Fix Enum.value inference for Enums with @cached methods

[kmurphy4]

Before this, adding an annotation like @functools.cache to any method on an Enum caused the inference for the class's .value to fail (i.e., become Any).

Fixes #19368

[kmurphy4]

Should I add something to the changelog? I think this is a user-facing change.

[github-actions]

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

[sterliakov]

We build changelog from the commit history, like #19138, so no need to add CHANGELOG entries in every PR:)

[sterliakov]

I'm not sure this check is still needed - can there be any enum_members that are implicit? That should never happen AFAIC

[kmurphy4]

Seems like it is? With

diff --git i/mypy/plugins/enums.py w/mypy/plugins/enums.py
index 35338d091..c6e9f21b6 100644
--- i/mypy/plugins/enums.py
+++ w/mypy/plugins/enums.py
@@ -192,7 +192,7 @@ def enum_value_callback(ctx: mypy.plugin.AttributeContext) -> Type:
             node_types = (
                 get_proper_type(n.type) if n else None
                 for n in stnodes
-                if n is None or not n.implicit
+                if n is None
             )
             proper_types = [_infer_value_type_with_auto_fallback(ctx, t) for t in node_types]
             underlying_type = _first(proper_types)

I get

$ pytest -k testValueFallbackWithCachedMethod
============================= test session starts ==============================
platform linux -- Python 3.12.6, pytest-8.3.5, pluggy-1.6.0
rootdir: /home/kevinmurphy/src/python/mypy
configfile: pyproject.toml
testpaths: mypy/test, mypyc/test
plugins: xdist-3.7.0, cov-6.1.1
6 workers [1 item]      
F                                                                        [100%]
=================================== FAILURES ===================================
______________________ testValueFallbackWithCachedMethod _______________________
[gw0] linux -- Python 3.12.6 /home/kevinmurphy/src/python/mypy/venv/bin/python3
data: /home/kevinmurphy/src/python/mypy/test-data/unit/check-enum.test:2543:
Failed: Unexpected type checker output (/home/kevinmurphy/src/python/mypy/test-data/unit/check-enum.test, line 2543)
----------------------------- Captured stderr call -----------------------------
Expected:
  main:19: note: Revealed type is "builtins.int"
  main:22: note: Revealed type is "builtins.int" (diff)
Actual:
  main:19: note: Revealed type is "builtins.int"
  main:22: note: Revealed type is "Any" (diff)

Alignment of first line difference:
  E: ...ote: Revealed type is "builtins.int"
  A: ...ote: Revealed type is "Any"
                               ^
Update the test output using --update-data (implies -n0; you can additionally use the -k selector to update only specific tests)
=========================== short test summary info ============================
FAILED mypy/test/testcheck.py::TypeCheckSuite::check-enum.test::testValueFallbackWithCachedMethod
============================== 1 failed in 2.26s ===============================