patch: refactor content diffing part in separate fn so extensions can wrap
Right now extdiff uses it's own logic using archival to diff two versions of
file using external diff tools. This makes the extdiff functionality
non-extensible.
This series is an attempt to refactor core patch and diff functionality so that
extdiff can wrap and reuse it. This will help us in using external diffing tools
at more places and not just extdiff command only then.
Differential Revision: https://phab.mercurial-scm.org/D8685
tests: check that procutil.std{out,err}.write() returns correct result
On Windows, we currently don’t fully test the case when the stream is connected
to a TTY, but we test the child process side by connecting them to NUL, which
is recognized as a TTY by Python. To make the large write test a bit more
useful besides checking that it doesn’t crash, we can check that the write()
method returns the correct result.
tests: add tests for when stdout or stderr is connected to `os.devnull`
The original motivation was that creating PTYs on Windows is not possible, but
`NUL` is recognized as a TTY, so we can have at least some test coverage for
the TTY case. I think it doesn’t hurt to run the test cases on all systems.
procutil: ensure that procutil.std{out,err}.write() writes all bytes
Python 3 offers different kind of streams and it’s not guaranteed for all of
them that calling write() writes all bytes.
When Python is started in unbuffered mode, sys.std{out,err}.buffer are
instances of io.FileIO, whose write() can write less bytes for
platform-specific reasons (e.g. Linux has a 0x
7ffff000 bytes maximum and could
write less if interrupted by a signal; when writing to Windows consoles, it’s
limited to 32767 bytes to avoid the "not enough space" error). This can lead to
silent loss of data, both when using sys.std{out,err}.buffer (which may in fact
not be a buffered stream) and when using the text streams sys.std{out,err}
(I’ve created a CPython bug report for that:
https://bugs.python.org/
issue41221).
Python may fix the problem at some point. For now, we implement our own wrapper
for procutil.std{out,err} that calls the raw stream’s write() method until all
bytes have been written. We don’t use sys.std{out,err} for larger writes, so I
think it’s not worth the effort to patch them.
procutil: move assignments
This should probably be part of the previous patch, but folding it results in a
less useful word diff, so I decided to keep it separate for review.