Consistently store settable property type

[ilevkivskyi]

Fixes #18764

There are two things important to understand this PR:

• First, mypy has a performance optimization - we store decorator/overload type during semantic analysis in certain "trivial" situations (to avoid deferrals). Otherwise, we infer the type of decorated function or an overload variant during type checking.
• Second, for settable properties we store getter type in two places, as a Var.type of getter (as a decorator), and also in overall OverloadedFuncDef.type. The latter is ugly, but unfortunately it is hard to get rid of, since some code in multiple plugins rely on this.

It turns out there are three inconsistencies in how these two things interact (first one causes the actual crash):

• For trivial settable properties (i.e. without extra decorators) when we store the type in semanal.py we only store it the second way (i.e. as OverloadedFuncDef.type).
• For non-trivial settable properties (where getter and/or setter are themselves decorated), we only set the inferred type the first way (as Var.type).
• When inferring setter type (unlike getter, that is handled correctly) we actually ignore any extra decorators (this is probably quire niche, but still inconsistent).

Essentially I simply remove these inconsistencies.

[hauntsaninja]

Thank you for fixing! Confirmed that this fixes the original crash 🙏

[hauntsaninja]

Nice, looks like a lot of the aiohttp primer is from the check_untyped_after_decorator change

[ilevkivskyi]

Change in prefect looks like a new false negative (I know how to fix this, but it also makes me think that we currently implicitly rely on setter being second, but it also may be third, after the deleter).

The couple new errors in xarray look like a new false positive. But TBH I don't feel like chasing this one, as the same error would appear if they had --local-partial-types enabled.

[ilevkivskyi]

OK, I actually checked the xarray thing, it turns out to be some weird bug in --show-error-context causing errors to be shown twice. A similar problem exists on master. So to avoid scope creep, I am not trying to fix it (and also the setter vs deleter ordering, I just add a TODO).

[github-actions]

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

aiohttp (https://github.com/aio-libs/aiohttp)
+ aiohttp/abc.py:84: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/web_routedef.py:57: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/web_routedef.py:82: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/helpers.py:148: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/helpers.py:177: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/helpers.py:248: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/helpers.py:873: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/helpers.py:890: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/client_reqrep.py:325: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/client.py:1250: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/client.py:1287: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/web_server.py:43: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/web_server.py:52: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/web_app.py:167: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/web_app.py:182: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/web_app.py:216: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/web_runner.py:257: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/worker.py:203: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/test_utils.py:160: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/test_utils.py:270: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/test_utils.py:278: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/pytest_plugin.py:45: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/pytest_plugin.py:53: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/pytest_plugin.py:402: error: Unused "type: ignore" comment  [unused-ignore]
+ aiohttp/pytest_plugin.py:409: error: Unused "type: ignore" comment  [unused-ignore]

xarray (https://github.com/pydata/xarray)
+ xarray/core/variable.py: note: In function "encoding":
+ xarray/core/variable.py:857: error: Incompatible types in assignment (expression has type "dict[Never, Never]", variable has type "None")  [assignment]
+ xarray/core/variable.py:858: error: Incompatible return value type (got "None", expected "dict[Any, Any]")  [return-value]

trio (https://github.com/python-trio/trio)
+ src/trio/_file_io.py:431: error: Unused "type: ignore[misc]" comment  [unused-ignore]
+ src/trio/_path.py:186: error: Unused "type: ignore[misc]" comment  [unused-ignore]

[cdce8p]

This change seems to cause another crash unfortunately. Noticed this first for Home Assistant with

# pip install qbittorrent-api==2024.2.59
from qbittorrentapi.transfer import Transfer

Was able to reproduce it with

from functools import wraps

def transfer_speed_limits_mode(): ...
def transfer_set_speed_limits_mode(): ...

class Transfer:
    @property
    @wraps(transfer_speed_limits_mode)
    def speed_limits_mode(self) -> str:
        ...

    @speed_limits_mode.setter
    @wraps(transfer_set_speed_limits_mode)
    def speed_limits_mode(self, val: bool) -> None:
        ...

$ mypy --show-traceback --no-incremental test.py 
test.py:9: error: Missing return statement  [empty-body]
test.py:7: error: INTERNAL ERROR -- Please try using mypy master on GitHub:
https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 1.16.0+dev.af5186e1bccdc3983a289bea962bb940ef6857f8
Traceback (most recent call last):
  File "mypy/checker.py", line 576, in accept
    stmt.accept(self)
  File "mypy/nodes.py", line 580, in accept
    return visitor.visit_overloaded_func_def(self)
  File "mypy/checker.py", line 641, in visit_overloaded_func_def
    self._visit_overloaded_func_def(defn)
  File "mypy/checker.py", line 711, in _visit_overloaded_func_def
    assert isinstance(var_type, CallableType)
AssertionError: 
test.py:7: : note: use --pdb to drop into pdb

Do note though that I was only able to reproduce it with a compiled build
https://github.com/mypyc/mypy_mypyc-wheels/releases/tag/v1.16.0%2Bdev.af5186e1bccdc3983a289bea962bb940ef6857f8

mypy 1.16.0+dev.af5186e1bccdc3983a289bea962bb940ef6857f8 (compiled: yes)

[ilevkivskyi]

OK, fair enough, I just need to do the same fallback dance I do for the setter (and I can actually make it precise as we only care about the return type).