tests/test-fix-metadata.t

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

A python hook for "hg fix" that prints out the number of files and revisions
that were affected, along with which fixer tools were applied. Also checks how
many times it sees a specific key generated by one of the fixer tools defined
below.

  $ cat >> $TESTTMP/postfixhook.py <<EOF
  > import collections
  > def file(ui, repo, rev=None, path=b'', metadata=None, **kwargs):
  >   ui.status(b'fixed %s in revision %d using %s\n' %
  >             (path, rev, b', '.join(metadata.keys())))
  > def summarize(ui, repo, replacements=None, wdirwritten=False,
  >               metadata=None, **kwargs):
  >     counts = collections.defaultdict(int)
  >     keys = 0
  >     for fixername, metadatalist in metadata.items():
  >         for metadata in metadatalist:
  >             if metadata is None:
  >                 continue
  >             counts[fixername] += 1
  >             if 'key' in metadata:
  >                 keys += 1
  >     ui.status(b'saw "key" %d times\n' % (keys,))
  >     for name, count in sorted(counts.items()):
  >         ui.status(b'fixed %d files with %s\n' % (count, name))
  >     if replacements:
  >         ui.status(b'fixed %d revisions\n' % (len(replacements),))
  >     if wdirwritten:
  >         ui.status(b'fixed the working copy\n')
  > EOF

Some mock output for fixer tools that demonstrate what could go wrong with
expecting the metadata output format.

  $ printf 'new content\n' > $TESTTMP/missing
  $ printf 'not valid json\0new content\n' > $TESTTMP/invalid
  $ printf '{"key": "value"}\0new content\n' > $TESTTMP/valid

Configure some fixer tools based on the output defined above, and enable the
hooks defined above. Disable parallelism to make output of the parallel file
processing phase stable.

  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > fix =
  > [fix]
  > metadatafalse:command=cat $TESTTMP/missing
  > metadatafalse:pattern=metadatafalse
  > metadatafalse:metadata=false
  > missing:command=cat $TESTTMP/missing
  > missing:pattern=missing
  > missing:metadata=true
  > invalid:command=cat $TESTTMP/invalid
  > invalid:pattern=invalid
  > invalid:metadata=true
  > valid:command=cat $TESTTMP/valid
  > valid:pattern=valid
  > valid:metadata=true
  > [hooks]
  > postfixfile = python:$TESTTMP/postfixhook.py:file
  > postfix = python:$TESTTMP/postfixhook.py:summarize
  > [worker]
  > enabled=false
  > EOF

See what happens when we execute each of the fixer tools. Some print warnings,
some write back to the file.

  $ hg init repo
  $ cd repo

  $ printf "old content\n" > metadatafalse
  $ printf "old content\n" > invalid
  $ printf "old content\n" > missing
  $ printf "old content\n" > valid
  $ hg add -q

  $ hg fix -w
  ignored invalid output from fixer tool: invalid
  fixed metadatafalse in revision 2147483647 using metadatafalse
  ignored invalid output from fixer tool: missing
  fixed valid in revision 2147483647 using valid
  saw "key" 1 times
  fixed 1 files with valid
  fixed the working copy

  $ cat metadatafalse
  new content
  $ cat missing
  old content
  $ cat invalid
  old content
  $ cat valid
  new content

  $ cd ..