run-tests: work around the Windows firewall popup for server processes
Windows doesn't have a `python3` executable, so
cc0b332ab9fc attempted to work
around the issue by copying the current python to `python3.exe`. That put it in
`_tmpbindir` because of failures in `test-run-tests.t` when using `_bindir`,
which looked like a process was trying to open it to write out a copy while it
was in use. (Interestingly, I couldn't reproduce this running the test by
itself in a loop for a couple of hours, but it happens constantly when running
all tests.) The problem with using `_tmpbindir` is that it is the randomly
generated path for the test run, and instead of Windows Firewall remembering the
executable signature or image hash when allowing the process to open a server
port, it apparently remembers the image path. That means every run will trigger
a popup to allow it, which is bad for firing off a test run and walking away.
I tried to symlink to the python executable, but that currently requires admin
priviledges[1]. This will prompt the first time if the underlying python binary
has never opened a server port, but appears to avoid it on subsequent runs.
[1] https://bugs.python.org/
issue40687
Differential Revision: https://phab.mercurial-scm.org/D9815
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