ui: add special-purpose atexit functionality
In spite of its longstanding use, Python's built-in atexit code is
not suitable for Mercurial's purposes, for several reasons:
* Handlers run after application code has finished.
* Because of this, the code that runs handlers swallows exceptions
(since there's no possible stacktrace to associate errors with).
If we're lucky, we'll get something spat out to stderr (if stderr
still works), which of course isn't any use in a big deployment
where it's important that exceptions get logged and aggregated.
* Mercurial's current atexit handlers make unfortunate assumptions
about process state (specifically stdio) that, coupled with the
above problems, make it impossible to deal with certain categories
of error (try "hg status > /dev/full" on a Linux box).
* In Python 3, the atexit implementation is completely hidden, so
we can't hijack the platform's atexit code to run handlers at a
time of our choosing.
As a result, here's a perfectly cromulent atexit-like implementation
over which we have control. This lets us decide exactly when the
handlers run (after each request has completed), and control what
the process state is when that occurs (and afterwards).
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init a
$ cd a
$ echo a > a
$ hg ci -Ama
adding a
$ hg qnew a.patch
$ echo a >> a
$ hg qrefresh
$ hg qnew b.patch
$ echo b > b
$ hg add b
$ hg qrefresh
$ hg qnew c.patch
$ echo c > c
$ hg add c
$ hg qrefresh
$ hg qgoto a.patch
popping c.patch
popping b.patch
now at: a.patch
$ hg qgoto c.patch
applying b.patch
applying c.patch
now at: c.patch
$ hg qgoto b.patch
popping c.patch
now at: b.patch
Using index:
$ hg qgoto 0
popping b.patch
now at: a.patch
$ hg qgoto 2
applying b.patch
applying c.patch
now at: c.patch
No warnings when using index ... and update from non-qtip and with pending
changes in unrelated files:
$ hg qnew bug314159
$ echo d >> c
$ hg qrefresh
$ hg qnew bug141421
$ echo e >> b
$ hg qrefresh
$ hg up -r bug314159
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo f >> a
$ echo f >> b
$ echo f >> c
$ hg qgoto 1
abort: local changes found, qrefresh first
[255]
$ hg qgoto 1 -f
popping bug141421
popping bug314159
popping c.patch
now at: b.patch
$ hg st
M a
M b
? c.orig
$ hg up -qCr.
$ hg qgoto 3
applying c.patch
applying bug314159
now at: bug314159
Detect ambiguous non-index:
$ hg qgoto 14
patch name "14" is ambiguous:
bug314159
bug141421
abort: patch 14 not in series
[255]
$ cd ..