view tests/test-issue672.t @ 49000:dd6b67d5c256 stable

rust: fix unsound `OwningDirstateMap`

As per the previous patch, `OwningDirstateMap` is unsound. Self-referential
structs are difficult to implement correctly in Rust since the compiler is
free to move structs around as much as it wants to. They are also very rarely
needed in practice, so the state-of-the-art on how they should be done within
the Rust rules is still a bit new.

The crate `ouroboros` is an attempt at providing a safe way (in the Rust sense)
of declaring self-referential structs. It is getting a lot attention and was
improved very quickly when soundness issues were found in the past: rather than
relying on our own (limited) review circle, we might as well use the de-facto
common crate to fix this problem. This will give us a much better chance of
finding issues should any new ones be discovered as well as the benefit of
fewer `unsafe` APIs of our own.

I was starting to think about how I would present a safe API to the old struct
but soon realized that the callback-based approach was already done in
`ouroboros`, along with a lot more care towards refusing incorrect structs.

In short: we don't return a mutable reference to the `DirstateMap` anymore, we
expect users of its API to pass a `FnOnce` that takes the map as an argument.
This allows our `OwningDirstateMap` to control the input and output lifetimes
of the code that modifies it to prevent such issues.

Changing to `ouroboros` meant changing every API with it, but it is relatively
low churn in the end. It correctly identified the example buggy modification of
`copy_map_insert` outlined in the previous patch as violating the borrow rules.

Differential Revision: https://phab.mercurial-scm.org/D12429

https://bz.mercurial-scm.org/672

# 0-2-4
#  \ \ \
#   1-3-5
#
# rename in #1, content change in #4.

  $ hg init

  $ touch 1
  $ touch 2
  $ hg commit -Am init  # 0
  adding 1
  adding 2

  $ hg rename 1 1a
  $ hg commit -m rename # 1

  $ hg co -C 0
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ echo unrelated >> 2
  $ hg ci -m unrelated1 # 2
  created new head

  $ hg merge --debug 1
    unmatched files in other:
     1a
    all copies found (* = to merge, ! = divergent, % = renamed and deleted):
     on remote side:
      src: '1' -> dst: '1a' 
    checking for directory renames
  resolving manifests
   branchmerge: True, force: False, partial: False
   ancestor: 81f4b099af3d, local: c64f439569a9+, remote: c12dcd37c90a
   1: other deleted -> r
  removing 1
   1a: remote created -> g
  getting 1a
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ hg ci -m merge1 # 3

  $ hg co -C 2
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ echo hello >> 1
  $ hg ci -m unrelated2 # 4
  created new head

  $ hg co -C 3
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ hg merge -y --debug 4
    unmatched files in local:
     1a
    all copies found (* = to merge, ! = divergent, % = renamed and deleted):
     on local side:
      src: '1' -> dst: '1a' *
    checking for directory renames
  resolving manifests
   branchmerge: True, force: False, partial: False
   ancestor: c64f439569a9, local: f4a9cff3cd0b+, remote: 746e9549ea96
  starting 4 threads for background file closing (?)
   preserving 1a for resolve of 1a
   1a: local copied/moved from 1 -> m
  picked tool ':merge' for 1a (binary False symlink False changedelete False)
  merging 1a and 1 to 1a
  my 1a@f4a9cff3cd0b+ other 1@746e9549ea96 ancestor 1@c64f439569a9
   premerge successful
  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ hg co -C 4
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ hg merge -y --debug 3
    unmatched files in other:
     1a
    all copies found (* = to merge, ! = divergent, % = renamed and deleted):
     on remote side:
      src: '1' -> dst: '1a' *
    checking for directory renames
  resolving manifests
   branchmerge: True, force: False, partial: False
   ancestor: c64f439569a9, local: 746e9549ea96+, remote: f4a9cff3cd0b
  starting 4 threads for background file closing (?)
   preserving 1 for resolve of 1a
  removing 1
   1a: remote moved from 1 -> m
  picked tool ':merge' for 1a (binary False symlink False changedelete False)
  merging 1 and 1a to 1a
  my 1a@746e9549ea96+ other 1a@f4a9cff3cd0b ancestor 1@c64f439569a9
   premerge successful
  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)