a848cde3

By: Tom Sydney Kerckhove <syd@cs-syd.eu>

Respect the cores nix gave the build

A test suite compiled with -N asks the RTS for every core of the machine
it runs on, which inside a nix build is not what the build was given.
Nix's cores setting reaches a build only as NIX_BUILD_CORES, so read
that, and let it decide how parallel to run when nothing else does.
Nix's --max-jobs is not visible to a build at all, so there is nothing
to respect there.

It narrows only the ByCapabilities case. Anything configured explicitly
still decides: --jobs, --synchronous, SYDTEST_JOBS, threads in the
config file, and --debug all win, so an ambient variable cannot override
a config file. The narrowing also happens after the warning about
compiling with -N is decided, so a suite stuck on one capability is
still told to add it rather than silently running n-way on one core.

Zero threads now means every capability rather than an asynchronous
runner with no workers. --jobs 0 left nothing to take tests off the
queue and the suite died with "thread blocked indefinitely in an STM
transaction". Nix documents 0 as "use every core", and the mutation
driver's own job counts have always treated it that way, so every route
into a thread count now agrees.

Total

2m35s

Created 2 days ago Started 2 days ago Finished 2 days ago

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