## Summary
This PR does the following things:
- Fixes the `python` configuration setting for mdtest (added in
https://github.com/astral-sh/ruff/pull/17221) so that it expects a path
pointing to a venv's `sys.prefix` variable rather than the a path
pointing to the venv's `site-packages` subdirectory. This brings the
`python` setting in mdtest in sync with our CLI `--python` flag.
- Tweaks mdtest so that it automatically creates a valid `pyvenv.cfg`
file for you if you don't specify one. This makes it much more ergonomic
to write an mdtest with a custom `python` setting: red-knot will reject
a `python` setting that points to a directory that doesn't have a
`pyvenv.cfg` file in it
- Tweaks mdtest so that it doesn't check a custom `pyvenv.cfg` as Python
source code if you _do_ add a custom `pyvenv.cfg` file for your mock
virtual environment in an mdtest. (You get a lot of diagnostics about
Python syntax errors in the `pyvenv.cfg` file, otherwise!)
- Rewrites the test added in
https://github.com/astral-sh/ruff/pull/17178 as an mdtest, and deletes
the original test that was added in that PR
## Test Plan
I verified that the new mdtest fails if I revert the changes to
`resolver.rs` that were added in
https://github.com/astral-sh/ruff/pull/17178
## Summary
This PR fixes the cycle issue that was causing problems in the `support
super` PR.
### Affected queries
- `all_narrowing_constraints_for_expression`
- `all_negative_narrowing_constraints_for_expression`
--
Additionally, `bidict` and `werkzeug` have been added to the
project-selection list in `mypy_primer`.
This PR also addresses the panics that occurred while analyzing those
packages:
- `bidict`: panic triggered by
`all_narrowing_constraints_for_expression`
- `werkzeug`: panic triggered by
`all_negative_narrowing_constraints_for_expression`
I think the mypy-primer results for this PR can serve as sufficient test
:)
## Summary
This is a follow up to the goto type definition PR. Specifically, that
we want to avoid exposing too many semantic model internals publicly.
I want to get some feedback on the approach taken. I think it goes into
the right direction but I'm not super happy with it.
The basic idea is that we add a `Type::definition` method which does the
"goto type definition". The parts that I think make it awkward:
* We can't directly return `Definition` because we don't create a
`Definition` for modules (but we could?). Although I think it makes
sense to possibly have a more public wrapper type anyway?
* It doesn't handle unions and intersections. Mainly because not all
elements in an intersection may have a definition and we only want to
show a navigation target for intersections if there's only a single
positive element (besides maybe `Unknown`).
An alternative design or an addition to this design is to introduce a
`SemanticAnalysis(Db)` struct that has methods like
`type_definition(&self, type)` which explicitly exposes the methods we
want. I don't feel comfortable design this API yet because it's unclear
how fine granular it has to be (and if it is very fine granular,
directly using `Type` might be better after all)
## Test Plan
`cargo test`
For two non-disjoint types `P` and `Q`, the simplification of `(P | Q) &
~Q` is not `P`, but `P & ~Q`. In other words, the non-empty set `P & Q`
is also excluded from the type.
The same applies for a constrained typevar `[T: (P, Q)]`: `T & ~Q`
should simplify to `P & ~Q`, not just `P`.
Implementing this is actually purely a matter of removing code from the
constrained typevar simplification logic; we just need to not bother
removing the negations. If the negations are actually redundant (because
the constraint types are disjoint), normal intersection simplification
will already eliminate them (as shown in the added test.)
## Summary
It turns out that `a.` isn't a list format supported by rustdoc. I
changed the documentation to use `1.`, `2.` instead.
## Test Plan
`cargo clippy`
This adds a new `Type` variant for holding an instance of a typevar
inside of a generic function or class. We don't handle specializing the
typevars yet, but this should implement most of the typing rules for
inside the generic function/class, where we don't know yet which
specific type the typevar will be specialized to.
This PR does _not_ yet handle the constraint that multiple occurrences
of the typevar must be specialized to the _same_ time. (There is an
existing test case for this in `generics/functions.md` which is still
marked as TODO.)
---------
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
Co-authored-by: Carl Meyer <carl@astral.sh>
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## Summary
I decided to disable the new
[`needless_continue`](https://rust-lang.github.io/rust-clippy/master/index.html#needless_continue)
rule because I often found the explicit `continue` more readable over an
empty block or having to invert the condition of an other branch.
## Test Plan
`cargo test`
---------
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
## Summary
This PR changes the inferred type for symbols in unreachable sections of
code to `Never` (instead of reporting them as unbound), in order to
silence false positive diagnostics. See the lengthy comment in the code
for further details.
## Test Plan
- Updated Markdown tests.
- Manually verified a couple of ecosystem diagnostic changes.
## Summary
If a package in `site-packages` had this directory structure:
```py
# bar/__init__.py
from .a import A
# bar/a.py
class A: ...
```
then we would fail to resolve the `from .a import A` import _if_ (as is
usually the case!) the `site-packages` search path was located inside a
`.venv` directory that was a subdirectory of the project's first-party
search path. The reason for this is a bug in `file_to_module` in the
module resolver. In this loop, we would identify that
`/project_root/.venv/lib/python3.13/site-packages/foo/__init__.py` can
be turned into a path relative to the first-party search path
(`/project_root`):
6e2b8f9696/crates/red_knot_python_semantic/src/module_resolver/resolver.rs (L101-L110)
but we'd then try to turn the relative path
(.venv/lib/python3.13/site-packages/foo/__init__.py`) into a module
path, realise that it wasn't a valid module path... and therefore
immediately `break` out of the loop before trying any other search paths
(such as the `site-packages` search path).
This bug was originally reported on Discord by @MatthewMckee4.
## Test Plan
I added a unit test for `file_to_module` in `resolver.rs`, and an
integration test that shows we can now resolve the import correctly in
`infer.rs`.
Fixes#17164. Simply checking whether one type is gradually equivalent
to another is too simplistic here: `Any` is gradually equivalent to
`Todo`, but we should permit users to cast from `Todo` or `Unknown` to
`Any` without complaining about it. This changes our logic so that we
only complain about redundant casts if:
- the two types are exactly equal (when normalized) OR they are
equivalent (we'll still complain about `Any -> Any` casts, and about
`Any | str | int` -> `str | int | Any` casts, since their normalized
forms are exactly equal, even though the type is not fully static -- and
therefore does not participate in equivalence relations)
- AND the casted type does not contain `Todo`
## Summary
The existing signature for `str` calls had various problems, one of
which I noticed while looking at some ecosystem projects (`scrapy`,
added as a project to mypy_primer in this PR).
## Test Plan
- New tests for `str(…)` calls.
- Observed reduction of false positives in ecosystem checks
## Summary
A callable type is disjoint from other literal types. For example,
`Type::StringLiteral` must be an instance of exactly `str`, not a
subclass of `str`, and `str` is not callable. The same applies to other
literal types.
This should hopefully fix#17144, I couldn't produce any failures after
running property tests multiple times.
## Test Plan
Add test cases for disjointness check between callable and other literal
types.
Run property tests multiple times.
## Summary
Python `**` works differently to Rust `**`!
## Test Plan
Added an mdtest for various edge cases, and checked in the Python REPL
that we infer the correct type in all the new cases tested.
## Summary
This PR adds a CI job that causes GitHub to add annotations to a PR diff
when mdtest assertions fail. For example:
<details>
<summary>Screenshot</summary>
</details>
## Motivation
Debugging mdtest failures locally is currently a really nice experience:
- Errors are displayed with pretty colours, which makes them much more
readable
- If you run the test from inside an IDE, you can CTRL-click on a path
and jump directly to the line that had the failing assertion
- If you use
[`mdtest.py`](https://github.com/astral-sh/ruff/blob/main/crates/red_knot_python_semantic/mdtest.py),
you don't even need to recompile anything after changing an assertion in
an mdtest, amd the test results instantly live-update with each change
to the MarkDown file
Debugging mdtest failures in CI is much more unpleasant, however.
Sometimes an error message is just
> [static-assert-error] Argument evaluates to `False`
...which doesn't tell you very much unless you navigate to the line in
question that has the failing mdtest assertion. The line in question
might not even be touched by the PR, and even if it is, it can be hard
to find the line if the PR touches many files. Unlike locally, you can't
click on the error and jump straight to the line that contains the
failing assertion. You also don't get colourised output in CI
(https://github.com/astral-sh/ruff/issues/13939).
GitHub PR annotations should make it really easy to debug why mdtests
are failing on PRs, making PR review much easier.
## Test Plan
I opened a PR to my fork
[here](https://github.com/AlexWaygood/ruff/pull/11/files) with some
bogus changes to an mdtest to show what it looks like when there are
failures in CI and this job has been added. Scroll down to
`crates/red_knot_python_semantic/resources/mdtest/type_properties/is_equivalent_to.md`
on the "files changed" tab for that PR to see the annotations.
## Summary
Fixes https://github.com/astral-sh/ruff/issues/17058.
Equivalent callable types were not understood as equivalent when they
appeared nested inside unions and intersections. This PR fixes that by
ensuring that `Callable` elements nested inside unions, intersections
and tuples have their representations normalized before one union type
is compared with another for equivalence, or before one intersection
type is compared with another for equivalence.
The normalizations applied to a `Callable` type are:
- the type of the default value is stripped from all parameters (only
whether the parameter _has_ a default value is relevant to whether one
`Callable` type is equivalent to another)
- The names of the parameters are stripped from positional-only
parameters, variadic parameters and keyword-variadic parameters
- Unions and intersections that are present (top-level or nested) inside
parameter annotations or return annotations are normalized.
Adding a `CallableType::normalized()` method also allows us to simplify
the implementation of `CallableType::is_equivalent_to()`.
### Should these normalizations be done eagerly as part of a
`CallableType` constructor?
I considered this. It's something that we could still consider doing in
the future; this PR doesn't rule it out as a possibility. However, I
didn't pursue it for now, for several reasons:
1. Our current `Display` implementation doesn't handle well the
possibility that a parameter might not have a name or an annotated type.
Callable types with parameters like this would be displayed as follows:
```py
(, ,) -> None: ...
```
That's fixable! It could easily become something like `(Unknown,
Unknown) -> None: ...`. But it also illustrates that we probably want to
retain the parameter names when displaying the signature of a `lambda`
function if you're hovering over a reference to the lambda in an IDE.
Currently we don't have a `LambdaType` struct for representing `lambda`
functions; if we wanted to eagerly normalize signatures when creating
`CallableType`s, we'd probably have to add a `LambdaType` struct so that
we would retain the full signature of a `lambda` function, rather than
representing it as an eagerly simplified `CallableType`.
2. In order to ensure that it's impossible to create `CallableType`s
without the parameters being normalized, I'd either have to create an
alternative `SimplifiedSignature` struct (which would duplicate a lot of
code), or move `CallableType` to a new module so that the only way of
constructing a `CallableType` instance would be via a constructor method
that performs the normalizations eagerly on the callable's signature.
Again, this isn't a dealbreaker, and I think it's still an option, but
it would be a lot of churn, and it didn't seem necessary for now. Doing
it this way, at least to start with, felt like it would create a diff
that's easier to review and felt like it would create fewer merge
conflicts for others.
## Test Plan
- Added a regression mdtest for
https://github.com/astral-sh/ruff/issues/17058
- Ran `QUICKCHECK_TESTS=1000000 cargo test --release -p
red_knot_python_semantic -- --ignored types::property_tests::stable`
## Summary
Add an initial set of tests that will eventually document our behavior
around unreachable code. In the last section of this suite, I argue why
we should never type check unreachable sections and never emit any
diagnostics in these sections.
## Summary
With this PR, we emit a diagnostic for this case where
previously didn't:
```py
from typing import Literal
def f(m: int, n: Literal[-1, 0, 1]):
# error: [division-by-zero] "Cannot divide object of type `int` by zero"
return m / n
```
## Test Plan
New Markdown test
I put this in its own commit in case all of the information removed here
was controversial. But it *looks* stale to me. At the very least,
`TypeCheckDiagnostic` no longer exists, so that would need to be fixed.
And it doesn't really make sense to me (at this point) to make
`Diagnostic` a Salsa struct, particularly since we are keen on using it
in Ruff (at some point).
We do keep around `OldSecondaryDiagnosticMessage`, since that's part of
the Red Knot `InferContext` API. But it's a rather simple type, and
we'll be able to delete it entirely once `InferContext` exposes the new
`Diagnostic` type directly.
Since we aren't consuming `OldSecondaryDiagnosticMessage` any more, we
can now accept a slice instead of a vec. (Thanks Clippy.)
This replaces things like `TypeCheckDiagnostic` with the new Diagnostic`
type.
This is a "surgical" replacement where we retain the existing API of
of diagnostic reporting such that _most_ of Red Knot doesn't need to be
changed to support this update. But it will enable us to start using the
new diagnostic renderer and to delete the old renderer. It also paves
the path for exposing the new `Diagnostic` data model to the broader Red
Knot codebase.
I did this mostly because it wasn't buying us much, and I'm
trying to simplify the public API of the types I'd like to
refactor in order to make the refactor simpler.
If we really want something like this, we can re-add it
later.
I removed this to see how much code was depending internally on the
`&[Arc<TypeCheckDiagnostic>]` representation. Thankfully, it was just
one place. So I just removed the `Deref` impl in favor of adding an
explicit `iter` method.
In general, I think using `Deref` for things like this is _somewhat_ of
an abuse. The tip-off is if there are `&self` or `&mut self` methods on
the type, then it's probably not a good candidate for `Deref`.
## Summary
Implement basic *Goto type definition* support for Red Knot's LSP.
This PR also builds the foundation for other LSP operations. E.g., Goto
definition, hover, etc., should be able to reuse some, if not most,
logic introduced in this PR.
The basic steps of resolving the type definitions are:
1. Find the closest token for the cursor offset. This is a bit more
subtle than I first anticipated because the cursor could be positioned
right between the callee and the `(` in `call(test)`, in which case we
want to resolve the type for `call`.
2. Find the node with the minimal range that fully encloses the token
found in 1. I somewhat suspect that 1 and 2 could be done at the same
time but it complicated things because we also need to compute the spine
(ancestor chain) for the node and there's no guarantee that the found
nodes have the same ancestors
3. Reduce the node found in 2. to a node that is a valid goto target.
This may require traversing upwards to e.g. find the closest expression.
4. Resolve the type for the goto target
5. Resolve the location for the type, return it to the LSP
## Design decisions
The current implementation navigates to the inferred type. I think this
is what we want because it means that it correctly accounts for
narrowing (in which case we want to go to the narrowed type because
that's the value's type at the given position). However, it does have
the downside that Goto type definition doesn't work whenever we infer `T
& Unknown` because intersection types aren't supported. I'm not sure
what to do about this specific case, other than maybe ignoring `Unkown`
in Goto type definition if the type is an intersection?
## Known limitations
* Types defined in the vendored typeshed aren't supported because the
client can't open files from the red knot binary (we can either
implement our own file protocol and handler OR extract the typeshed
files and point there). See
https://github.com/astral-sh/ruff/issues/17041
* Red Knot only exposes an API to get types for expressions and
definitions. However, there are many other nodes with identifiers that
can have a type (e.g. go to type of a globals statement, match patterns,
...). We can add support for those in separate PRs (after we figure out
how to query the types from the semantic model). See
https://github.com/astral-sh/ruff/issues/17113
* We should have a higher-level API for the LSP that doesn't directly
call semantic queries. I intentionally decided not to design that API
just yet.
## Test plan
https://github.com/user-attachments/assets/fa077297-a42d-4ec8-b71f-90c0802b4edb
Goto type definition on a union
<img width="1215" alt="Screenshot 2025-04-01 at 13 02 55"
src="https://github.com/user-attachments/assets/689cabcc-4a86-4a18-b14a-c56f56868085"
/>
Note: I recorded this using a custom typeshed path so that navigating to
builtins works.
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## Summary
from https://github.com/astral-sh/ruff/pull/17034#discussion_r2024222525
This is a simple PR to fix the invalid behavior of `NotImplemented` on
Python >=3.10.
## Test Plan
I think it would be better if we could run mdtest across multiple Python
versions in GitHub Actions.
<!-- How was it tested? -->
---------
Co-authored-by: David Peter <sharkdp@users.noreply.github.com>
## Summary
Add support for decorators on function as well as support
for properties by adding special handling for `@property` and `@<name of
property>.setter`/`.getter` decorators.
closes https://github.com/astral-sh/ruff/issues/16987
## Ecosystem results
- ✔️ A lot of false positives are fixed by our new
understanding of properties
- 🔴 A bunch of new false positives (typically
`possibly-unbound-attribute` or `invalid-argument-type`) occur because
we currently do not perform type narrowing on attributes. And with the
new understanding of properties, this becomes even more relevant. In
many cases, the narrowing occurs through an assertion, so this is also
something that we need to implement to get rid of these false positives.
- 🔴 A few new false positives occur because we do not
understand generics, and therefore some calls to custom setters fail.
- 🔴 Similarly, some false positives occur because we do not
understand protocols yet.
- ✔️ Seems like a true positive to me. [The
setter](e624d8edfa/src/packaging/specifiers.py (L752-L754))
only accepts `bools`, but `None` is assigned in [this
line](e624d8edfa/tests/test_specifiers.py (L688)).
```
+ error[lint:invalid-assignment]
/tmp/mypy_primer/projects/packaging/tests/test_specifiers.py:688:9:
Invalid assignment to data descriptor attribute `prereleases` on type
`SpecifierSet` with custom `__set__` method
```
- ✔️ This is arguable also a true positive. The setter
[here](0c6c75644f/rich/table.py (L359-L363))
returns `Table`, but typeshed wants [setters to return
`None`](bf8d2a9912/stdlib/builtins.pyi (L1298)).
```
+ error[lint:invalid-argument-type]
/tmp/mypy_primer/projects/rich/rich/table.py:359:5: Object of type
`Literal[padding]` cannot be assigned to parameter 2 (`fset`) of bound
method `setter`; expected type `(Any, Any, /) -> None`
```
## Follow ups
- Fix the `@no_type_check` regression
- Implement class decorators
## Test Plan
New Markdown test suites for decorators and properties.
## Summary
Part of #15382, this PR adds property tests for callable types.
Specifically, this PR updates the property tests to generate an
arbitrary signature for a general callable type which includes:
* Arbitrary combination of parameter kinds in the correct order
* Arbitrary number of parameters
* Arbitrary optional types for annotation and return type
* Arbitrary parameter names (no duplicate names), optional for
positional-only parameters
## Test Plan
```
QUICKCHECK_TESTS=100000 cargo test -p red_knot_python_semantic -- --ignored types::property_tests::stable
```
Also, the commands in CI:
d72b4100a3/.github/workflows/daily_property_tests.yaml (L47-L52)
## Summary
Part of #15382, this PR adds support for disjointness between two
callable types. They are never disjoint because there exists a callable
type that's a subtype of all other callable types:
```py
(*args: object, **kwargs: object) -> Never
```
The `Never` is a subtype of every fully static type thus a callable type
that has the return type of `Never` means that it is a subtype of every
return type.
## Test Plan
Add test cases related to mixed parameter kinds, gradual form (`...`)
and `Never` type.
## Summary
Currently our `Type::Callable` wraps a four-variant `CallableType` enum.
But as time has gone on, I think we've found that the four variants in
`CallableType` are really more different to each other than they are
similar to each other:
- `GeneralCallableType` is a structural type describing all callable
types with a certain signature, but the other three types are "literal
types", more similar to the `FunctionLiteral` variant
- `GeneralCallableType` is not a singleton or a single-valued type, but
the other three are all single-valued types
(`WrapperDescriptorDunderGet` is even a singleton type)
- `GeneralCallableType` has (or should have) ambiguous truthiness, but
all possible inhabitants of the other three types are always truthy.
- As a structural type, `GeneralCallableType` can contain inner unions
and intersections that must be sorted in some contexts in our internal
model, but this is not true for the other three variants.
This PR flattens `Type::Callable` into four distinct `Type::` variants.
In the process, it fixes a number of latent bugs that were concealed by
the current architecture but are laid bare by the refactor. Unit tests
for these bugs are included in the PR.
## Summary
Currently if I run `uv run crates/red_knot_python_semantic/mdtest.py`
from the Ruff repo root, I get this output:
```
~/dev/ruff (main)⚡ % uv run crates/red_knot_python_semantic/mdtest.py
Ready to watch for changes...
```
...And I then have to make some spurious whitespace changes or something
to a test file in order to get the script to actually run mdtest. This
PR changes mdtest.py so that it does an initial run of all mdtests when
you invoke the script, and _then_ starts watching for changes in test
files/Rust code.
## Summary
This PR fixes a bug in callable subtyping to consider both the
positional and keyword form of the standard parameter in the supertype
when matching against variadic, keyword-only and keyword-variadic
parameter in the subtype.
This is done by collecting the unmatched standard parameters and then
checking them against the keyword-only / keyword-variadic parameters
after the positional loop.
## Test Plan
Add test cases.
## Summary
There are quite a few places we infer `Todo` types currently, and some
of them are nested somewhat deeply in type expressions. These can cause
spurious issues for the new `redundant-cast` diagnostics. We fixed all
the false positives we saw in the mypy_primer report before merging
https://github.com/astral-sh/ruff/pull/17100, but I think there are
still lots of places where we'd emit false positives due to this check
-- we currently don't run on that many projects at all in our
mypy_primer check:
d0c8eaa092/.github/workflows/mypy_primer.yaml (L71)
This PR fixes some more false positives from this diagnostic by making
the `Type::contains_todo()` method more expansive.
## Test Plan
I added a regression test which causes us to emit a spurious diagnostic
on `main`, but does not with this PR.
## Summary
In https://github.com/python/typeshed/pull/13520 the typeshed definition
of `typing.Any` was changed from `Any = object()` to `class Any: ...`.
Our automated typeshed updater pulled down this change in
https://github.com/astral-sh/ruff/pull/17106, with the consequence that
we no longer understand `Any`, which is... not good.
This PR gives us the ability to understand `Any` defined as a class
instead of `object()`. It doesn't remove our ability to understand the
old form. Perhaps at some point we'll want to remove it, but for now we
may as well support both old and new typeshed?
This also directly patches typeshed to use the new form of `Any`; this
is purely to work around our tests that no known class is inferred as
`Unknown`, which otherwise fail with the old typeshed and the changes in
this PR. (All other tests pass.) This patch to typeshed will shortly be
subsumed by https://github.com/astral-sh/ruff/pull/17106 anyway.
## Test Plan
Without the typeshed change in this PR, all tests pass except for the
two `known_class_doesnt_fallback_to_unknown_unexpectedly_*` tests (so we
still support the old form of defining `Any`). With the typeshed change
in this PR, all tests pass, so we now support the new form in a way that
is indistinguishable to our test suite from the old form. And
indistinguishable to the ecosystem check: after rebasing
https://github.com/astral-sh/ruff/pull/17106 on this PR, there's zero
ecosystem impact.
## Summary
I noticed we were inferring `Todo` as the declared type for annotations
such as `x: tuple[list[int], list[int]]`. This PR reworks our annotation
parsing so that we instead infer `tuple[Todo, Todo]` for this
annotation, which is quite a bit more precise.
## Test Plan
Existing mdtest updated.
## Summary
Following up from earlier discussion on Discord, this PR adds logic to
flag casts as redundant when the inferred type of the expression is the
same as the target type. It should follow the semantics from
[mypy](https://github.com/python/mypy/pull/1705).
Example:
```python
def f() -> int:
return 10
# error: [redundant-cast] "Value is already of type `int`"
cast(int, f())
```
## Summary
Part of #13694
Seems there a bit more to cover regarding `in` and other types, but i
can cover them in different PRs
## Test Plan
Add `in.md` file in narrowing conditionals folder
---------
Co-authored-by: Carl Meyer <carl@astral.sh>
## Summary
Rewrites the virtual env discovery to:
* Only use of `System` APIs, this ensures that the discovery will also
work when using a memory file system (testing or WASM)
* Don't traverse ancestor directories. We're not convinced that this is
necessary. Let's wait until someone shows us a use case where it is
needed
* Start from the project root and not from the current working
directory. This ensures that Red Knot picks up the right venv even when
using `knot --project ../other-dir`
## Test Plan
Existing tests, @ntBre tested that the `file_watching` tests no longer
pick up his virtual env in a parent directory
## Summary
In preparation for #17017, where we will need them to suppress new false
positives (once we understand the `ParamSpec.args`/`ParamSpec.kwargs`
properties).
## Test Plan
Tested on branch #17017
## Summary
Disallow empty `todo_type!()`s without a custom message. They can lead
to spurious diffs in `mypy_primer` where the only thing that's changed
is the file/line information.
## Summary
A quick fix for how union/intersection member search ins performed in
Knot.
## Test Plan
* Added a dunder method call test for Union, which exhibits the error
* Also added an intersection error, but it is not triggering currently
due to `call` logic not being fully implemented for intersections.
---------
Co-authored-by: David Peter <mail@david-peter.de>
## Summary
Closes#16661
This PR includes two changes:
- `NotImplementedType` is now a member of `KnownClass`
- We skip `is_assignable_to` checks for `NotImplemented` when checking
return types
### Limitation
```py
def f(cond: bool) -> int:
return 1 if cond else NotImplemented
```
The implementation covers cases where `NotImplemented` appears inside a
`Union`.
However, for more complex types (ex. `Intersection`) it will not worked.
In my opinion, supporting such complexity is unnecessary at this point.
## Test Plan
Two `mdtest` files were updated:
- `mdtest/function/return_type.md`
- `mdtest/type_properties/is_singleton.md`
To test `KnownClass`, run:
```bash
cargo test -p red_knot_python_semantic -- types::class::
```
