I've pushed a bunch of changes and would be shocked if I got them all right, @jgraham please review for things that our CI don't actually test that need manual confirmation.

The remaining problem now is this:

py36-mypy3 create: /home/test/web-platform-tests/tools/.tox/py36-mypy3
py36-mypy3 installdeps: -rrequirements_mypy.txt
py36-mypy3 installed: mypy==0.812,mypy-extensions==0.4.3,typed-ast==1.4.3,typing-extensions==3.7.4.3
py36-mypy3 run-test-pre: PYTHONHASHSEED='1082800144'
py36-mypy3 run-test: commands[0] | mypy --config-file=/home/test/web-platform-tests/tools/mypy.ini --no-incremental -p tools.manifest -p tools.lint -p tools.gitignore
tools/lint/lint.py:847: error: "object" has no attribute "__enter__"
tools/lint/lint.py:847: error: "object" has no attribute "__exit__"
Found 2 errors in 1 file (checked 32 source files)

I'm having trouble running this locally and don't know how to fix this.

The remaining problem now is this:

py36-mypy3 create: /home/test/web-platform-tests/tools/.tox/py36-mypy3
py36-mypy3 installdeps: -rrequirements_mypy.txt
py36-mypy3 installed: mypy==0.812,mypy-extensions==0.4.3,typed-ast==1.4.3,typing-extensions==3.7.4.3
py36-mypy3 run-test-pre: PYTHONHASHSEED='1082800144'
py36-mypy3 run-test: commands[0] | mypy --config-file=/home/test/web-platform-tests/tools/mypy.ini --no-incremental -p tools.manifest -p tools.lint -p tools.gitignore
tools/lint/lint.py:847: error: "object" has no attribute "__enter__"
tools/lint/lint.py:847: error: "object" has no attribute "__exit__"
Found 2 errors in 1 file (checked 32 source files)

I'm having trouble running this locally and don't know how to fix this.

In theory cd tools; tox -e py36-mypy. The problem is that the nullcontext implementation for Python3.6 isn't recognised as a ContextManager. I tried fixing this locally but it didn't work well. Maybe @gsnedders has an idea.

I have tried tox -e py36-mypy on a machine with a python3.6 binary, but to no avail.

Since both flake8 and mypy are linters of sorts, is there really any point in ensuring they also work with 3.6, or should we just stop running them and ignore the problem?

Well in theory running mypy with 3.6 reduces the chance we end up with 3.6 specific breakage in a case where we don't have other test coverage. So I'm somewhat in favour of keeping that on (I perhaps care less about flake8, but could be convinced it's worth the small cost). In this case if we don't have a better solution we can always add type: ignore to the line with the error, although that also reduces our type coverage in later Python versions, which isn't ideal.

Yeah, since mypy is clever enough to understand the sys.version_info >= (3, 7) condition, there does seem to be some value in running it on 3.6. I just found https://mypy.readthedocs.io/en/stable/common_issues.html#spurious-errors-and-locally-silencing-the-checker and type: ignore seems like an option ultimately.

It's Monday!