tests/test-rebase-interruptions.t

cborutil: implement sans I/O decoder

The vendored CBOR package decodes by calling read(n) on an object.
There are a number of disadvantages to this:

* Uses blocking I/O. If sufficient data is not available, the decoder
  will hang until it is.
* No support for partial reads. If the read(n) returns less data than
  requested, the decoder raises an error.
* Requires the use of a file like object. If the original data is in
  say a buffer, we need to "cast" it to e.g. a BytesIO to appease the
  decoder.

In addition, the vendored CBOR decoder doesn't provide flexibility
that we desire. Specifically:

* It buffers indefinite length bytestrings instead of streaming them.
* It doesn't allow limiting the set of types that can be decoded. This
  property is useful when implementing a "hardened" decoder that is
  less susceptible to abusive input.
* It doesn't provide sufficient "hook points" and introspection to
  institute checks around behavior. These are useful for implementing
  a "hardened" decoder.

This all adds up to a reasonable set of justifications for writing our
own decoder.

So, this commit implements our own CBOR decoder.

At the heart of the decoder is a function that decodes a single "item"
from a buffer. This item can be a complete simple value or a special
value, such as "start of array." Using this function, we can build a
decoder that effectively iterates over the stream of decoded items and
builds up higher-level values, such as arrays, maps, sets, and indefinite
length bytestrings. And we can do this without performing I/O in the
decoder itself.

The core of the sans I/O decoder will probably not be used directly.
Instead, it is expected that we'll build utility functions for invoking
the decoder given specific input types. This will allow extreme
flexibility in how data is delivered to the decoder.

I'm pretty happy with the state of the decoder modulo the TODO items
to track wanted features to help with a "hardened" decoder. The one
thing I could be convinced to change is the handling of semantic tags.
Since we only support a single semantic tag (sets), I thought it would
be easier to handle them inline in decodeitem(). This is simpler now.
But if we add support for other semantic tags, it will likely be easier
to move semantic tag handling outside of decodeitem(). But, properly
supporting semantic tags opens up a whole can of worms, as many
semantic tags imply new types. I'm optimistic we won't need these in
Mercurial. But who knows.

I'm also pretty happy with the test coverage. Writing comprehensive
tests for partial decoding did flush out a handful of bugs. One
general improvement to testing would be fuzz testing for partial
decoding. I may implement that later. I also anticipate switching the
wire protocol code to this new decoder will flush out any lingering
bugs.

Differential Revision: https://phab.mercurial-scm.org/D4414

  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > rebase=
  > 
  > [phases]
  > publish=False
  > 
  > [alias]
  > tglog = log -G --template "{rev}: {node|short} '{desc}' {branches}\n"
  > tglogp = log -G --template "{rev}: {node|short} {phase} '{desc}' {branches}\n"
  > EOF


  $ hg init a
  $ cd a

  $ echo A > A
  $ hg ci -Am A
  adding A

  $ echo B > B
  $ hg ci -Am B
  adding B

  $ echo C >> A
  $ hg ci -m C

  $ hg up -q -C 0

  $ echo D >> A
  $ hg ci -m D
  created new head

  $ echo E > E
  $ hg ci -Am E
  adding E

  $ cd ..


Changes during an interruption - continue:

  $ hg clone -q -u . a a1
  $ cd a1

  $ hg tglog
  @  4: ae36e8e3dfd7 'E'
  |
  o  3: 46b37eabc604 'D'
  |
  | o  2: 965c486023db 'C'
  | |
  | o  1: 27547f69f254 'B'
  |/
  o  0: 4a2df7238c3b 'A'
  
Rebasing B onto E:

  $ hg rebase -s 1 -d 4
  rebasing 1:27547f69f254 "B"
  rebasing 2:965c486023db "C"
  merging A
  warning: conflicts while merging A! (edit, then use 'hg resolve --mark')
  unresolved conflicts (see hg resolve, then hg rebase --continue)
  [1]

Force a commit on C during the interruption:

  $ hg up -q -C 2 --config 'extensions.rebase=!'

  $ echo 'Extra' > Extra
  $ hg add Extra
  $ hg ci -m 'Extra' --config 'extensions.rebase=!'

Force this commit onto secret phase

  $ hg phase --force --secret 6

  $ hg tglogp
  @  6: deb5d2f93d8b secret 'Extra'
  |
  | o  5: 45396c49d53b draft 'B'
  | |
  | o  4: ae36e8e3dfd7 draft 'E'
  | |
  | o  3: 46b37eabc604 draft 'D'
  | |
  o |  2: 965c486023db draft 'C'
  | |
  o |  1: 27547f69f254 draft 'B'
  |/
  o  0: 4a2df7238c3b draft 'A'
  
Resume the rebasing:

  $ hg rebase --continue
  already rebased 1:27547f69f254 "B" as 45396c49d53b
  rebasing 2:965c486023db "C"
  merging A
  warning: conflicts while merging A! (edit, then use 'hg resolve --mark')
  unresolved conflicts (see hg resolve, then hg rebase --continue)
  [1]

Solve the conflict and go on:

  $ echo 'conflict solved' > A
  $ rm A.orig
  $ hg resolve -m A
  (no more unresolved files)
  continue: hg rebase --continue

  $ hg rebase --continue
  already rebased 1:27547f69f254 "B" as 45396c49d53b
  rebasing 2:965c486023db "C"
  warning: orphaned descendants detected, not stripping 27547f69f254, 965c486023db

  $ hg tglogp
  o  7: d2d25e26288e draft 'C'
  |
  | o  6: deb5d2f93d8b secret 'Extra'
  | |
  o |  5: 45396c49d53b draft 'B'
  | |
  @ |  4: ae36e8e3dfd7 draft 'E'
  | |
  o |  3: 46b37eabc604 draft 'D'
  | |
  | o  2: 965c486023db draft 'C'
  | |
  | o  1: 27547f69f254 draft 'B'
  |/
  o  0: 4a2df7238c3b draft 'A'
  
  $ cd ..


Changes during an interruption - abort:

  $ hg clone -q -u . a a2
  $ cd a2

  $ hg tglog
  @  4: ae36e8e3dfd7 'E'
  |
  o  3: 46b37eabc604 'D'
  |
  | o  2: 965c486023db 'C'
  | |
  | o  1: 27547f69f254 'B'
  |/
  o  0: 4a2df7238c3b 'A'
  
Rebasing B onto E:

  $ hg rebase -s 1 -d 4
  rebasing 1:27547f69f254 "B"
  rebasing 2:965c486023db "C"
  merging A
  warning: conflicts while merging A! (edit, then use 'hg resolve --mark')
  unresolved conflicts (see hg resolve, then hg rebase --continue)
  [1]

Force a commit on B' during the interruption:

  $ hg up -q -C 5 --config 'extensions.rebase=!'

  $ echo 'Extra' > Extra
  $ hg add Extra
  $ hg ci -m 'Extra' --config 'extensions.rebase=!'

  $ hg tglog
  @  6: 402ee3642b59 'Extra'
  |
  o  5: 45396c49d53b 'B'
  |
  o  4: ae36e8e3dfd7 'E'
  |
  o  3: 46b37eabc604 'D'
  |
  | o  2: 965c486023db 'C'
  | |
  | o  1: 27547f69f254 'B'
  |/
  o  0: 4a2df7238c3b 'A'
  
Abort the rebasing:

  $ hg rebase --abort
  warning: new changesets detected on destination branch, can't strip
  rebase aborted

  $ hg tglog
  @  6: 402ee3642b59 'Extra'
  |
  o  5: 45396c49d53b 'B'
  |
  o  4: ae36e8e3dfd7 'E'
  |
  o  3: 46b37eabc604 'D'
  |
  | o  2: 965c486023db 'C'
  | |
  | o  1: 27547f69f254 'B'
  |/
  o  0: 4a2df7238c3b 'A'
  
  $ cd ..

Changes during an interruption - abort (again):

  $ hg clone -q -u . a a3
  $ cd a3

  $ hg tglogp
  @  4: ae36e8e3dfd7 draft 'E'
  |
  o  3: 46b37eabc604 draft 'D'
  |
  | o  2: 965c486023db draft 'C'
  | |
  | o  1: 27547f69f254 draft 'B'
  |/
  o  0: 4a2df7238c3b draft 'A'
  
Rebasing B onto E:

  $ hg rebase -s 1 -d 4
  rebasing 1:27547f69f254 "B"
  rebasing 2:965c486023db "C"
  merging A
  warning: conflicts while merging A! (edit, then use 'hg resolve --mark')
  unresolved conflicts (see hg resolve, then hg rebase --continue)
  [1]

Change phase on B and B'

  $ hg up -q -C 5 --config 'extensions.rebase=!'
  $ hg phase --public 1
  $ hg phase --public 5
  $ hg phase --secret -f 2

  $ hg tglogp
  @  5: 45396c49d53b public 'B'
  |
  o  4: ae36e8e3dfd7 public 'E'
  |
  o  3: 46b37eabc604 public 'D'
  |
  | o  2: 965c486023db secret 'C'
  | |
  | o  1: 27547f69f254 public 'B'
  |/
  o  0: 4a2df7238c3b public 'A'
  
Abort the rebasing:

  $ hg rebase --abort
  warning: can't clean up public changesets 45396c49d53b
  rebase aborted

  $ hg tglogp
  @  5: 45396c49d53b public 'B'
  |
  o  4: ae36e8e3dfd7 public 'E'
  |
  o  3: 46b37eabc604 public 'D'
  |
  | o  2: 965c486023db secret 'C'
  | |
  | o  1: 27547f69f254 public 'B'
  |/
  o  0: 4a2df7238c3b public 'A'
  
Test rebase interrupted by hooks

  $ hg up 2
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ echo F > F
  $ hg add F
  $ hg ci -m F

  $ cd ..

(precommit version)

  $ cp -R a3 hook-precommit
  $ cd hook-precommit
  $ hg rebase --source 2 --dest 5 --tool internal:other --config 'hooks.precommit=hg status | grep "M A"'
  rebasing 2:965c486023db "C"
  M A
  rebasing 6:a0b2430ebfb8 "F" (tip)
  abort: precommit hook exited with status 1
  [255]
  $ hg tglogp
  @  7: 401ccec5e39f secret 'C'
  |
  | @  6: a0b2430ebfb8 secret 'F'
  | |
  o |  5: 45396c49d53b public 'B'
  | |
  o |  4: ae36e8e3dfd7 public 'E'
  | |
  o |  3: 46b37eabc604 public 'D'
  | |
  | o  2: 965c486023db secret 'C'
  | |
  | o  1: 27547f69f254 public 'B'
  |/
  o  0: 4a2df7238c3b public 'A'
  
  $ hg rebase --continue
  already rebased 2:965c486023db "C" as 401ccec5e39f
  rebasing 6:a0b2430ebfb8 "F"
  saved backup bundle to $TESTTMP/hook-precommit/.hg/strip-backup/965c486023db-aa6250e7-rebase.hg
  $ hg tglogp
  @  6: 6e92a149ac6b secret 'F'
  |
  o  5: 401ccec5e39f secret 'C'
  |
  o  4: 45396c49d53b public 'B'
  |
  o  3: ae36e8e3dfd7 public 'E'
  |
  o  2: 46b37eabc604 public 'D'
  |
  | o  1: 27547f69f254 public 'B'
  |/
  o  0: 4a2df7238c3b public 'A'
  
  $ cd ..

(pretxncommit version)

  $ cp -R a3 hook-pretxncommit
  $ cd hook-pretxncommit
  $ hg rebase --source 2 --dest 5 --tool internal:other \
  >     --config 'hooks.tonative.pretxncommit=True' --config 'hooks.pretxncommit=hg log -r $HG_NODE | grep "summary:     C"'
  rebasing 2:965c486023db "C"
  summary:     C
  rebasing 6:a0b2430ebfb8 "F" (tip)
  transaction abort!
  rollback completed
  abort: pretxncommit hook exited with status 1
  [255]
  $ hg tglogp
  @  7: 401ccec5e39f secret 'C'
  |
  | @  6: a0b2430ebfb8 secret 'F'
  | |
  o |  5: 45396c49d53b public 'B'
  | |
  o |  4: ae36e8e3dfd7 public 'E'
  | |
  o |  3: 46b37eabc604 public 'D'
  | |
  | o  2: 965c486023db secret 'C'
  | |
  | o  1: 27547f69f254 public 'B'
  |/
  o  0: 4a2df7238c3b public 'A'
  
  $ hg rebase --continue
  already rebased 2:965c486023db "C" as 401ccec5e39f
  rebasing 6:a0b2430ebfb8 "F"
  saved backup bundle to $TESTTMP/hook-pretxncommit/.hg/strip-backup/965c486023db-aa6250e7-rebase.hg
  $ hg tglogp
  @  6: 6e92a149ac6b secret 'F'
  |
  o  5: 401ccec5e39f secret 'C'
  |
  o  4: 45396c49d53b public 'B'
  |
  o  3: ae36e8e3dfd7 public 'E'
  |
  o  2: 46b37eabc604 public 'D'
  |
  | o  1: 27547f69f254 public 'B'
  |/
  o  0: 4a2df7238c3b public 'A'
  
  $ cd ..

(pretxnclose version)

  $ cp -R a3 hook-pretxnclose
  $ cd hook-pretxnclose
  $ hg rebase --source 2 --dest 5 --tool internal:other --config 'hooks.pretxnclose=hg log -r tip | grep "summary:     C"'
  rebasing 2:965c486023db "C"
  summary:     C
  rebasing 6:a0b2430ebfb8 "F" (tip)
  transaction abort!
  rollback completed
  abort: pretxnclose hook exited with status 1
  [255]
  $ hg tglogp
  @  7: 401ccec5e39f secret 'C'
  |
  | @  6: a0b2430ebfb8 secret 'F'
  | |
  o |  5: 45396c49d53b public 'B'
  | |
  o |  4: ae36e8e3dfd7 public 'E'
  | |
  o |  3: 46b37eabc604 public 'D'
  | |
  | o  2: 965c486023db secret 'C'
  | |
  | o  1: 27547f69f254 public 'B'
  |/
  o  0: 4a2df7238c3b public 'A'
  
  $ hg rebase --continue
  already rebased 2:965c486023db "C" as 401ccec5e39f
  rebasing 6:a0b2430ebfb8 "F"
  saved backup bundle to $TESTTMP/hook-pretxnclose/.hg/strip-backup/965c486023db-aa6250e7-rebase.hg
  $ hg tglogp
  @  6: 6e92a149ac6b secret 'F'
  |
  o  5: 401ccec5e39f secret 'C'
  |
  o  4: 45396c49d53b public 'B'
  |
  o  3: ae36e8e3dfd7 public 'E'
  |
  o  2: 46b37eabc604 public 'D'
  |
  | o  1: 27547f69f254 public 'B'
  |/
  o  0: 4a2df7238c3b public 'A'
  
  $ cd ..

Make sure merge state is cleaned up after a no-op rebase merge (issue5494)
  $ hg init repo
  $ cd repo
  $ echo a > a
  $ hg commit -qAm base
  $ echo b >> a
  $ hg commit -qm b
  $ hg up '.^'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo c >> a
  $ hg commit -qm c
  $ hg rebase -s 1 -d 2 --noninteractive
  rebasing 1:fdaca8533b86 "b"
  merging a
  warning: conflicts while merging a! (edit, then use 'hg resolve --mark')
  unresolved conflicts (see hg resolve, then hg rebase --continue)
  [1]
  $ echo a > a
  $ echo c >> a
  $ hg resolve --mark a
  (no more unresolved files)
  continue: hg rebase --continue
  $ hg rebase --continue
  rebasing 1:fdaca8533b86 "b"
  note: rebase of 1:fdaca8533b86 created no changes to commit
  saved backup bundle to $TESTTMP/repo/.hg/strip-backup/fdaca8533b86-7fd70513-rebase.hg
  $ hg resolve --list
  $ test -d .hg/merge
  [1]
Now try again with --collapse
  $ hg unbundle -q .hg/strip-backup/fdaca8533b86-7fd70513-rebase.hg
  $ hg rebase -s 2 -d 1 --noninteractive --collapse
  rebasing 2:fdaca8533b86 "b" (tip)
  merging a
  warning: conflicts while merging a! (edit, then use 'hg resolve --mark')
  unresolved conflicts (see hg resolve, then hg rebase --continue)
  [1]
  $ echo a > a
  $ echo c >> a
  $ hg resolve --mark a
  (no more unresolved files)
  continue: hg rebase --continue
  $ hg rebase --continue
  rebasing 2:fdaca8533b86 "b" (tip)
  saved backup bundle to $TESTTMP/repo/.hg/strip-backup/fdaca8533b86-7fd70513-rebase.hg
  $ hg resolve --list
  $ test -d .hg/merge
  [1]