[ty] Support attribute-expression TYPE_CHECKING conditionals

[AlexWaygood]

Summary

A simpler alternative to #19412, that gets rid of lots of false positives.

We now treat if foo.bar.baz.spam.eggs.TYPE_CHECKING the same as if TYPE_CHECKING.

Test Plan

Added mdtests

Ecosystem impact

Lots of invalid-return-type false positives go away for things like this:

import typing as t

if t.TYPE_CHECKING:
    def f() -> str: ...

[astral-sh-bot]

Diagnostic diff on typing conformance tests

No changes detected when running ty on typing conformance tests ✅

[astral-sh-bot]

mypy_primer results

Changes were detected when running on open source projects

bidict (https://github.com/jab/bidict)
- bidict/_bidict.py:41:30: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `MutableBidict[VT@MutableBidict, KT@MutableBidict]`
- bidict/_bidict.py:44:26: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `MutableBidict[VT@MutableBidict, KT@MutableBidict]`
- bidict/_bidict.py:185:30: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `bidict[VT@bidict, KT@bidict]`
- bidict/_bidict.py:188:26: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `bidict[VT@bidict, KT@bidict]`
- bidict/_frozen.py:34:30: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `frozenbidict[VT@frozenbidict, KT@frozenbidict]`
- bidict/_frozen.py:37:26: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `frozenbidict[VT@frozenbidict, KT@frozenbidict]`
- bidict/_orderedbase.py:138:30: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `OrderedBidictBase[VT@OrderedBidictBase, KT@OrderedBidictBase]`
- bidict/_orderedbase.py:141:26: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `OrderedBidictBase[VT@OrderedBidictBase, KT@OrderedBidictBase]`
- bidict/_orderedbidict.py:39:30: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `OrderedBidict[VT@OrderedBidict, KT@OrderedBidict]`
- bidict/_orderedbidict.py:42:26: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `OrderedBidict[VT@OrderedBidict, KT@OrderedBidict]`
- Found 25 diagnostics
+ Found 15 diagnostics

spack (https://github.com/spack/spack)
- lib/spack/spack/vendor/jinja2/bccache.py:26:36: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `bytes`
- lib/spack/spack/vendor/jinja2/ext.py:27:44: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `str`
- lib/spack/spack/vendor/jinja2/ext.py:30:67: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `str`
- lib/spack/spack/vendor/jinja2/ext.py:34:59: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `str`
- lib/spack/spack/vendor/jinja2/ext.py:37:82: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `str`
- lib/spack/spack/vendor/jinja2/filters.py:38:31: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `str`
- lib/spack/spack/vendor/jinja2/runtime.py:40:14: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `str`
- lib/spack/spack/vendor/markupsafe/__init__.py:10:31: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `str`
- Found 7911 diagnostics
+ Found 7903 diagnostics

jinja (https://github.com/pallets/jinja)
- src/jinja2/ext.py:34:59: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `str`
- src/jinja2/ext.py:38:14: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `str`
- Found 181 diagnostics
+ Found 179 diagnostics

meson (https://github.com/mesonbuild/meson)
- mesonbuild/compilers/d.py:110:44: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `list[str]`
- mesonbuild/linkers/linkers.py:634:68: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `list[str]`
- mesonbuild/linkers/linkers.py:1372:68: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `list[str]`
- mesonbuild/options.py:402:36: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `int`
- Found 1734 diagnostics
+ Found 1730 diagnostics

No memory usage changes detected ✅

[astral-sh-bot]

ecosystem-analyzer results

Lint rule	Added	Removed	Changed
invalid-return-type	0	24	0
Total	0	24	0

Full report with detailed diff (timing results)

[sharkdp]

Thank you!