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
$ cat > .hg/hgrc <<EOF
> [extensions]
> prefixfilter = prefix.py
> [encode]
> *.txt = stripprefix: Copyright 2046, The Masters
> [decode]
> *.txt = insertprefix: Copyright 2046, The Masters
> EOF
$ cat > prefix.py <<EOF
> from mercurial import error
> def stripprefix(s, cmd, filename, **kwargs):
> header = b'%s\n' % cmd
> if s[:len(header)] != header:
> raise error.Abort(b'missing header "%s" in %s' % (cmd, filename))
> return s[len(header):]
> def insertprefix(s, cmd):
> return b'%s\n%s' % (cmd, s)
> def reposetup(ui, repo):
> repo.adddatafilter(b'stripprefix:', stripprefix)
> repo.adddatafilter(b'insertprefix:', insertprefix)
> EOF
$ cat > .hgignore <<EOF
> .hgignore
> prefix.py
> prefix.pyc
> __pycache__/
> EOF
$ cat > stuff.txt <<EOF
> Copyright 2046, The Masters
> Some stuff to ponder very carefully.
> EOF
$ hg add stuff.txt
$ hg ci -m stuff
Repository data:
$ hg cat stuff.txt
Some stuff to ponder very carefully.
Fresh checkout:
$ rm stuff.txt
$ hg up -C
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cat stuff.txt
Copyright 2046, The Masters
Some stuff to ponder very carefully.
$ echo "Very very carefully." >> stuff.txt
$ hg stat
M stuff.txt
$ echo "Unauthorized material subject to destruction." > morestuff.txt
Problem encoding:
$ hg add morestuff.txt
$ hg ci -m morestuff
abort: missing header "Copyright 2046, The Masters" in morestuff.txt
[255]
$ hg stat
M stuff.txt
A morestuff.txt