Failure in doctest CI (in a full source build) because it can't find python3 during mbedtls tests

[ViralBShah]

After the Sparse stdlibs bump PR was merged into master, the doctest CI failed because it seems to be running certain steps that don't otherwise seem to run in other PRs. It seems to need python3.

https://build.julialang.org/#/builders/54/builds/6896/steps/12/logs/stdio

checking for size_t... -- Performing Test C_COMPILER_SUPPORTS_WFORMAT_SIGNEDNESS - Success
/usr/bin/env: python3: No such file or directory
CMake Error at tests/CMakeLists.txt:21 (message):
  Cannot build test suites without Python 3
-- Configuring incomplete, errors occurred!
See also "/buildworker/worker/doctest_linux64/build/deps/scratch/mbedtls-2.28.0/CMakeFiles/CMakeOutput.log".
make[2]: *** [scratch/mbedtls-2.28.0/build-configured] Error 1
make[2]: *** Waiting for unfinished jobs....

The operation being performed is full-source-dist and it seems to have issues with Makefile dependencies as well:

make JULIA_PRECOMPILE=0 USE_BINARYBUILDER=0 full-source-dist

@DilumAluthge @staticfloat May either of you know what is up?

[inkydragon]

It looks like the test requires python3.

if(NOT MBEDTLS_PYTHON_EXECUTABLE)
    message(FATAL_ERROR "Cannot build test suites without Python 3")
endif()

https://github.com/Mbed-TLS/mbedtls/blob/8b3f26a5ac38d4fdccbc5c5366229f3e01dafcc0/tests/CMakeLists.txt#L20-L22

Python 3.6 to generate the test code, and to generate sample programs in the development branch.

—— Tool versions | Mbed-TLS/mbedtls

So just don't build test:

-DENABLE_TESTING=OFF

https://github.com/JuliaLang/julia/pull/45712/files#diff-137328a9cba83316ac89a90f305a629a1a7c585e49604af0222c54504fdb825fR9

[ViralBShah]

The build dependencies in full source build were broken because of LBT. That is fixed in #45746

[vtjnash]

I was told this runs on buildkite now, but it hasn’t gotten turned off yet here. Been broken for awhile though

[inkydragon]

Not sure which commit fixed it, but now doctest can be built successfully.
https://build.julialang.org/#/builders/54

[ViralBShah]

The doctest was not broken per se- it was only an issue in the full source build.

[ViralBShah]

@DilumAluthge Do you know if this is still an issue?

[DilumAluthge]

The issue here is about the make full-source-dist step, right? If so, then this issue is not yet resolved, because we actually lost that CI job in the Buildkite transition, and we need to add it back.

Cross-ref JuliaCI/julia-buildkite#190

[DilumAluthge]

So we should probably keep this issue open until JuliaCI/julia-buildkite#190 is fixed, and then we can double-check that this issue is fixed.

[KristofferC]

Having doctests fail in a special build seems very far from being a release blocker.

[ViralBShah]

I believe this was on regular CI that tests is the full source build works, not something special I was doing.

But it runs separately I think, once a day or something.