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

[wyattscarpenter]

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

[wyattscarpenter]

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

[sterliakov]

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

[wyattscarpenter]

@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.

[wyattscarpenter]

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...

[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.

[brianschubert]

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

[wyattscarpenter]

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)

[JukkaL]

if isinstance(ops, PrimitiveDescription):

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

[sterliakov]

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

[JukkaL]

The unreachable code is now removed on master.

[wyattscarpenter]

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...)

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

AutoSplit (https://github.com/Toufool/AutoSplit)
-   File "/tmp/mypy_primer/mypy_old/venv/bin/mypy", line 7, in <module>
+   File "/tmp/mypy_primer/mypy_new/venv/bin/mypy", line 7, in <module>
-   File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/__main__.py", line 15, in console_entry
+   File "/tmp/mypy_primer/mypy_new/venv/lib/python3.13/site-packages/mypy/__main__.py", line 15, in console_entry
-   File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/main.py", line 127, in main
+   File "/tmp/mypy_primer/mypy_new/venv/lib/python3.13/site-packages/mypy/main.py", line 127, in main
-   File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/main.py", line 211, in run_build
+   File "/tmp/mypy_primer/mypy_new/venv/lib/python3.13/site-packages/mypy/main.py", line 211, in run_build
-   File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/build.py", line 196, in build
+   File "/tmp/mypy_primer/mypy_new/venv/lib/python3.13/site-packages/mypy/build.py", line 196, in build
-   File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/build.py", line 272, in _build
+   File "/tmp/mypy_primer/mypy_new/venv/lib/python3.13/site-packages/mypy/build.py", line 272, in _build
-   File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/build.py", line 2946, in dispatch
+   File "/tmp/mypy_primer/mypy_new/venv/lib/python3.13/site-packages/mypy/build.py", line 2946, in dispatch
-   File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/build.py", line 3346, in process_graph
+   File "/tmp/mypy_primer/mypy_new/venv/lib/python3.13/site-packages/mypy/build.py", line 3346, in process_graph
-   File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/build.py", line 3475, in process_stale_scc
+   File "/tmp/mypy_primer/mypy_new/venv/lib/python3.13/site-packages/mypy/build.py", line 3475, in process_stale_scc
-   File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/build.py", line 2493, in write_cache
+   File "/tmp/mypy_primer/mypy_new/venv/lib/python3.13/site-packages/mypy/build.py", line 2493, in write_cache
-   File "/tmp/mypy_primer/mypy_old/venv/lib/python3.13/site-packages/mypy/cache.py", line 28, in __init__
+   File "/tmp/mypy_primer/mypy_new/venv/lib/python3.13/site-packages/mypy/cache.py", line 28, in __init__