## Summary
Adds proper type inference for implicit instance attributes that are
declared with a "bare" `Final` and adds `invalid-assignment` diagnostics
for all implicit instance attributes that are declared `Final` or
`Final[…]`.
## Test Plan
New and updated MD tests.
## Ecosystem analysis
```diff
pytest (https://github.com/pytest-dev/pytest)
+ error[invalid-return-type] src/_pytest/fixtures.py:1662:24: Return type does not match returned value: expected `Scope`, found `Scope | (Unknown & ~None & ~((...) -> object) & ~str) | (((str, Config, /) -> Unknown) & ~((...) -> object) & ~str) | (Unknown & ~str)
```
The definition of the `scope` attribute is [here](
5f99385635/src/_pytest/fixtures.py (L1020-L1028)).
Looks like this is a new false positive due to missing `TypeAlias`
support that is surfaced here because we now infer a more precise type
for `FixtureDef._scope`.
## Summary
Implement expansion of enums into unions of enum literals (and the
reverse operation). For the enum below, this allows us to understand
that `Color = Literal[Color.RED, Color.GREEN, Color.BLUE]`, or that
`Color & ~Literal[Color.RED] = Literal[Color.GREEN, Color.BLUE]`. This
helps in exhaustiveness checking, which is why we see some removed
`assert_never` false positives. And since exhaustiveness checking also
helps with understanding terminal control flow, we also see a few
removed `invalid-return-type` and `possibly-unresolved-reference` false
positives. This PR also adds expansion of enums in overload resolution
and type narrowing constructs.
```py
from enum import Enum
from typing_extensions import Literal, assert_never
from ty_extensions import Intersection, Not, static_assert, is_equivalent_to
class Color(Enum):
RED = 1
GREEN = 2
BLUE = 3
type Red = Literal[Color.RED]
type Green = Literal[Color.GREEN]
type Blue = Literal[Color.BLUE]
static_assert(is_equivalent_to(Red | Green | Blue, Color))
static_assert(is_equivalent_to(Intersection[Color, Not[Red]], Green | Blue))
def color_name(color: Color) -> str: # no error here (we detect that this can not implicitly return None)
if color is Color.RED:
return "Red"
elif color is Color.GREEN:
return "Green"
elif color is Color.BLUE:
return "Blue"
else:
assert_never(color) # no error here
```
## Performance
I avoided an initial regression here for large enums, but the
`UnionBuilder` and `IntersectionBuilder` parts can certainly still be
optimized. We might want to use the same technique that we also use for
unions of other literals. I didn't see any problems in our benchmarks so
far, so this is not included yet.
## Test Plan
Many new Markdown tests
## Summary
Emit errors for the following assignments:
```py
class C:
CLASS_LEVEL_CONSTANT: Final[int] = 1
C.CLASS_LEVEL_CONSTANT = 2
C().CLASS_LEVEL_CONSTANT = 2
```
## Test Plan
Updated and new MD tests
* [x] basic handling
* [x] parse and discover `@warnings.deprecated` attributes
* [x] associate them with function definitions
* [x] associate them with class definitions
* [x] add a new "deprecated" diagnostic
* [x] ensure diagnostic is styled appropriately for LSPs
(DiagnosticTag::Deprecated)
* [x] functions
* [x] fire on calls
* [x] fire on arbitrary references
* [x] classes
* [x] fire on initializers
* [x] fire on arbitrary references
* [x] methods
* [x] fire on calls
* [x] fire on arbitrary references
* [ ] overloads
* [ ] fire on calls
* [ ] fire on arbitrary references(??? maybe not ???)
* [ ] only fire if the actual selected overload is deprecated
* [ ] dunder desugarring (warn on deprecated `__add__` if `+` is
invoked)
* [ ] alias supression? (don't warn on uses of variables that deprecated
items were assigned to)
* [ ] import logic
* [x] fire on imports of deprecated items
* [ ] suppress subsequent diagnostics if the import diagnostic fired (is
this handled by alias supression?)
* [x] fire on all qualified references (`module.mydeprecated`)
* [x] fire on all references that depend on a `*` import
Fixes https://github.com/astral-sh/ty/issues/153
Fixes https://github.com/astral-sh/ty/issues/769.
**Updated:** The preferred approach here is to keep the SemanticIndex
simple (`del` of any name marks that name "bound" in the current scope)
and to move complexity to type inference (free variable resolution stops
when it finds a binding, unless that binding is declared `nonlocal`). As
part of this change, free variable resolution will now union the types
it finds as it walks in enclosing scopes. This approach is still
incomplete, because it doesn't consider inner scopes or sibling scopes,
but it improves the common case.
---------
Co-authored-by: Carl Meyer <carl@astral.sh>
## Summary
Resolves https://github.com/astral-sh/ty/issues/339
Supports having a blank function body inside `if TYPE_CHECKING` block or
in the elif or else of a `if not TYPE_CHECKING` block.
```py
if TYPE_CHECKING:
def foo() -> int: ...
if not TYPE_CHECKING: ...
else:
def bar() -> int: ...
```
## Test Plan
Update `function/return_type.md`
---------
Co-authored-by: Carl Meyer <carl@astral.sh>
Previously this worked if there was also a binding in the same scope as
the `global` declaration (probably almost always the case), but CPython
doesn't require this.
This change surfaced an error in an existing test, where a global
variable was only ever declared and bound using the `global` keyword,
and never mentioned explicitly in the global scope. @AlexWaygood
suggested we probably want to keep that requirement, so I'm adding an a
new test for that on top of fixing the failing test.
## Summary
Add a new `Type::EnumLiteral(…)` variant and infer this type for member
accesses on enums.
**Example**: No more `@Todo` types here:
```py
from enum import Enum
class Answer(Enum):
YES = 1
NO = 2
def is_yes(self) -> bool:
return self == Answer.YES
reveal_type(Answer.YES) # revealed: Literal[Answer.YES]
reveal_type(Answer.YES == Answer.NO) # revealed: Literal[False]
reveal_type(Answer.YES.is_yes()) # revealed: bool
```
## Test Plan
* Many new Markdown tests for the new type variant
* Added enum literal types to property tests, ran property tests
## Ecosystem analysis
Summary:
Lots of false positives removed. All of the new diagnostics are
either new true positives (the majority) or known problems. Click for
detailed analysis</summary>
Details:
```diff
AutoSplit (https://github.com/Toufool/AutoSplit)
+ error[call-non-callable] src/capture_method/__init__.py:137:9: Method `__getitem__` of type `bound method CaptureMethodDict.__getitem__(key: Never, /) -> type[CaptureMethodBase]` is not callable on object of type `CaptureMethodDict`
+ error[call-non-callable] src/capture_method/__init__.py:147:9: Method `__getitem__` of type `bound method CaptureMethodDict.__getitem__(key: Never, /) -> type[CaptureMethodBase]` is not callable on object of type `CaptureMethodDict`
+ error[call-non-callable] src/capture_method/__init__.py:148:1: Method `__getitem__` of type `bound method CaptureMethodDict.__getitem__(key: Never, /) -> type[CaptureMethodBase]` is not callable on object of type `CaptureMethodDict`
```
New true positives. That `__getitem__` method is apparently annotated
with `Never` to prevent developers from using it.
```diff
dd-trace-py (https://github.com/DataDog/dd-trace-py)
+ error[invalid-assignment] ddtrace/vendor/psutil/_common.py:29:5: Object of type `None` is not assignable to `Literal[AddressFamily.AF_INET6]`
+ error[invalid-assignment] ddtrace/vendor/psutil/_common.py:33:5: Object of type `None` is not assignable to `Literal[AddressFamily.AF_UNIX]`
```
Arguably true positives:
e0a772c28b/ddtrace/vendor/psutil/_common.py (L29)
```diff
ignite (https://github.com/pytorch/ignite)
+ error[invalid-argument-type] tests/ignite/engine/test_custom_events.py:190:34: Argument to bound method `__call__` is incorrect: Expected `((...) -> Unknown) | None`, found `Literal["123"]`
+ error[invalid-argument-type] tests/ignite/engine/test_custom_events.py:220:37: Argument to function `default_event_filter` is incorrect: Expected `Engine`, found `None`
+ error[invalid-argument-type] tests/ignite/engine/test_custom_events.py:220:43: Argument to function `default_event_filter` is incorrect: Expected `int`, found `None`
+ error[call-non-callable] tests/ignite/engine/test_custom_events.py:561:9: Object of type `CustomEvents` is not callable
+ error[invalid-argument-type] tests/ignite/metrics/test_frequency.py:50:38: Argument to bound method `attach` is incorrect: Expected `Events`, found `CallableEventWithFilter`
```
All true positives. Some of them are inside `pytest.raises(TypeError,
…)` blocks 🙃
```diff
meson (https://github.com/mesonbuild/meson)
+ error[invalid-argument-type] unittests/internaltests.py:243:51: Argument to bound method `__init__` is incorrect: Expected `bool`, found `Literal[MachineChoice.HOST]`
+ error[invalid-argument-type] unittests/internaltests.py:271:51: Argument to bound method `__init__` is incorrect: Expected `bool`, found `Literal[MachineChoice.HOST]`
```
New true positives. Enum literals can not be assigned to `bool`, even if
their value types are `0` and `1`.
```diff
poetry (https://github.com/python-poetry/poetry)
+ error[invalid-assignment] src/poetry/console/exceptions.py:101:5: Object of type `Literal[""]` is not assignable to `InitVar[str]`
```
New false positive, missing support for `InitVar`.
```diff
prefect (https://github.com/PrefectHQ/prefect)
+ error[invalid-argument-type] src/integrations/prefect-dask/tests/test_task_runners.py:193:17: Argument is incorrect: Expected `StateType`, found `Literal[StateType.COMPLETED]`
```
This is confusing. There are two definitions
([one](74d8cd93ee/src/prefect/client/schemas/objects.py (L89-L100)),
[two](https://github.com/PrefectHQ/prefect/blob/main/src/prefect/server/schemas/states.py#L40))
of the `StateType` enum. Here, we're trying to assign one to the other.
I don't think that should be allowed, so this is a true positive (?).
```diff
python-htmlgen (https://github.com/srittau/python-htmlgen)
+ error[invalid-assignment] test_htmlgen/form.py:51:9: Object of type `str` is not assignable to attribute `autocomplete` of type `Autocomplete | None`
+ error[invalid-assignment] test_htmlgen/video.py:38:9: Object of type `str` is not assignable to attribute `preload` of type `Preload | None`
```
True positives. [The stubs are
wrong](01e3b911ac/htmlgen/form.pyi (L8-L10)).
These should not contain type annotations, but rather just `OFF = ...`.
```diff
rotki (https://github.com/rotki/rotki)
+ error[invalid-argument-type] rotkehlchen/tests/unit/test_serialization.py:62:30: Argument to bound method `deserialize` is incorrect: Expected `str`, found `Literal[15]`
```
New true positive.
```diff
vision (https://github.com/pytorch/vision)
+ error[unresolved-attribute] test/test_extended_models.py:302:17: Type `type[WeightsEnum]` has no attribute `DEFAULT`
+ error[unresolved-attribute] test/test_extended_models.py:302:58: Type `type[WeightsEnum]` has no attribute `DEFAULT`
```
Also new true positives. No `DEFAULT` member exists on `WeightsEnum`.
The initial implementation of `infer_nonlocal` landed in
https://github.com/astral-sh/ruff/pull/19112 fails to report an error
for this example:
```py
x = 1
def f():
# This is only a usage of `x`, not a definition. It shouldn't be
# enough to make the `nonlocal` statement below allowed.
print(x)
def g():
nonlocal x
```
Fix this by continuing to walk enclosing scopes when the place we've
found isn't bound, declared, or `nonlocal`.
## Summary
Adds a way to list all members of an `Enum` and implements almost all of
the mechanisms by which members are distinguished from non-members
([spec](https://typing.python.org/en/latest/spec/enums.html#defining-members)).
This has no effect on actual enums, so far.
## Test Plan
New Markdown tests using `ty_extensions.enum_members`.
## Summary
Change `ClassLiteral.into_callable` to also look for `__init__` functions
of type `Type::Callable` (such as synthesized `__init__` functions of
dataclasses).
Fixes https://github.com/astral-sh/ty/issues/760
## Test Plan
Add subtype test
---------
Co-authored-by: David Peter <mail@david-peter.de>
## Summary
Emit a diagnostic when a `Final`-qualified symbol is modified. This
first iteration only works for name targets. Tests with TODO comments
were added for attribute assignments as well.
related ticket: https://github.com/astral-sh/ty/issues/158
## Ecosystem impact
Correctly identified [modification of a `Final`
symbol](7b4164a5f2/sphinx/__init__.py (L44))
(behind a `# type: ignore`):
```diff
- warning[unused-ignore-comment] sphinx/__init__.py:44:56: Unused blanket `type: ignore` directive
```
And the same
[here](5471a37e82/src/trio/_core/_run.py (L128)):
```diff
- warning[unused-ignore-comment] src/trio/_core/_run.py:128:45: Unused blanket `type: ignore` directive
```
## Test Plan
New Markdown tests
## Summary
Fixes a bug where conditionally defined dataclass fields were previously
ignored.
Thanks to @lipefree for reporting this.
## Test Plan
New Markdown tests
## Summary
Related:
- https://github.com/astral-sh/ty/issues/111
- https://github.com/astral-sh/ruff/pull/17974#discussion_r2108527106
Previously, when validating an attribute assignment, a `__setattr__`
call check was only done if the attribute wasn't found as either a class
member or instance member
This PR changes the `__setattr__` call check to be attempted first,
prior to the "[normal
mechanism](https://docs.python.org/3/reference/datamodel.html#object.__setattr__)",
as a defined `__setattr__` should take precedence over setting an
attribute on the instance dictionary directly.
if the return type of `__setattr__` is `Never`, an `invalid-assignment`
diagnostic is emitted
Once this is merged, a subsequent PR will synthesize a `__setattr__`
method with a `Never` return type for frozen dataclasses.
## Test Plan
Existing tests + mypy_primer
---------
Co-authored-by: David Peter <mail@david-peter.de>
## Summary
It was recently clarified in the [typing
spec](https://typing.python.org/en/latest/spec/class-compat.html#classvar)
that bare `ClassVar` annotations are allowed. For annotated assignments
with a right hand side value, the spec requires type checkers to infer
the type as something "to which [the] value is assignable". For a value
of `2`, the spec suggests `int`, `Literal[2]`, or `Any` as examples.
Here, we choose `Unknown | Literal[2]` instead, conforming with out
usual treatment of attribute types.
closes https://github.com/astral-sh/ty/issues/211
## Summary
This PR implements the following pieces of `Protocol` semantics:
1. A protocol with a method member that does not have a fully static
signature should not be considered fully static. I.e., this protocol is
not fully static because `Foo.x` has no return type; we previously
incorrectly considered that it was:
```py
class Foo(Protocol):
def f(self): ...
```
2. Two protocols `P1` and `P2`, both with method members `x`, should be
considered equivalent if the signature of `P1.x` is equivalent to the
signature of `P2.x`. Currently we do not recognize this.
Implementing these semantics requires distinguishing between method
members and non-method members. The stored type of a method member must
be eagerly upcast to a `Callable` type when collecting the protocol's
interface: doing otherwise would mean that it would be hard to implement
equivalence of protocols even in the face of differently ordered unions,
since the two equivalent protocols would have different Salsa IDs even
when normalized.
The semantics implemented by this PR are that we consider something a
method member if:
1. It is accessible on the class itself; and
2. It is a function-like callable: a callable type that also has a
`__get__` method, meaning it can be used as a method when accessed on
instances.
Note that the spec has complicated things to say about classmethod
members and staticmethod members. These semantics are not implemented by
this PR; they are all deferred for now.
The infrastructure added in this PR fixes bugs in its own right, but
also lays the groundwork for implementing subtyping and assignability
rules for method members of protocols. A (currently failing) test is
added to verify this.
## Test Plan
mdtests
## Summary
Infer the type of symbols with a `Final` qualifier as their
right-hand-side inferred type:
```py
x: Final = 1
y: Final[int] = 1
def _():
reveal_type(x) # previously: Unknown, now: Literal[1]
reveal_type(y) # int, same as before
```
Part of https://github.com/astral-sh/ty/issues/158
## Ecosystem analysis
### aiohttp
```diff
aiohttp (https://github.com/aio-libs/aiohttp)
+ error[invalid-argument-type] aiohttp/compression_utils.py:131:54: Argument to bound method `__init__` is incorrect: Expected `ZLibBackendProtocol`, found `<module 'zlib'>`
```
This code [creates a
protocol](a83597fa88/aiohttp/compression_utils.py (L52-L77))
that looks like
```pyi
class ZLibBackendProtocol(Protocol):
Z_FULL_FLUSH: int
Z_SYNC_FLUSH: int
# more fields…
```
It then [tries to
assign](a83597fa88/aiohttp/compression_utils.py (L131))
the module literal `zlib` to that protocol. Howefer, in typeshed, these
`zlib` members are annotated like this:
```pyi
Z_FULL_FLUSH: Final = 3
Z_SYNC_FLUSH: Final = 2
```
With the proposed change here, we now infer these as `Literal[3]` /
`Literal[2]`. Since protocol members have to be assignable both ways
(invariance), we do not consider `zlib` assignable to this protocol
anymore.
That seems rather unfortunate. Not sure who is to blame here? That
`ZLibBackendProtocol` protocol should probably not annotate the members
with `int`, given that `typeshed` doesn't use an explicit annotation
here either? But what should they do instead? Annotate those fields with
`Any`?
Or is it another case where we should consider literal-widening?
FYI @AlexWaygood
### cloud-init
```diff
cloud-init (https://github.com/canonical/cloud-init)
+ error[invalid-argument-type] tests/unittests/sources/test_smartos.py:575:32: Argument to function `oct` is incorrect: Expected `SupportsIndex`, found `int | float`
+ error[invalid-argument-type] tests/unittests/sources/test_smartos.py:593:32: Argument to function `oct` is incorrect: Expected `SupportsIndex`, found `int | float`
+ error[invalid-argument-type] tests/unittests/sources/test_smartos.py:647:35: Argument to function `oct` is incorrect: Expected `SupportsIndex`, found `int | float`
```
New false positives on expressions like
`oct(os.stat(legacy_script_f)[stat.ST_MODE])`. We now correctly infer
`stat.ST_MODE` as `Literal[1]`, because in typeshed, it is annotated as
`ST_MODE: Final = 0`. `os.stat` returns a `stat_result` which is a tuple
subclass. Accessing it at index 0 should return an `int`, but we
currently return `int | float`, presumably due to missing support for
tuple subclasses (FYI @AlexWaygood):
```pyi
class stat_result(structseq[float], tuple[int, int, int, int, int, int, int, float, float, float]):
```
In terms of `typing.Final`, things are working as expected here.
### pywin-32
Many new false positives similar to:
```diff
pywin32 (https://github.com/mhammond/pywin32)
+ error[invalid-argument-type] Pythonwin/pywin/docking/DockingBar.py:288:55: Argument to function `LoadCursor` is incorrect: Expected `PyResourceId`, found `Literal[32645]`
```
The line in question calls `win32api.LoadCursor(0, win32con.IDC_ARROW)`.
The `win32con.IDC_ARROW` symbol is annotated as [`IDC_ARROW: Final =
32512` in
typeshed](2408c028f4/stubs/pywin32/win32/lib/win32con.pyi (L594)),
but
[`LoadCursor`](2408c028f4/stubs/pywin32/win32/win32api.pyi (L197))
expects a
[`PyResourceId`](2408c028f4/stubs/pywin32/_win32typing.pyi (L1252)),
which is an empty class. So.. this seems like a true positive to me,
unless that typeshed annotation of `IDC_ARROW` is meant to imply that
the type should be `Unknown`/`Any`?
### streamlit
```diff
streamlit (https://github.com/streamlit/streamlit)
+ error[invalid-argument-type] lib/streamlit/string_util.py:163:37: Argument to bound method `translate` is incorrect: Expected `bytes`, found `bytearray`
```
This looks like a true positive? The code calls `inp.translate(None,
TEXTCHARS)`. `inp` is `bytes`, and `TEXTCHARS` is:
```py
TEXTCHARS: Final = bytearray(
{7, 8, 9, 10, 12, 13, 27} | set(range(0x20, 0x100)) - {0x7F}
)
```
~~We now infer this as `bytearray`, but `bytes.translate` [expects
`bytes` for its `delete`
parameter](2408c028f4/stdlib/builtins.pyi (L710)).
This seems to work at runtime, so maybe the typeshed annotation is
wrong?~~ (Edit: this is now fixed in typeshed)
```pycon
>>> b"abc".translate(None, bytearray(b"b"))
b'ac'
```
## rotki
```diff
+ error[invalid-return-type] rotkehlchen/chain/ethereum/modules/yearn/decoder.py:412:13: Return type does not match returned value: expected `dict[Unknown, str]`, found `dict[Unknown, Literal["yearn-v1", "yearn-v2"]]`
```
The code in question looks like
```py
def addresses_to_counterparties(self) -> dict[ChecksumEvmAddress, str]:
return dict.fromkeys(self.vaults, CPT_BEEFY_FINANCE)
```
where `CPT_BEEFY_FINANCE: Final = 'beefy_finance'. We previously
inferred the value type of the returned `dict` as `Unknown`, and now we
infer it as `Literal["beefy_finance"]`, which does not match the
annotated return type because `dict` is invariant in the value type.
```diff
+ error[invalid-argument-type] rotkehlchen/tests/unit/decoders/test_curve.py:249:9: Argument is incorrect: Expected `int`, found `FVal`
```
There are true positives that were previously silenced through the
`Unknown`.
## Test Plan
New Markdown tests
## Summary
Following ty issue [#698](https://github.com/astral-sh/ty/issues/698)
this PR adds support for declarations.
closes#698
## Test Plan
Tested against mdtest (specifically attributes).
---------
Co-authored-by: David Peter <mail@david-peter.de>
## Summary
`ty` does not understand that calls to functions which have been
annotated as having a return type of `Never` / `NoReturn` are terminal.
This PR fixes that, by adding new reachability constraints when call
expressions are seen. If the call expression evaluates to `Never`, the
code following it will be considered to be unreachable. Note that, for
adding these constraints, we only consider call expressions at the
statement level, and that too only inside function scopes. This is
because otherwise, the number of such constraints becomes too high, and
evaluating them later on during type inference results in a major
performance degradation.
Fixes https://github.com/astral-sh/ty/issues/180
## Test Plan
New mdtests.
## Ecosystem changes
This PR removes the following false-positives:
- "Function can implicitly return `None`, which is not assignable to
...".
- "Name `foo` used when possibly not defind" - because the branch in
which it is not defined has a `NoReturn` call, or when `foo` was
imported in a `try`, and the except had a `NoReturn` call.
---------
Co-authored-by: David Peter <mail@david-peter.de>
## Summary
Part of https://github.com/astral-sh/ty/issues/129
There were previously some false positives here.
## Test Plan
Updated `is_subtype_of.md` and `is_assignable_to.md`
## Summary
Allow declared-only class-level attributes to be accessed on the class:
```py
class C:
attr: int
C.attr # this is now allowed
```
closes https://github.com/astral-sh/ty/issues/384
closes https://github.com/astral-sh/ty/issues/553
## Ecosystem analysis
* We see many removed `unresolved-attribute` false-positives for code
that makes use of sqlalchemy, as expected (see changes for `prefect`)
* We see many removed `call-non-callable` false-positives for uses of
`pytest.skip` and similar, as expected
* Most new diagnostics seem to be related to cases like the following,
where we previously inferred `int` for `Derived().x`, but now we infer
`int | None`. I think this should be a
conflicting-declarations/bad-override error anyway? The new behavior may
even be preferred here?
```py
class Base:
x: int | None
class Derived(Base):
def __init__(self):
self.x: int = 1
```
## Summary
Remove a hack in control flow modeling that was treating `return`
statements at the end of function bodies in a special way (basically
considering the state *just before* the `return` statement as the
end-of-scope state). This is not needed anymore now that #18750 has been
merged.
In order to make this work, we now use *all reachable bindings* for
purposes of finding implicit instance attribute assignments as well as
for deferred lookups of symbols. Both would otherwise be affected by
this change:
```py
def C:
def f(self):
self.x = 1 # a reachable binding that is not visible at the end of the scope
return
```
```py
def f():
class X: ... # a reachable binding that is not visible at the end of the scope
x: "X" = X() # deferred use of `X`
return
```
Implicit instance attributes also required another change. We previously
kept track of possibly-unbound instance attributes in some cases, but we
now give up on that completely and always consider *implicit* instance
attributes to be bound if we see a reachable binding in a reachable
method. The previous behavior was somewhat inconsistent anyway because
we also do not consider attributes possibly-unbound in other scenarios:
we do not (and can not) keep track of whether or not methods are called
that define these attributes.
closes https://github.com/astral-sh/ty/issues/711
## Ecosystem analysis
I think this looks very positive!
* We see an unsurprising drop in `possibly-unbound-attribute`
diagnostics (599), mostly for classes that define attributes in `try …
except` blocks, `for` loops, or `if … else: raise …` constructs. There
might obviously also be true positives that got removed, but the vast
majority should be false positives.
* There is also a drop in `possibly-unresolved-reference` /
`unresolved-reference` diagnostics (279+13) from the change to deferred
lookups.
* Some `invalid-type-form` false positives got resolved (13), because we
can now properly look up the names in the annotations.
* There are some new *true* positives in `attrs`, since we understand
the `Attribute` annotation that was previously inferred as `Unknown`
because of a re-assignment after the class definition.
## Test Plan
The existing attributes.md test suite has sufficient coverage here.
