procutil: move comment closer to relevant code

procutil: use mercurial.windows.winstdout only on Python 2 and TTYs Python 3 already works around the bug. The workaround is only needed when writing to consoles. If stdout is a console, sys.stdout.isatty() is true.

procutil: split if condition This prepares the code for subsequent changes where we need to differentiate between the two cases.

procutil: explain better why line buffering is not possible The sentence “On Python 3, buffered binary streams can't be set line-buffered.” was imprecise, as all streams are just Python classes and we can implement our own (which we did).

tests: make subprocess handling reusable for different tests in test-stdio.py

procutil: back out 8403cc54bc83 (make ....procutil.stderr unbuffered) Changeset 8403cc54bc83 introduced code that opens a second file object referring to the stderr file descriptor. This broke tests on Windows. The reason is that on Windows, sys.stderr is buffered and procutil.stderr closed the file descriptor when it got garbage collected before sys.stderr had the chance to flush buffered data. `procutil.stdout` had the same problem for a long time, but we didn’t realize, as in CI test runs, stdout is not a TTY and in this case no second file object is opened.

test-clone-uncompressed: use config to silence the lock warning The ui.timeout.warn option can solve the issue6237 in a cleaner way than what was done in 752da6863e39. That way, possible other unexpected error output will not be silenced. Differential Revision: https://phab.mercurial-scm.org/D8726

hooklib: fix detection of successors for changeset_obsoleted Provide a hook for obsutil.getobsolete to be used with either a transaction or the changes item of the transaction, since hooks only have access to the latter. Use that to find the correct list of revisions with obsmarkers, even new ones, and then filter out revisions with known successors. Move the processing from pretxnclose to txnclose as the transaction access itself is no longer necessary. This is more in line with notify and ensures that sanity checks can abort the transaction first. Differential Revision: https://phab.mercurial-scm.org/D8575

fix: prefetch file contents This prevents the worker subprocesses from contacting the server individually, which is either inefficient, or leads to problems if the connection is shared among them. Differential Revision: https://phab.mercurial-scm.org/D8723

fix: obtain base paths before starting workers This moves calculation of base paths to before work is dispatched. While this does mean that copy tracing will be serialized instead of parallel, it is necessary to be able to prefetch the base contents in a batch, which will likely be more efficient. Differential Revision: https://phab.mercurial-scm.org/D8722