view tests/test-fix-metadata.t @ 47965:f9e6f2bb721d

rhg: Don’t compare ambiguous files one byte at a time

Even though the use of `BufReader` reduces the number of syscalls to read
the file from disk, `.bytes()` yields a separate `Result` for every byte.
Creating those results and dispatching on them is most likely costly.

Instead, this commit opts for simplicity by reading the entire file into memory
and comparing a single pair of byte strings. Note that memory already needs to
contain the entire previous contents of the file, as read from the filelog.
So with an extremely large file this doubles memory use but does not make it
grow by orders of magnitude.

At first I wrote code that still avoids reading the entire file into memory
and compares one buffer at a time with `BufReader`. Find this code below for
posterity. However its correctness is subtle. I ended up preferring the
simplicity of the obviously-correct single comparison.

```rust
let mut reader = BufReader::new(fobj);
let mut expected = &contents_in_p1[..];
loop {
    let buf = reader.fill_buf().when_reading_file(&fs_path)?;
    if buf.is_empty() {
        // Found EOF
        return Ok(expected.is_empty());
    } else if let Some(rest) = expected.drop_prefix(buf) {
        // What we read so far matches the expected content, continue reading
        let buf_len = buf.len();
        reader.consume(buf_len);
        expected = rest
    } else {
        // Found different content
        return Ok(false);
    }
}
```

Differential Revision: https://phab.mercurial-scm.org/D11412

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 ..