CI only tests one OpenSSL version, but Python supports multiple versions of OpenSSL. OpenSSL 1.0.2, 1.1.0, 1.1.1, and 3.0.0 have different APIs and behave differently. We should run minimal tests with all major OpenSSL versions to ensure that Python compiles and works with supported versions.

This will slow down CI a bit. I figured out how to include ccache to speed up compilation a lot. With populated ccache configure + make takes less than 30 seconds instead of 90 seconds.

I also noticed that GHA action configuration compiles Python with custom OpenSSL but fails to set rpath / LD_LIBRARY_PATH. I think this means that we compile with custom OpenSSL but actual tests use OSS' OpenSSL libraries.

Github selects required actions based on the "name" attribute of a job. Therefore I decided to keep the default "Ubuntu" job and moved the additional OpenSSL tests to another job.

For future reference, my first approach was:

    strategy:
      fail-fast: false
      matrix:
        openssl_ver: [1.1.1k, 1.0.2u, 1.1.0l, 3.0.0-alpha14]
        include:
        - openssl_ver: 1.1.1k
          testmode: 'full'
    ...
    - name: Tests
      run: xvfb-run make buildbottest TESTOPTS="-j4 -uall,-cpu"
      if: ${{ matrix.testmode == 'full' }}
    - name: SSL tests
      run: ./python Lib/test/ssltests.py
      if: ${{ matrix.testmode != 'full' }}

The new checks are only executed when one or more OpenSSL-related files are modified. The checks run a handful of networking and hashing test suites. All SSL checks are optional. This PR also introduces ccache to speed up compilation. In common cases it speeds up configure and compile time from about 90 seconds to less than 30 seconds.

New changeset 8fa1489365e7af8b90286c97db55a2dc60a05cde by Christian Heimes in branch 'master':
bpo-43811: Test multiple OpenSSL versions on GHA (GH-25360)
https://github.com/python/cpython/commit/8fa1489365e7af8b90286c97db55a2dc60a05cde

New changeset 5ce227f3a767e6e44e7c41e0c845a83cf7777ca4 by Miss Islington (bot) in branch '3.9':
[3.9] bpo-43811: Test multiple OpenSSL versions on GHA (GH-25360) (GH-25391)
https://github.com/python/cpython/commit/5ce227f3a767e6e44e7c41e0c845a83cf7777ca4

New changeset a607815eb07582deb3c5818be881a98abe25a100 by Miss Islington (bot) in branch '3.8':
[3.8] bpo-43811: Test multiple OpenSSL versions on GHA (GH-25360) (GH-25392)
https://github.com/python/cpython/commit/a607815eb07582deb3c5818be881a98abe25a100