mypy Enable warn_unreachable = True for `mypyc` and all other files as well

Achieves a todo, enabling warn_unreachable = True for mypyc and all other files as well

May 08 '25 02:05 wyattscarpenter

I am now waiting on https://github.com/mypyc/mypyc/issues/1101 to be resolved to finish this issue, after which I will have to rebase this branch onto master to get the resolution.

May 08 '25 02:05 wyattscarpenter

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅

May 08 '25 03:05 github-actions[bot]

Wow, only one hit? That should be easy to resolve...

May 09 '25 16:05 sterliakov

@stanislavlevin, yep! Only one hit for this project 🥳! Unfortunately (so to speak), deciding what to do about that is best left to people more familiar with mypyc than me.

I could simply comment out this code, which I might do eventually, but if someone with a better idea about what it should do comes along, I will defer to them.

May 10 '25 02:05 wyattscarpenter

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅

Jun 07 '25 10:06 github-actions[bot]

Hmm, another hit. I guess it was masked or subsequently developed or something... Running the self-check on my computer, with python 3.9, doesn't produce this problem, even with --python-version 3.9 🤔. So I guess it's an actual python language behavior change...

Jun 07 '25 13:06 wyattscarpenter

Even after installing python 3.9 I can't reproduce this. Odd.

I'll try merging again once another commit hits master, in case this was a fluke.

Jun 07 '25 13:06 wyattscarpenter

Even after installing python 3.9 I can't reproduce this. Odd.

FWIW, I can reproduce this locally in a fresh 3.9 venv:

$ python --version
Python 3.9.23
$ python -m mypy --config-file mypy_self_check.ini misc --exclude misc/sync-typeshed.py
misc/analyze_cache.py:44: error: Statement is unreachable  [unreachable]
                elif isinstance(chunk, list):
                ^
misc/analyze_cache.py:44: note: See https://mypy.rtfd.io/en/stable/_refs.html#code-unreachable for more info
misc/analyze_cache.py:96: error: Statement is unreachable  [unreachable]
                return chunk
                ^~~~~~~~~~~~
misc/analyze_cache.py:127: error: Statement is unreachable  [unreachable]
                return chunk
                ^~~~~~~~~~~~
Found 3 errors in 1 file (checked 17 source files)

I'll try merging again once another commit hits master, in case this was a fluke.

quick git tip: you can also tickle the CI by pushing an empty commit with git commit --allow-empty

Jun 09 '25 19:06 brianschubert

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅

Jun 09 '25 19:06 github-actions[bot]

Well, now time has passed and we're down to one different problem, apparently:

mypyc/test/test_cheader.py:35: error: Subclass of "list[PrimitiveDescription]" and "PrimitiveDescription" cannot exist: "PrimitiveDescription" is final  [unreachable]
                    if isinstance(ops, PrimitiveDescription):
                                  ^~~
mypyc/test/test_cheader.py:35: note: See https://mypy.rtfd.io/en/stable/_refs.html#code-unreachable for more info
mypyc/test/test_cheader.py:36: error: Statement is unreachable  [unreachable]
                        ops = [ops]
                        ^~~~~~~~~~~
Found 2 errors in 1 file (checked 313 source files)

Aug 14 '25 22:08 wyattscarpenter

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅

Aug 14 '25 22:08 github-actions[bot]

if isinstance(ops, PrimitiveDescription):

This and the following line can probably be removed, since the isinstance check can never be true.

Aug 15 '25 11:08 JukkaL

Let's remove that and try to merge this before we introduce another unreachable block:)

Aug 15 '25 13:08 sterliakov

The unreachable code is now removed on master.

Aug 15 '25 14:08 JukkaL

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅

Aug 15 '25 18:08 github-actions[bot]

Ok, well, now it's back to the isinstance(chunk, list) unreachable error from before.

(Edit: assuming this doesn't clear up on its own by the next time I look into it, I'll probably just throw in a couple type-ignores with TODOs next to them. Better than not having this analysis run at all...)

Aug 15 '25 18:08 wyattscarpenter