Add encoding parameter to fix CI.

[jpakkane]

The test does not actually fail, but the test runner seems to think that if anything gets printed to stderr, that is a failure.

https://nibblestew.blogspot.com/2019/04/an-important-message-for-people.html

[nirbheek]

How does adding encoding/text parameters cause the test to not output to stderr? I would've thought that stderr=subprocess.STDOUT would be the fix here.

[eli-schwartz]

Python will print internal EncodingWarning for call sites that don't use encoding='utf-8', because the CI exports an environment variable that makes it treat them as a warning.

Unfortunately python upstream has chosen to make it impossible to use an environment variable to only produce EncodingWarning for specific modules (in particular we care about this for mesonbuild.*) so we have to first trigger the warnings like this and then make them "werror" by running code in mesonmain.py using the warnings module. So it "leaks" into the test runner even though we don't actually want it to.

However, I don't either get why this would be an error. The warning would happen in process by the test runner logic but not coming from the subprocess. It is run_meson_command_tests.py that will print an encoding warning, surely. What is checking for noisy stderr there?

[nirbheek]

It's powershell on Azure CI: https://learn.microsoft.com/en-us/azure/devops/pipelines/tasks/reference/powershell-v1?view=azure-pipelines

failOnStandardError - Fail on Standard Error
boolean. Default value: true.

If the value of this boolean is true, the task fails if any errors are written to the error pipeline or if any data is written to the Standard Error stream. Otherwise, the task relies on the exit code to determine failure.

So setting that to false will fix it.

[jpakkane]

What is checking for noisy stderr there?

The testing framework itself.

[jpakkane]

So setting that to false will fix it.

This is an issue that keeps popping up. It's better to fix it properly rather than disable in build settings, because if you do the latter, this will keep reappearing in the future as test and CI frameworks change.