorithm uses a `Vec` as a stack that contains what would be
local variables on the call stack if we could use recursion.
Differential Revision: https://phab.mercurial-scm.org/D10370
$ hg init
$ echo a > a
$ hg ci -Am0
adding a
$ hg -q clone . foo
$ touch .hg/store/journal
$ echo foo > a
$ hg ci -Am0
abort: abandoned transaction found
(run 'hg recover' to clean up transaction)
[255]
$ hg recover
rolling back interrupted transaction
(verify step skipped, run `hg verify` to check your repository content)
recover, explicit verify
$ touch .hg/store/journal
$ hg ci -Am0
abort: abandoned transaction found
(run 'hg recover' to clean up transaction)
[255]
$ hg recover --verify
rolling back interrupted transaction
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
checked 1 changesets with 1 changes to 1 files
recover, no verify
$ touch .hg/store/journal
$ hg ci -Am0
abort: abandoned transaction found
(run 'hg recover' to clean up transaction)
[255]
$ hg recover --no-verify
rolling back interrupted transaction
(verify step skipped, run `hg verify` to check your repository content)
Check that zero-size journals are correctly aborted:
#if unix-permissions no-root
$ hg bundle -qa repo.hg
$ chmod -w foo/.hg/store/00changelog.i
$ hg -R foo unbundle repo.hg
adding changesets
abort: Permission denied: '$TESTTMP/foo/.hg/store/.00changelog.i-*' (glob)
[255]
$ if test -f foo/.hg/store/journal; then echo 'journal exists :-('; fi
#endif