Make CallArguments salsa::interned

crates/red_knot_python_semantic/resources/mdtest/annotations/literal_string.md

@@ -73,12 +73,12 @@ qux = (foo, bar)
 reveal_type(qux)  # revealed: tuple[Literal["foo"], Literal["bar"]]
 
 # TODO: Infer "LiteralString"
-reveal_type(foo.join(qux))  # revealed: @Todo(Attribute access on `StringLiteral` types)
+reveal_type(foo.join(qux))  # revealed: @Todo(decorated method)
 
 template: LiteralString = "{}, {}"
 reveal_type(template)  # revealed: Literal["{}, {}"]
 # TODO: Infer `LiteralString`
-reveal_type(template.format(foo, bar))  # revealed: @Todo(Attribute access on `StringLiteral` types)
+reveal_type(template.format(foo, bar))  # revealed: @Todo(decorated method)
 ```
 
 ### Assignability

crates/red_knot_python_semantic/resources/mdtest/attributes.md

@@ -1005,8 +1005,8 @@ reveal_type(f.__kwdefaults__)  # revealed: @Todo(generics) | None
 Some attributes are special-cased, however:
 
 ```py
-reveal_type(f.__get__)  # revealed: @Todo(`__get__` method on functions)
-reveal_type(f.__call__)  # revealed: @Todo(`__call__` method on functions)
+reveal_type(f.__get__)  # revealed: <method-wrapper `__get__` of `f`>
+reveal_type(f.__call__)  # revealed: <bound method `__call__` of `Literal[f]`>
 ```
 
 ### Int-literal attributes
@@ -1015,7 +1015,7 @@ Most attribute accesses on int-literal types are delegated to `builtins.int`, si
 integers are instances of that class:
 
 ```py
-reveal_type((2).bit_length)  # revealed: @Todo(bound method)
+reveal_type((2).bit_length)  # revealed: <bound method `bit_length` of `Literal[2]`>
 reveal_type((2).denominator)  # revealed: @Todo(@property)
 ```
 
@@ -1029,11 +1029,11 @@ reveal_type((2).real)  # revealed: Literal[2]
 ### Bool-literal attributes
 
 Most attribute accesses on bool-literal types are delegated to `builtins.bool`, since all literal
-bols are instances of that class:
+bools are instances of that class:
 
 ```py
-reveal_type(True.__and__)  # revealed: @Todo(bound method)
-reveal_type(False.__or__)  # revealed: @Todo(bound method)
+reveal_type(True.__and__)  # revealed: @Todo(decorated method)
+reveal_type(False.__or__)  # revealed: @Todo(decorated method)
 ```
 
 Some attributes are special-cased, however:
@@ -1045,11 +1045,11 @@ reveal_type(False.real)  # revealed: Literal[0]
 
 ### Bytes-literal attributes
 
-All attribute access on literal `bytes` types is currently delegated to `buitins.bytes`:
+All attribute access on literal `bytes` types is currently delegated to `builtins.bytes`:
 
 ```py
-reveal_type(b"foo".join)  # revealed: @Todo(bound method)
-reveal_type(b"foo".endswith)  # revealed: @Todo(bound method)
+reveal_type(b"foo".join)  # revealed: <bound method `join` of `Literal[b"foo"]`>
+reveal_type(b"foo".endswith)  # revealed: <bound method `endswith` of `Literal[b"foo"]`>
 ```
 
 ## Instance attribute edge cases
@@ -1136,6 +1136,40 @@ class C:
 reveal_type(C().x)  # revealed: Unknown
 ```
 
+### Builtin types attributes
+
+This test can probably be removed eventually, but we currently include it because we do not yet
+understand generic bases and protocols, and we want to make sure that we can still use builtin types
+in our tests in the meantime. See the corresponding TODO in `Type::static_member` for more
+information.
+
+```py
+class C:
+    a_int: int = 1
+    a_str: str = "a"
+    a_bytes: bytes = b"a"
+    a_bool: bool = True
+    a_float: float = 1.0
+    a_complex: complex = 1 + 1j
+    a_tuple: tuple[int] = (1,)
+    a_range: range = range(1)
+    a_slice: slice = slice(1)
+    a_type: type = int
+    a_none: None = None
+
+reveal_type(C.a_int)  # revealed: int
+reveal_type(C.a_str)  # revealed: str
+reveal_type(C.a_bytes)  # revealed: bytes
+reveal_type(C.a_bool)  # revealed: bool
+reveal_type(C.a_float)  # revealed: int | float
+reveal_type(C.a_complex)  # revealed: int | float | complex
+reveal_type(C.a_tuple)  # revealed: tuple[int]
+reveal_type(C.a_range)  # revealed: range
+reveal_type(C.a_slice)  # revealed: slice
+reveal_type(C.a_type)  # revealed: type
+reveal_type(C.a_none)  # revealed: None
+```
+
 ## References
 
 Some of the tests in the *Class and instance variables* section draw inspiration from

crates/red_knot_python_semantic/resources/mdtest/call/getattr_static.md

@@ -0,0 +1,133 @@
+# `inspect.getattr_static`
+
+## Basic usage
+
+`inspect.getattr_static` is a function that returns attributes of an object without invoking the
+descriptor protocol (for caveats, see the [official documentation]).
+
+Consider the following example:
+
+```py
+import inspect
+
+class Descriptor:
+    def __get__(self, instance, owner) -> str:
+        return 1
+
+class C:
+    normal: int = 1
+    descriptor: Descriptor = Descriptor()
+```
+
+If we access attributes on an instance of `C` as usual, the descriptor protocol is invoked, and we
+get a type of `str` for the `descriptor` attribute:
+
+```py
+c = C()
+
+reveal_type(c.normal)  # revealed: int
+reveal_type(c.descriptor)  # revealed: str
+```
+
+However, if we use `inspect.getattr_static`, we can see the underlying `Descriptor` type:
+
+```py
+reveal_type(inspect.getattr_static(c, "normal"))  # revealed: int
+reveal_type(inspect.getattr_static(c, "descriptor"))  # revealed: Descriptor
+```
+
+For non-existent attributes, a default value can be provided:
+
+```py
+reveal_type(inspect.getattr_static(C, "normal", "default-arg"))  # revealed: int
+reveal_type(inspect.getattr_static(C, "non_existent", "default-arg"))  # revealed: Literal["default-arg"]
+```
+
+When a non-existent attribute is accessed without a default value, the runtime raises an
+`AttributeError`. We could emit a diagnostic for this case, but that is currently not supported:
+
+```py
+# TODO: we could emit a diagnostic here
+reveal_type(inspect.getattr_static(C, "non_existent"))  # revealed: Never
+```
+
+We can access attributes on objects of all kinds:
+
+```py
+import sys
+
+reveal_type(inspect.getattr_static(sys, "platform"))  # revealed: LiteralString
+reveal_type(inspect.getattr_static(inspect, "getattr_static"))  # revealed: Literal[getattr_static]
+
+reveal_type(inspect.getattr_static(1, "real"))  # revealed: Literal[1]
+```
+
+(Implicit) instance attributes can also be accessed through `inspect.getattr_static`:
+
+```py
+class D:
+    def __init__(self) -> None:
+        self.instance_attr: int = 1
+
+reveal_type(inspect.getattr_static(D(), "instance_attr"))  # revealed: int
+```
+
+## Error cases
+
+We can only infer precise types if the attribute is a literal string. In all other cases, we fall
+back to `Any`:
+
+```py
+import inspect
+
+class C:
+    x: int = 1
+
+def _(attr_name: str):
+    reveal_type(inspect.getattr_static(C(), attr_name))  # revealed: Any
+    reveal_type(inspect.getattr_static(C(), attr_name, 1))  # revealed: Any
+```
+
+But we still detect errors in the number or type of arguments:
+
+```py
+# error: [missing-argument] "No arguments provided for required parameters `obj`, `attr` of function `getattr_static`"
+inspect.getattr_static()
+
+# error: [missing-argument] "No argument provided for required parameter `attr`"
+inspect.getattr_static(C())
+
+# error: [invalid-argument-type] "Object of type `Literal[1]` cannot be assigned to parameter 2 (`attr`) of function `getattr_static`; expected type `str`"
+inspect.getattr_static(C(), 1)
+
+# error: [too-many-positional-arguments] "Too many positional arguments to function `getattr_static`: expected 3, got 4"
+inspect.getattr_static(C(), "x", "default-arg", "one too many")
+```
+
+## Possibly unbound attributes
+
+```py
+import inspect
+
+def _(flag: bool):
+    class C:
+        if flag:
+            x: int = 1
+
+    reveal_type(inspect.getattr_static(C, "x", "default"))  # revealed: int | Literal["default"]
+```
+
+## Gradual types
+
+```py
+import inspect
+from typing import Any
+
+def _(a: Any, tuple_of_any: tuple[Any]):
+    reveal_type(inspect.getattr_static(a, "x", "default"))  # revealed: Any | Literal["default"]
+
+    # TODO: Ideally, this would just be `Literal[index]`
+    reveal_type(inspect.getattr_static(tuple_of_any, "index", "default"))  # revealed: Literal[index] | Literal["default"]
+```
+
+[official documentation]: https://docs.python.org/3/library/inspect.html#inspect.getattr_static

crates/red_knot_python_semantic/resources/mdtest/call/methods.md

@@ -0,0 +1,258 @@
+# Methods
+
+## Background: Functions as descriptors
+
+> Note: See also this related section in the descriptor guide: [Functions and methods].
+
+Say we have a simple class `C` with a function definition `f` inside its body:
+
+```py
+class C:
+    def f(self, x: int) -> str:
+        return "a"
+```
+
+Whenever we access the `f` attribute through the class object itself (`C.f`) or through an instance
+(`C().f`), this access happens via the descriptor protocol. Functions are (non-data) descriptors
+because they implement a `__get__` method. This is crucial in making sure that method calls work as
+expected. In general, the signature of the `__get__` method in the descriptor protocol is
+`__get__(self, instance, owner)`. The `self` argument is the descriptor object itself (`f`). The
+passed value for the `instance` argument depends on whether the attribute is accessed from the class
+object (in which case it is `None`), or from an instance (in which case it is the instance of type
+`C`). The `owner` argument is the class itself (`C` of type `Literal[C]`). To summarize:
+
+- `C.f` is equivalent to `getattr_static(C, "f").__get__(None, C)`
+- `C().f` is equivalent to `getattr_static(C, "f").__get__(C(), C)`
+
+Here, `inspect.getattr_static` is used to bypass the descriptor protocol and directly access the
+function attribute. The way the special `__get__` method *on functions* works is as follows. In the
+former case, if the `instance` argument is `None`, `__get__` simply returns the function itself. In
+the latter case, it returns a *bound method* object:
+
+```py
+from inspect import getattr_static
+
+reveal_type(getattr_static(C, "f"))  # revealed: Literal[f]
+
+reveal_type(getattr_static(C, "f").__get__)  # revealed: <method-wrapper `__get__` of `f`>
+
+reveal_type(getattr_static(C, "f").__get__(None, C))  # revealed: Literal[f]
+reveal_type(getattr_static(C, "f").__get__(C(), C))  # revealed: <bound method `f` of `C`>
+```
+
+In conclusion, this is why we see the following two types when accessing the `f` attribute on the
+class object `C` and on an instance `C()`:
+
+```py
+reveal_type(C.f)  # revealed: Literal[f]
+reveal_type(C().f)  # revealed: <bound method `f` of `C`>
+```
+
+A bound method is a callable object that contains a reference to the `instance` that it was called
+on (can be inspected via `__self__`), and the function object that it refers to (can be inspected
+via `__func__`):
+
+```py
+bound_method = C().f
+
+reveal_type(bound_method.__self__)  # revealed: C
+reveal_type(bound_method.__func__)  # revealed: Literal[f]
+```
+
+When we call the bound method, the `instance` is implicitly passed as the first argument (`self`):
+
+```py
+reveal_type(C().f(1))  # revealed: str
+reveal_type(bound_method(1))  # revealed: str
+```
+
+When we call the function object itself, we need to pass the `instance` explicitly:
+
+```py
+C.f(1)  # error: [missing-argument]
+
+reveal_type(C.f(C(), 1))  # revealed: str
+```
+
+When we access methods from derived classes, they will be bound to instances of the derived class:
+
+```py
+class D(C):
+    pass
+
+reveal_type(D().f)  # revealed: <bound method `f` of `D`>
+```
+
+If we access an attribute on a bound method object itself, it will defer to `types.MethodType`:
+
+```py
+reveal_type(bound_method.__hash__)  # revealed: <bound method `__hash__` of `MethodType`>
+```
+
+If an attribute is not available on the bound method object, it will be looked up on the underlying
+function object. We model this explicitly, which means that we can access `__kwdefaults__` on bound
+methods, even though it is not available on `types.MethodType`:
+
+```py
+reveal_type(bound_method.__kwdefaults__)  # revealed: @Todo(generics) | None
+```
+
+## Basic method calls on class objects and instances
+
+```py
+class Base:
+    def method_on_base(self, x: int | None) -> str:
+        return "a"
+
+class Derived(Base):
+    def method_on_derived(self, x: bytes) -> tuple[int, str]:
+        return (1, "a")
+
+reveal_type(Base().method_on_base(1))  # revealed: str
+reveal_type(Base.method_on_base(Base(), 1))  # revealed: str
+
+Base().method_on_base("incorrect")  # error: [invalid-argument-type]
+Base().method_on_base()  # error: [missing-argument]
+Base().method_on_base(1, 2)  # error: [too-many-positional-arguments]
+
+reveal_type(Derived().method_on_base(1))  # revealed: str
+reveal_type(Derived().method_on_derived(b"abc"))  # revealed: tuple[int, str]
+reveal_type(Derived.method_on_base(Derived(), 1))  # revealed: str
+reveal_type(Derived.method_on_derived(Derived(), b"abc"))  # revealed: tuple[int, str]
+```
+
+## Method calls on literals
+
+### Boolean literals
+
+```py
+reveal_type(True.bit_length())  # revealed: int
+reveal_type(True.as_integer_ratio())  # revealed: tuple[int, Literal[1]]
+```
+
+### Integer literals
+
+```py
+reveal_type((42).bit_length())  # revealed: int
+```
+
+### String literals
+
+```py
+reveal_type("abcde".find("abc"))  # revealed: int
+reveal_type("foo".encode(encoding="utf-8"))  # revealed: bytes
+
+"abcde".find(123)  # error: [invalid-argument-type]
+```
+
+### Bytes literals
+
+```py
+reveal_type(b"abcde".startswith(b"abc"))  # revealed: bool
+```
+
+## Method calls on `LiteralString`
+
+```py
+from typing_extensions import LiteralString
+
+def f(s: LiteralString) -> None:
+    reveal_type(s.find("a"))  # revealed: int
+```
+
+## Method calls on `tuple`
+
+```py
+def f(t: tuple[int, str]) -> None:
+    reveal_type(t.index("a"))  # revealed: int
+```
+
+## Method calls on unions
+
+```py
+from typing import Any
+
+class A:
+    def f(self) -> int:
+        return 1
+
+class B:
+    def f(self) -> str:
+        return "a"
+
+def f(a_or_b: A | B, any_or_a: Any | A):
+    reveal_type(a_or_b.f)  # revealed: <bound method `f` of `A`> | <bound method `f` of `B`>
+    reveal_type(a_or_b.f())  # revealed: int | str
+
+    reveal_type(any_or_a.f)  # revealed: Any | <bound method `f` of `A`>
+    reveal_type(any_or_a.f())  # revealed: Any | int
+```
+
+## Method calls on `KnownInstance` types
+
+```toml
+[environment]
+python-version = "3.12"
+```
+
+```py
+type IntOrStr = int | str
+
+reveal_type(IntOrStr.__or__)  # revealed: <bound method `__or__` of `typing.TypeAliasType`>
+```
+
+## Error cases: Calling `__get__` for methods
+
+The `__get__` method on `types.FunctionType` has the following overloaded signature in typeshed:
+
+```py
+from types import FunctionType, MethodType
+from typing import overload
+
+@overload
+def __get__(self, instance: None, owner: type, /) -> FunctionType: ...
+@overload
+def __get__(self, instance: object, owner: type | None = None, /) -> MethodType: ...
+```
+
+Here, we test that this signature is enforced correctly:
+
+```py
+from inspect import getattr_static
+
+class C:
+    def f(self, x: int) -> str:
+        return "a"
+
+method_wrapper = getattr_static(C, "f").__get__
+
+reveal_type(method_wrapper)  # revealed: <method-wrapper `__get__` of `f`>
+
+# All of these are fine:
+method_wrapper(C(), C)
+method_wrapper(C())
+method_wrapper(C(), None)
+method_wrapper(None, C)
+
+# Passing `None` without an `owner` argument is an
+# error: [missing-argument] "No argument provided for required parameter `owner`"
+method_wrapper(None)
+
+# Passing something that is not assignable to `type` as the `owner` argument is an
+# error: [invalid-argument-type] "Object of type `Literal[1]` cannot be assigned to parameter 2 (`owner`); expected type `type`"
+method_wrapper(None, 1)
+
+# Passing `None` as the `owner` argument when `instance` is `None` is an
+# error: [invalid-argument-type] "Object of type `None` cannot be assigned to parameter 2 (`owner`); expected type `type`"
+method_wrapper(None, None)
+
+# Calling `__get__` without any arguments is an
+# error: [missing-argument] "No argument provided for required parameter `instance`"
+method_wrapper()
+
+# Calling `__get__` with too many positional arguments is an
+# error: [too-many-positional-arguments] "Too many positional arguments: expected 2, got 3"
+method_wrapper(C(), C, "one too many")
+```
+
+[functions and methods]: https://docs.python.org/3/howto/descriptor.html#functions-and-methods

crates/red_knot_python_semantic/resources/mdtest/descriptor_protocol.md

@@ -22,22 +22,26 @@ class Ten:
         pass
 
 class C:
-    ten = Ten()
+    ten: Ten = Ten()
 
 c = C()
 
-# TODO: this should be `Literal[10]`
-reveal_type(c.ten)  # revealed: Unknown | Ten
+reveal_type(c.ten)  # revealed: Literal[10]
 
-# TODO: This should `Literal[10]`
-reveal_type(C.ten)  # revealed: Unknown | Ten
+reveal_type(C.ten)  # revealed: Literal[10]
 
 # These are fine:
-c.ten = 10
+# TODO: This should not be an error
+c.ten = 10  # error: [invalid-assignment]
 C.ten = 10
 
-# TODO: Both of these should be errors
+# TODO: This should be an error (as the wrong type is being implicitly passed to `Ten.__set__`),
+# but the error message is misleading.
+# error: [invalid-assignment] "Object of type `Literal[11]` is not assignable to attribute `ten` of type `Ten`"
 c.ten = 11
+
+# TODO: same as above
+# error: [invalid-assignment] "Object of type `Literal[11]` is not assignable to attribute `ten` of type `Literal[10]`"
 C.ten = 11
 ```
 
@@ -57,24 +61,86 @@ class FlexibleInt:
         self._value = int(value)
 
 class C:
-    flexible_int = FlexibleInt()
+    flexible_int: FlexibleInt = FlexibleInt()
 
 c = C()
 
-# TODO: should be `int | None`
-reveal_type(c.flexible_int)  # revealed: Unknown | FlexibleInt
+reveal_type(c.flexible_int)  # revealed: int | None
 
+# TODO: These should not be errors
+# error: [invalid-assignment]
 c.flexible_int = 42  # okay
+# error: [invalid-assignment]
 c.flexible_int = "42"  # also okay!
 
-# TODO: should be `int | None`
-reveal_type(c.flexible_int)  # revealed: Unknown | FlexibleInt
+reveal_type(c.flexible_int)  # revealed: int | None
 
-# TODO: should be an error
+# TODO: This should be an error, but the message needs to be improved.
+# error: [invalid-assignment] "Object of type `None` is not assignable to attribute `flexible_int` of type `FlexibleInt`"
 c.flexible_int = None  # not okay
 
-# TODO: should be `int | None`
-reveal_type(c.flexible_int)  # revealed: Unknown | FlexibleInt
+reveal_type(c.flexible_int)  # revealed: int | None
+```
+
+## Data and non-data descriptors
+
+Descriptors that define `__set__` or `__delete__` are called *data descriptors*. An example\
+of a data descriptor is a `property` with a setter and/or a deleter.\
+Descriptors that only define `__get__`, meanwhile, are called *non-data descriptors*. Examples
+include\
+functions, `classmethod` or `staticmethod`).
+
+The precedence chain for attribute access is (1) data descriptors, (2) instance attributes, and (3)
+non-data descriptors.
+
+```py
+from typing import Literal
+
+class DataDescriptor:
+    def __get__(self, instance: object, owner: type | None = None) -> Literal["data"]:
+        return "data"
+
+    def __set__(self, instance: int, value) -> None:
+        pass
+
+class NonDataDescriptor:
+    def __get__(self, instance: object, owner: type | None = None) -> Literal["non-data"]:
+        return "non-data"
+
+class C:
+    data_descriptor = DataDescriptor()
+    non_data_descriptor = NonDataDescriptor()
+
+    def f(self):
+        # This explains why data descriptors come first in the precedence chain. If
+        # instance attributes would take priority, we would override the descriptor
+        # here. Instead, this calls `DataDescriptor.__set__`, i.e. it does not affect
+        # the type of the `data_descriptor` attribute.
+        self.data_descriptor = 1
+
+        # However, for non-data descriptors, instance attributes do take precedence.
+        # So it is possible to override them.
+        self.non_data_descriptor = 1
+
+c = C()
+
+# TODO: This should ideally be `Unknown | Literal["data"]`.
+#
+#     - Pyright also wrongly shows `int | Literal['data']` here
+#     - Mypy shows Literal["data"] here, but also shows Literal["non-data"] below.
+#
+reveal_type(c.data_descriptor)  # revealed: Unknown | Literal["data", 1]
+
+reveal_type(c.non_data_descriptor)  # revealed: Unknown | Literal["non-data", 1]
+
+reveal_type(C.data_descriptor)  # revealed: Unknown | Literal["data"]
+
+reveal_type(C.non_data_descriptor)  # revealed: Unknown | Literal["non-data"]
+
+# It is possible to override data descriptors via class objects. The following
+# assignment does not call `DataDescriptor.__set__`. For this reason, we infer
+# `Unknown | …` for all (descriptor) attributes.
+C.data_descriptor = "something else"  # This is okay
 ```
 
 ## Built-in `property` descriptor
@@ -101,7 +167,7 @@ c = C()
 reveal_type(c._name)  # revealed: str | None
 
 # Should be `str`
-reveal_type(c.name)  # revealed: @Todo(bound method)
+reveal_type(c.name)  # revealed: @Todo(decorated method)
 
 # Should be `builtins.property`
 reveal_type(C.name)  # revealed: Literal[name]
@@ -142,7 +208,7 @@ reveal_type(c1)  # revealed: @Todo(return type)
 reveal_type(C.get_name())  # revealed: @Todo(return type)
 
 # TODO: should be `str`
-reveal_type(C("42").get_name())  # revealed: @Todo(bound method)
+reveal_type(C("42").get_name())  # revealed: @Todo(decorated method)
 ```
 
 ## Descriptors only work when used as class variables
@@ -160,9 +226,10 @@ class Ten:
 
 class C:
     def __init__(self):
-        self.ten = Ten()
+        self.ten: Ten = Ten()
 
-reveal_type(C().ten)  # revealed: Unknown | Ten
+# TODO: Should be Ten
+reveal_type(C().ten)  # revealed: Literal[10]
 ```
 
 ## Descriptors distinguishing between class and instance access
@@ -186,13 +253,166 @@ class Descriptor:
             return "called on class object"
 
 class C:
-    d = Descriptor()
+    d: Descriptor = Descriptor()
 
 # TODO: should be `Literal["called on class object"]
-reveal_type(C.d)  # revealed: Unknown | Descriptor
+reveal_type(C.d)  # revealed: LiteralString
 
 # TODO: should be `Literal["called on instance"]
-reveal_type(C().d)  # revealed: Unknown | Descriptor
+reveal_type(C().d)  # revealed: LiteralString
+```
+
+## Undeclared descriptor arguments
+
+If a descriptor attribute is not declared, we union with `Unknown`, just like for regular
+attributes, since that attribute could be overwritten externally. Even a data descriptor with a
+`__set__` method can be overwritten when accessed through a class object.
+
+```py
+class Descriptor:
+    def __get__(self, instance: object, owner: type | None = None) -> int:
+        return 1
+
+    def __set__(self, instance: object, value: int) -> None:
+        pass
+
+class C:
+    descriptor = Descriptor()
+
+C.descriptor = "something else"
+
+# This could also be `Literal["something else"]` if we support narrowing of attribute types based on assignments
+reveal_type(C.descriptor)  # revealed: Unknown | int
+```
+
+## Descriptors with incorrect `__get__` signature
+
+```py
+class Descriptor:
+    # `__get__` method with missing parameters:
+    def __get__(self) -> int:
+        return 1
+
+class C:
+    descriptor: Descriptor = Descriptor()
+
+# TODO: This should be an error
+reveal_type(C.descriptor)  # revealed: Descriptor
+```
+
+## Possibly-unbound `__get__` method
+
+```py
+def _(flag: bool):
+    class MaybeDescriptor:
+        if flag:
+            def __get__(self, instance: object, owner: type | None = None) -> int:
+                return 1
+
+    class C:
+        descriptor: MaybeDescriptor = MaybeDescriptor()
+
+    # TODO: This should be `MaybeDescriptor | int`
+    reveal_type(C.descriptor)  # revealed: int
+```
+
+## Dunder methods
+
+Dunder methods are looked up on the meta type, but we still need to invoke the descriptor protocol:
+
+```py
+class SomeCallable:
+    def __call__(self, x: int) -> str:
+        return "a"
+
+class Descriptor:
+    def __get__(self, instance: object, owner: type | None = None) -> SomeCallable:
+        return SomeCallable()
+
+class B:
+    __call__: Descriptor = Descriptor()
+
+b_instance = B()
+reveal_type(b_instance(1))  # revealed: str
+
+b_instance("bla")  # error: [invalid-argument-type]
+```
+
+## Functions as descriptors
+
+Functions are descriptors because they implement a `__get__` method. This is crucial in making sure
+that method calls work as expected. See [this test suite](./call/methods.md) for more information.
+Here, we only demonstrate how `__get__` works on functions:
+
+```py
+from inspect import getattr_static
+
+def f(x: object) -> str:
+    return "a"
+
+reveal_type(f)  # revealed: Literal[f]
+reveal_type(f.__get__)  # revealed: <method-wrapper `__get__` of `f`>
+reveal_type(f.__get__(None, type(f)))  # revealed: Literal[f]
+reveal_type(f.__get__(None, type(f))(1))  # revealed: str
+
+wrapper_descriptor = getattr_static(f, "__get__")
+
+reveal_type(wrapper_descriptor)  # revealed: <wrapper-descriptor `__get__` of `function` objects>
+reveal_type(wrapper_descriptor(f, None, type(f)))  # revealed: Literal[f]
+
+# Attribute access on the method-wrapper `f.__get__` falls back to `MethodWrapperType`:
+reveal_type(f.__get__.__hash__)  # revealed: <bound method `__hash__` of `MethodWrapperType`>
+
+# Attribute access on the wrapper-descriptor falls back to `WrapperDescriptorType`:
+reveal_type(wrapper_descriptor.__qualname__)  # revealed: @Todo(@property)
+```
+
+We can also bind the free function `f` to an instance of a class `C`:
+
+```py
+class C: ...
+
+bound_method = wrapper_descriptor(f, C(), C)
+
+reveal_type(bound_method)  # revealed: <bound method `f` of `C`>
+```
+
+We can then call it, and the instance of `C` is implicitly passed to the first parameter of `f`
+(`x`):
+
+```py
+reveal_type(bound_method())  # revealed: str
+```
+
+Finally, we test some error cases for the call to the wrapper descriptor:
+
+```py
+# Calling the wrapper descriptor without any arguments is an
+# error: [missing-argument] "No arguments provided for required parameters `self`, `instance`"
+wrapper_descriptor()
+
+# Calling it without the `instance` argument is an also an
+# error: [missing-argument] "No argument provided for required parameter `instance`"
+wrapper_descriptor(f)
+
+# Calling it without the `owner` argument if `instance` is not `None` is an
+# error: [missing-argument] "No argument provided for required parameter `owner`"
+wrapper_descriptor(f, None)
+
+# But calling it with an instance is fine (in this case, the `owner` argument is optional):
+wrapper_descriptor(f, C())
+
+# Calling it with something that is not a `FunctionType` as the first argument is an
+# error: [invalid-argument-type] "Object of type `Literal[1]` cannot be assigned to parameter 1 (`self`); expected type `FunctionType`"
+wrapper_descriptor(1, None, type(f))
+
+# Calling it with something that is not a `type` as the `owner` argument is an
+# error: [invalid-argument-type] "Object of type `Literal[f]` cannot be assigned to parameter 3 (`owner`); expected type `type`"
+wrapper_descriptor(f, None, f)
+
+# Calling it with too many positional arguments is an
+# error: [too-many-positional-arguments] "Too many positional arguments: expected 3, got 4"
+wrapper_descriptor(f, None, type(f), "one too many")
 ```
 
 [descriptors]: https://docs.python.org/3/howto/descriptor.html

crates/red_knot_python_semantic/resources/mdtest/protocols.md

@@ -0,0 +1,15 @@
+# Protocols
+
+We do not support protocols yet, but to avoid false positives, we *partially* support some known
+protocols.
+
+## `typing.SupportsIndex`
+
+```py
+from typing import SupportsIndex, Literal
+
+def _(some_int: int, some_literal_int: Literal[1], some_indexable: SupportsIndex):
+    a: SupportsIndex = some_int
+    b: SupportsIndex = some_literal_int
+    c: SupportsIndex = some_indexable
+```

crates/red_knot_python_semantic/resources/mdtest/scopes/moduletype_attrs.md

@@ -9,7 +9,7 @@ is unbound.
 ```py
 reveal_type(__name__)  # revealed: str
 reveal_type(__file__)  # revealed: str | None
-reveal_type(__loader__)  # revealed: LoaderProtocol | None
+reveal_type(__loader__)  # revealed: @Todo(instance attribute on class with dynamic base) | None
 reveal_type(__package__)  # revealed: str | None
 reveal_type(__doc__)  # revealed: str | None
 
@@ -54,10 +54,10 @@ inside the module:
 import typing
 
 reveal_type(typing.__name__)  # revealed: str
-reveal_type(typing.__init__)  # revealed: @Todo(bound method)
+reveal_type(typing.__init__)  # revealed: <bound method `__init__` of `ModuleType`>
 
 # These come from `builtins.object`, not `types.ModuleType`:
-reveal_type(typing.__eq__)  # revealed: @Todo(bound method)
+reveal_type(typing.__eq__)  # revealed: <bound method `__eq__` of `ModuleType`>
 
 reveal_type(typing.__class__)  # revealed: Literal[ModuleType]
 

crates/red_knot_python_semantic/resources/mdtest/sys_platform.md

@@ -66,6 +66,6 @@ It is [recommended](https://docs.python.org/3/library/sys.html#sys.platform) to
 ```py
 import sys
 
-reveal_type(sys.platform.startswith("freebsd"))  # revealed: @Todo(Attribute access on `LiteralString` types)
-reveal_type(sys.platform.startswith("linux"))  # revealed: @Todo(Attribute access on `LiteralString` types)
+reveal_type(sys.platform.startswith("freebsd"))  # revealed: bool
+reveal_type(sys.platform.startswith("linux"))  # revealed: bool
 ```

crates/red_knot_python_semantic/resources/mdtest/type_of/dynamic.md

@@ -35,7 +35,7 @@ in strict mode.
 ```py
 def f(x: type):
     reveal_type(x)  # revealed: type
-    reveal_type(x.__repr__)  # revealed: @Todo(bound method)
+    reveal_type(x.__repr__)  # revealed: <bound method `__repr__` of `type`>
 
 class A: ...
 
@@ -50,7 +50,7 @@ x: type = A()  # error: [invalid-assignment]
 ```py
 def f(x: type[object]):
     reveal_type(x)  # revealed: type
-    reveal_type(x.__repr__)  # revealed: @Todo(bound method)
+    reveal_type(x.__repr__)  # revealed: <bound method `__repr__` of `type`>
 
 class A: ...
 

crates/red_knot_python_semantic/resources/mdtest/type_properties/truthiness.md

@@ -75,3 +75,19 @@ class Boom:
 
 reveal_type(bool(Boom()))  # revealed: bool
 ```
+
+### Possibly unbound __bool__ method
+
+```py
+from typing import Literal
+
+def flag() -> bool:
+    return True
+
+class PossiblyUnboundTrue:
+    if flag():
+        def __bool__(self) -> Literal[True]:
+            return True
+
+reveal_type(bool(PossiblyUnboundTrue()))  # revealed: bool
+```

crates/red_knot_python_semantic/src/module_resolver/module.rs

@@ -109,6 +109,7 @@ pub enum KnownModule {
     #[allow(dead_code)]
     Abc, // currently only used in tests
     Collections,
+    Inspect,
     KnotExtensions,
 }
 
@@ -123,6 +124,7 @@ impl KnownModule {
             Self::Sys => "sys",
             Self::Abc => "abc",
             Self::Collections => "collections",
+            Self::Inspect => "inspect",
             Self::KnotExtensions => "knot_extensions",
         }
     }
@@ -149,6 +151,7 @@ impl KnownModule {
             "sys" => Some(Self::Sys),
             "abc" => Some(Self::Abc),
             "collections" => Some(Self::Collections),
+            "inspect" => Some(Self::Inspect),
             "knot_extensions" => Some(Self::KnotExtensions),
             _ => None,
         }

crates/red_knot_python_semantic/src/types/call.rs

@@ -11,7 +11,7 @@ pub(super) use bind::{bind_call, CallBinding};
 /// A successfully bound call where all arguments are valid.
 ///
 /// It's guaranteed that the wrapped bindings have no errors.
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq, salsa::Update)]
 pub(super) enum CallOutcome<'db> {
     /// The call resolves to exactly one binding.
     Single(CallBinding<'db>),
@@ -84,7 +84,7 @@ impl<'db> CallOutcome<'db> {
 }
 
 /// The reason why calling a type failed.
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq, salsa::Update)]
 pub(super) enum CallError<'db> {
     /// The type is not callable.
     NotCallable {

crates/red_knot_python_semantic/src/types/call/arguments.rs

@@ -1,53 +1,60 @@
+use ruff_python_ast::name::Name;
+
+use crate::Db;
+
 use super::Type;
 
 /// Typed arguments for a single call, in source order.
-#[derive(Clone, Debug, Default)]
-pub(crate) struct CallArguments<'a, 'db>(Vec<Argument<'a, 'db>>);
+#[salsa::interned]
+pub(crate) struct CallArguments<'db> {
+    args: Vec<Argument<'db>>,
+}
+
+impl<'a, 'db> CallArguments<'db> {
+    /// Create a [`CallArguments`] with no arguments.
+    pub(crate) fn none(db: &'db dyn Db) -> Self {
+        CallArguments::new(db, Vec::new())
+    }
 
-impl<'a, 'db> CallArguments<'a, 'db> {
     /// Create a [`CallArguments`] from an iterator over non-variadic positional argument types.
-    pub(crate) fn positional(positional_tys: impl IntoIterator<Item = Type<'db>>) -> Self {
-        positional_tys
-            .into_iter()
-            .map(Argument::Positional)
-            .collect()
+    pub(crate) fn positional(
+        db: &'db dyn Db,
+        positional_tys: impl IntoIterator<Item = Type<'db>>,
+    ) -> Self {
+        CallArguments::new(
+            db,
+            positional_tys
+                .into_iter()
+                .map(Argument::Positional)
+                .collect::<Vec<_>>(),
+        )
     }
 
     /// Prepend an extra positional argument.
-    pub(crate) fn with_self(&self, self_ty: Type<'db>) -> Self {
-        let mut arguments = Vec::with_capacity(self.0.len() + 1);
+    pub(crate) fn with_self(&self, db: &'db dyn Db, self_ty: Type<'db>) -> Self {
+        let mut arguments = Vec::with_capacity(self.args(db).len() + 1);
         arguments.push(Argument::Synthetic(self_ty));
-        arguments.extend_from_slice(&self.0);
-        Self(arguments)
+        arguments.extend_from_slice(&self.args(db));
+        CallArguments::new(db, arguments)
     }
 
-    pub(crate) fn iter(&self) -> impl Iterator<Item = &Argument<'a, 'db>> {
-        self.0.iter()
+    pub(crate) fn args_iter(&self, db: &'db dyn Db) -> impl IntoIterator<Item = Argument<'db>> {
+        self.args(db).into_iter()
     }
 
     // TODO this should be eliminated in favor of [`bind_call`]
-    pub(crate) fn first_argument(&self) -> Option<Type<'db>> {
-        self.0.first().map(Argument::ty)
+    pub(crate) fn first_argument(&self, db: &'db dyn Db) -> Option<Type<'db>> {
+        self.args(db).first().map(Argument::ty)
+    }
+
+    // TODO this should be eliminated in favor of [`bind_call`]
+    pub(crate) fn second_argument(&self, db: &'db dyn Db) -> Option<Type<'db>> {
+        self.args(db).get(1).map(Argument::ty)
     }
 }
 
-impl<'db, 'a, 'b> IntoIterator for &'b CallArguments<'a, 'db> {
-    type Item = &'b Argument<'a, 'db>;
-    type IntoIter = std::slice::Iter<'b, Argument<'a, 'db>>;
-
-    fn into_iter(self) -> Self::IntoIter {
-        self.0.iter()
-    }
-}
-
-impl<'a, 'db> FromIterator<Argument<'a, 'db>> for CallArguments<'a, 'db> {
-    fn from_iter<T: IntoIterator<Item = Argument<'a, 'db>>>(iter: T) -> Self {
-        Self(iter.into_iter().collect())
-    }
-}
-
-#[derive(Clone, Debug)]
-pub(crate) enum Argument<'a, 'db> {
+#[derive(Clone, Debug, PartialEq, Eq, Hash, salsa::Update)]
+pub(crate) enum Argument<'db> {
     /// The synthetic `self` or `cls` argument, which doesn't appear explicitly at the call site.
     Synthetic(Type<'db>),
     /// A positional argument.
@@ -55,12 +62,12 @@ pub(crate) enum Argument<'a, 'db> {
     /// A starred positional argument (e.g. `*args`).
     Variadic(Type<'db>),
     /// A keyword argument (e.g. `a=1`).
-    Keyword { name: &'a str, ty: Type<'db> },
+    Keyword { name: Name, ty: Type<'db> },
     /// The double-starred keywords argument (e.g. `**kwargs`).
     Keywords(Type<'db>),
 }
 
-impl<'db> Argument<'_, 'db> {
+impl<'db> Argument<'db> {
     fn ty(&self) -> Type<'db> {
         match self {
             Self::Synthetic(ty) => *ty,

crates/red_knot_python_semantic/src/types/call/bind.rs

@@ -16,7 +16,7 @@ use ruff_text_size::Ranged;
 /// parameters, and any errors resulting from binding the call.
 pub(crate) fn bind_call<'db>(
     db: &'db dyn Db,
-    arguments: &CallArguments<'_, 'db>,
+    arguments: CallArguments<'db>,
     signature: &Signature<'db>,
     callable_ty: Type<'db>,
 ) -> CallBinding<'db> {
@@ -38,7 +38,7 @@ pub(crate) fn bind_call<'db>(
             None
         }
     };
-    for (argument_index, argument) in arguments.iter().enumerate() {
+    for (argument_index, argument) in arguments.args_iter(db).into_iter().enumerate() {
         let (index, parameter, argument_ty, positional) = match argument {
             Argument::Positional(ty) | Argument::Synthetic(ty) => {
                 if matches!(argument, Argument::Synthetic(_)) {
@@ -58,7 +58,7 @@ pub(crate) fn bind_call<'db>(
             }
             Argument::Keyword { name, ty } => {
                 let Some((index, parameter)) = parameters
-                    .keyword_by_name(name)
+                    .keyword_by_name(&name)
                     .or_else(|| parameters.keyword_variadic())
                 else {
                     errors.push(CallBindingError::UnknownArgument {
@@ -81,13 +81,13 @@ pub(crate) fn bind_call<'db>(
                     parameter: ParameterContext::new(parameter, index, positional),
                     argument_index: get_argument_index(argument_index, num_synthetic_args),
                     expected_ty,
-                    provided_ty: *argument_ty,
+                    provided_ty: argument_ty,
                 });
             }
         }
-        if let Some(existing) = parameter_tys[index].replace(*argument_ty) {
+        if let Some(existing) = parameter_tys[index].replace(argument_ty) {
             if parameter.is_variadic() || parameter.is_keyword_variadic() {
-                let union = UnionType::from_elements(db, [existing, *argument_ty]);
+                let union = UnionType::from_elements(db, [existing, argument_ty]);
                 parameter_tys[index].replace(union);
             } else {
                 errors.push(CallBindingError::ParameterAlreadyAssigned {
@@ -137,7 +137,7 @@ pub(crate) fn bind_call<'db>(
     }
 }
 
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq, salsa::Update)]
 pub(crate) struct CallBinding<'db> {
     /// Type of the callable object (function, class...)
     callable_ty: Type<'db>,
@@ -193,6 +193,13 @@ impl<'db> CallBinding<'db> {
         }
     }
 
+    pub(crate) fn three_parameter_types(&self) -> Option<(Type<'db>, Type<'db>, Type<'db>)> {
+        match self.parameter_types() {
+            [first, second, third] => Some((*first, *second, *third)),
+            _ => None,
+        }
+    }
+
     fn callable_name(&self, db: &'db dyn Db) -> Option<&str> {
         match self.callable_ty {
             Type::FunctionLiteral(function) => Some(function.name(db)),
@@ -266,7 +273,7 @@ impl std::fmt::Display for ParameterContexts {
     }
 }
 
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq, salsa::Update)]
 pub(crate) enum CallBindingError<'db> {
     /// The type of an argument is not assignable to the annotated type of its corresponding
     /// parameter.

crates/red_knot_python_semantic/src/types/class_base.rs

@@ -72,6 +72,7 @@ impl<'db> ClassBase<'db> {
             Type::Never
             | Type::BooleanLiteral(_)
             | Type::FunctionLiteral(_)
+            | Type::Callable(..)
             | Type::BytesLiteral(_)
             | Type::IntLiteral(_)
             | Type::StringLiteral(_)

crates/red_knot_python_semantic/src/types/display.rs

@@ -8,8 +8,8 @@ use ruff_python_literal::escape::AsciiEscape;
 
 use crate::types::class_base::ClassBase;
 use crate::types::{
-    ClassLiteralType, InstanceType, IntersectionType, KnownClass, StringLiteralType, Type,
-    UnionType,
+    CallableType, ClassLiteralType, InstanceType, IntersectionType, KnownClass, StringLiteralType,
+    Type, UnionType,
 };
 use crate::Db;
 use rustc_hash::FxHashMap;
@@ -88,6 +88,24 @@ impl Display for DisplayRepresentation<'_> {
             },
             Type::KnownInstance(known_instance) => f.write_str(known_instance.repr(self.db)),
             Type::FunctionLiteral(function) => f.write_str(function.name(self.db)),
+            Type::Callable(CallableType::BoundMethod(bound_method)) => {
+                write!(
+                    f,
+                    "<bound method `{method}` of `{instance}`>",
+                    method = bound_method.function(self.db).name(self.db),
+                    instance = bound_method.self_instance(self.db).display(self.db)
+                )
+            }
+            Type::Callable(CallableType::MethodWrapperDunderGet(function)) => {
+                write!(
+                    f,
+                    "<method-wrapper `__get__` of `{function}`>",
+                    function = function.name(self.db)
+                )
+            }
+            Type::Callable(CallableType::WrapperDescriptorDunderGet) => {
+                f.write_str("<wrapper-descriptor `__get__` of `function` objects>")
+            }
             Type::Union(union) => union.display(self.db).fmt(f),
             Type::Intersection(intersection) => intersection.display(self.db).fmt(f),
             Type::IntLiteral(n) => n.fmt(f),

crates/red_knot_python_semantic/src/types/infer.rs

@@ -1646,7 +1646,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                 }
 
                 let target_ty = enter_ty
-                    .try_call(self.db(), &CallArguments::positional([context_expression_ty]))
+                    .try_call(self.db(), CallArguments::positional(self.db(), [context_expression_ty]))
                     .map(|outcome| outcome.return_type(self.db()))
                     .unwrap_or_else(|err|  {
                         // TODO: Use more specific error messages for the different error cases.
@@ -1691,12 +1691,15 @@ impl<'db> TypeInferenceBuilder<'db> {
                         if exit_ty
                             .try_call(
                                 self.db(),
-                                &CallArguments::positional([
-                                    context_manager_ty,
-                                    Type::none(self.db()),
-                                    Type::none(self.db()),
-                                    Type::none(self.db()),
-                                ]),
+                                CallArguments::positional(
+                                    self.db(),
+                                    [
+                                        context_manager_ty,
+                                        Type::none(self.db()),
+                                        Type::none(self.db()),
+                                        Type::none(self.db()),
+                                    ],
+                                ),
                             )
                             .is_err()
                         {
@@ -2241,7 +2244,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                 {
                     let call = class_member.try_call(
                         self.db(),
-                        &CallArguments::positional([target_type, value_type]),
+                        CallArguments::positional(self.db(), [target_type, value_type]),
                     );
                     let augmented_return_ty = match call {
                         Ok(t) => t.return_type(self.db()),
@@ -2722,46 +2725,53 @@ impl<'db> TypeInferenceBuilder<'db> {
         &mut self,
         arguments: &'a ast::Arguments,
         parameter_expectations: ParameterExpectations,
-    ) -> CallArguments<'a, 'db> {
-        arguments
-            .arguments_source_order()
-            .enumerate()
-            .map(|(index, arg_or_keyword)| {
-                let infer_argument_type = match parameter_expectations.expectation_at_index(index) {
-                    ParameterExpectation::TypeExpression => Self::infer_type_expression,
-                    ParameterExpectation::ValueExpression => Self::infer_expression,
-                };
+    ) -> CallArguments<'db> {
+        CallArguments::new(
+            self.db(),
+            arguments
+                .arguments_source_order()
+                .enumerate()
+                .map(|(index, arg_or_keyword)| {
+                    let infer_argument_type =
+                        match parameter_expectations.expectation_at_index(index) {
+                            ParameterExpectation::TypeExpression => Self::infer_type_expression,
+                            ParameterExpectation::ValueExpression => Self::infer_expression,
+                        };
 
-                match arg_or_keyword {
-                    ast::ArgOrKeyword::Arg(arg) => match arg {
-                        ast::Expr::Starred(ast::ExprStarred {
+                    match arg_or_keyword {
+                        ast::ArgOrKeyword::Arg(arg) => match arg {
+                            ast::Expr::Starred(ast::ExprStarred {
+                                value,
+                                range: _,
+                                ctx: _,
+                            }) => {
+                                let ty = infer_argument_type(self, value);
+                                self.store_expression_type(arg, ty);
+                                Argument::Variadic(ty)
+                            }
+                            // TODO diagnostic if after a keyword argument
+                            _ => Argument::Positional(infer_argument_type(self, arg)),
+                        },
+                        ast::ArgOrKeyword::Keyword(ast::Keyword {
+                            arg,
                             value,
                             range: _,
-                            ctx: _,
                         }) => {
                             let ty = infer_argument_type(self, value);
-                            self.store_expression_type(arg, ty);
-                            Argument::Variadic(ty)
-                        }
-                        // TODO diagnostic if after a keyword argument
-                        _ => Argument::Positional(infer_argument_type(self, arg)),
-                    },
-                    ast::ArgOrKeyword::Keyword(ast::Keyword {
-                        arg,
-                        value,
-                        range: _,
-                    }) => {
-                        let ty = infer_argument_type(self, value);
-                        if let Some(arg) = arg {
-                            Argument::Keyword { name: &arg.id, ty }
-                        } else {
-                            // TODO diagnostic if not last
-                            Argument::Keywords(ty)
+                            if let Some(arg) = arg {
+                                Argument::Keyword {
+                                    name: arg.id.clone(),
+                                    ty,
+                                }
+                            } else {
+                                // TODO diagnostic if not last
+                                Argument::Keywords(ty)
+                            }
                         }
                     }
-                }
-            })
-            .collect()
+                })
+                .collect::<Vec<_>>(),
+        )
     }
 
     fn infer_optional_expression(&mut self, expression: Option<&ast::Expr>) -> Option<Type<'db>> {
@@ -3277,7 +3287,7 @@ impl<'db> TypeInferenceBuilder<'db> {
             .unwrap_or_default();
 
         let call_arguments = self.infer_arguments(arguments, parameter_expectations);
-        let call = function_type.try_call(self.db(), &call_arguments);
+        let call = function_type.try_call(self.db(), call_arguments);
 
         match call {
             Ok(outcome) => {
@@ -3753,6 +3763,7 @@ impl<'db> TypeInferenceBuilder<'db> {
             (
                 op @ (ast::UnaryOp::UAdd | ast::UnaryOp::USub | ast::UnaryOp::Invert),
                 Type::FunctionLiteral(_)
+                | Type::Callable(..)
                 | Type::ModuleLiteral(_)
                 | Type::ClassLiteral(_)
                 | Type::SubclassOf(_)
@@ -3780,7 +3791,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                 match operand_type.try_call_dunder(
                     self.db(),
                     unary_dunder_method,
-                    &CallArguments::positional([operand_type]),
+                    CallArguments::none(self.db()),
                 ) {
                     Ok(outcome) => outcome.return_type(self.db()),
                     Err(e) => {
@@ -3967,6 +3978,7 @@ impl<'db> TypeInferenceBuilder<'db> {
             // fall back on looking for dunder methods on one of the operand types.
             (
                 Type::FunctionLiteral(_)
+                | Type::Callable(..)
                 | Type::ModuleLiteral(_)
                 | Type::ClassLiteral(_)
                 | Type::SubclassOf(_)
@@ -3983,6 +3995,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                 | Type::SliceLiteral(_)
                 | Type::Tuple(_),
                 Type::FunctionLiteral(_)
+                | Type::Callable(..)
                 | Type::ModuleLiteral(_)
                 | Type::ClassLiteral(_)
                 | Type::SubclassOf(_)
@@ -4029,7 +4042,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                             .try_call_dunder(
                                 self.db(),
                                 reflected_dunder,
-                                &CallArguments::positional([right_ty, left_ty]),
+                                CallArguments::positional(self.db(), [left_ty]),
                             )
                             .map(|outcome| outcome.return_type(self.db()))
                             .or_else(|_| {
@@ -4037,7 +4050,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                                     .try_call_dunder(
                                         self.db(),
                                         op.dunder(),
-                                        &CallArguments::positional([left_ty, right_ty]),
+                                        CallArguments::positional(self.db(), [right_ty]),
                                     )
                                     .map(|outcome| outcome.return_type(self.db()))
                             })
@@ -4050,7 +4063,10 @@ impl<'db> TypeInferenceBuilder<'db> {
                     left_class.member(self.db(), op.dunder())
                 {
                     class_member
-                        .try_call(self.db(), &CallArguments::positional([left_ty, right_ty]))
+                        .try_call(
+                            self.db(),
+                            CallArguments::positional(self.db(), [left_ty, right_ty]),
+                        )
                         .map(|outcome| outcome.return_type(self.db()))
                         .ok()
                 } else {
@@ -4068,7 +4084,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                             class_member
                                 .try_call(
                                     self.db(),
-                                    &CallArguments::positional([right_ty, left_ty]),
+                                    CallArguments::positional(self.db(), [right_ty, left_ty]),
                                 )
                                 .map(|outcome| outcome.return_type(self.db()))
                                 .ok()
@@ -4637,21 +4653,23 @@ impl<'db> TypeInferenceBuilder<'db> {
         let db = self.db();
         // The following resource has details about the rich comparison algorithm:
         // https://snarky.ca/unravelling-rich-comparison-operators/
-        let call_dunder = |op: RichCompareOperator,
-                           left: InstanceType<'db>,
-                           right: InstanceType<'db>| {
-            // TODO: How do we want to handle possibly unbound dunder methods?
-            match left.class.class_member(db, op.dunder()) {
-                Symbol::Type(class_member_dunder, Boundness::Bound) => class_member_dunder
-                    .try_call(
-                        db,
-                        &CallArguments::positional([Type::Instance(left), Type::Instance(right)]),
-                    )
-                    .map(|outcome| outcome.return_type(db))
-                    .ok(),
-                _ => None,
-            }
-        };
+        let call_dunder =
+            |op: RichCompareOperator, left: InstanceType<'db>, right: InstanceType<'db>| {
+                // TODO: How do we want to handle possibly unbound dunder methods?
+                match left.class.class_member(db, op.dunder()) {
+                    Symbol::Type(class_member_dunder, Boundness::Bound) => class_member_dunder
+                        .try_call(
+                            db,
+                            CallArguments::positional(
+                                db,
+                                [Type::Instance(left), Type::Instance(right)],
+                            ),
+                        )
+                        .map(|outcome| outcome.return_type(db))
+                        .ok(),
+                    _ => None,
+                }
+            };
 
         // The reflected dunder has priority if the right-hand side is a strict subclass of the left-hand side.
         if left != right && right.is_subtype_of(db, left) {
@@ -4695,7 +4713,10 @@ impl<'db> TypeInferenceBuilder<'db> {
                 contains_dunder
                     .try_call(
                         db,
-                        &CallArguments::positional([Type::Instance(right), Type::Instance(left)]),
+                        CallArguments::positional(
+                            db,
+                            [Type::Instance(right), Type::Instance(left)],
+                        ),
                     )
                     .map(|outcome| outcome.return_type(db))
                     .ok()
@@ -4953,7 +4974,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                 match value_ty.try_call_dunder(
                     self.db(),
                     "__getitem__",
-                    &CallArguments::positional([value_ty, slice_ty]),
+                    CallArguments::positional(self.db(), [slice_ty]),
                 ) {
                     Ok(outcome) => return outcome.return_type(self.db()),
                     Err(err @ CallDunderError::PossiblyUnbound { .. }) => {
@@ -5014,7 +5035,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                             }
 
                             return ty
-                                .try_call(self.db(), &CallArguments::positional([value_ty, slice_ty]))
+                                .try_call(self.db(), CallArguments::positional(self.db(),[value_ty, slice_ty]))
                                 .map(|outcome| outcome.return_type(self.db()))
                                 .unwrap_or_else(|err| {
                                     self.context.report_lint(

crates/red_knot_python_semantic/src/types/property_tests.rs

@@ -29,9 +29,10 @@ use std::sync::{Arc, Mutex, MutexGuard, OnceLock};
 use crate::db::tests::{setup_db, TestDb};
 use crate::symbol::{builtins_symbol, known_module_symbol};
 use crate::types::{
-    IntersectionBuilder, KnownClass, KnownInstanceType, SubclassOfType, TupleType, Type, UnionType,
+    BoundMethodType, CallableType, IntersectionBuilder, KnownClass, KnownInstanceType,
+    SubclassOfType, TupleType, Type, UnionType,
 };
-use crate::KnownModule;
+use crate::{Db, KnownModule};
 use quickcheck::{Arbitrary, Gen};
 
 /// A test representation of a type that can be transformed unambiguously into a real Type,
@@ -67,6 +68,24 @@ pub(crate) enum Ty {
     SubclassOfAbcClass(&'static str),
     AlwaysTruthy,
     AlwaysFalsy,
+    BuiltinsFunction(&'static str),
+    BuiltinsBoundMethod {
+        class: &'static str,
+        method: &'static str,
+    },
+}
+
+#[salsa::tracked]
+fn create_bound_method<'db>(
+    db: &'db dyn Db,
+    function: Type<'db>,
+    builtins_class: Type<'db>,
+) -> Type<'db> {
+    Type::Callable(CallableType::BoundMethod(BoundMethodType::new(
+        db,
+        function.expect_function_literal(),
+        builtins_class.to_instance(db),
+    )))
 }
 
 impl Ty {
@@ -123,6 +142,13 @@ impl Ty {
             ),
             Ty::AlwaysTruthy => Type::AlwaysTruthy,
             Ty::AlwaysFalsy => Type::AlwaysFalsy,
+            Ty::BuiltinsFunction(name) => builtins_symbol(db, name).expect_type(),
+            Ty::BuiltinsBoundMethod { class, method } => {
+                let builtins_class = builtins_symbol(db, class).expect_type();
+                let function = builtins_class.static_member(db, method).expect_type();
+
+                create_bound_method(db, function, builtins_class)
+            }
         }
     }
 }
@@ -173,6 +199,16 @@ fn arbitrary_core_type(g: &mut Gen) -> Ty {
         Ty::SubclassOfAbcClass("ABCMeta"),
         Ty::AlwaysTruthy,
         Ty::AlwaysFalsy,
+        Ty::BuiltinsFunction("chr"),
+        Ty::BuiltinsFunction("ascii"),
+        Ty::BuiltinsBoundMethod {
+            class: "str",
+            method: "isascii",
+        },
+        Ty::BuiltinsBoundMethod {
+            class: "int",
+            method: "bit_length",
+        },
     ])
     .unwrap()
     .clone()

crates/red_knot_python_semantic/src/types/signatures.rs

@@ -21,6 +21,13 @@ pub(crate) struct Signature<'db> {
 }
 
 impl<'db> Signature<'db> {
+    pub(crate) fn new(parameters: Parameters<'db>, return_ty: Option<Type<'db>>) -> Self {
+        Self {
+            parameters,
+            return_ty,
+        }
+    }
+
     /// Return a todo signature: (*args: Todo, **kwargs: Todo) -> Todo
     pub(crate) fn todo() -> Self {
         Self {
@@ -64,6 +71,10 @@ impl<'db> Signature<'db> {
 pub(crate) struct Parameters<'db>(Vec<Parameter<'db>>);
 
 impl<'db> Parameters<'db> {
+    pub(crate) fn new(parameters: impl IntoIterator<Item = Parameter<'db>>) -> Self {
+        Self(parameters.into_iter().collect())
+    }
+
     /// Return todo parameters: (*args: Todo, **kwargs: Todo)
     fn todo() -> Self {
         Self(vec![
@@ -233,6 +244,18 @@ pub(crate) struct Parameter<'db> {
 }
 
 impl<'db> Parameter<'db> {
+    pub(crate) fn new(
+        name: Option<Name>,
+        annotated_ty: Option<Type<'db>>,
+        kind: ParameterKind<'db>,
+    ) -> Self {
+        Self {
+            name,
+            annotated_ty,
+            kind,
+        }
+    }
+
     fn from_node_and_kind(
         db: &'db dyn Db,
         definition: Definition<'db>,

crates/red_knot_python_semantic/src/types/subclass_of.rs

@@ -64,8 +64,8 @@ impl<'db> SubclassOfType<'db> {
         !self.is_dynamic()
     }
 
-    pub(crate) fn member(self, db: &'db dyn Db, name: &str) -> Symbol<'db> {
-        Type::from(self.subclass_of).member(db, name)
+    pub(crate) fn static_member(self, db: &'db dyn Db, name: &str) -> Symbol<'db> {
+        Type::from(self.subclass_of).static_member(db, name)
     }
 
     /// Return `true` if `self` is a subtype of `other`.

crates/red_knot_python_semantic/src/types/type_ordering.rs

@@ -1,5 +1,7 @@
 use std::cmp::Ordering;
 
+use crate::types::CallableType;
+
 use super::{
     class_base::ClassBase, ClassLiteralType, DynamicType, InstanceType, KnownInstanceType,
     TodoType, Type,
@@ -54,6 +56,27 @@ pub(super) fn union_elements_ordering<'db>(left: &Type<'db>, right: &Type<'db>)
         (Type::FunctionLiteral(_), _) => Ordering::Less,
         (_, Type::FunctionLiteral(_)) => Ordering::Greater,
 
+        (
+            Type::Callable(CallableType::BoundMethod(left)),
+            Type::Callable(CallableType::BoundMethod(right)),
+        ) => left.cmp(right),
+        (Type::Callable(CallableType::BoundMethod(_)), _) => Ordering::Less,
+        (_, Type::Callable(CallableType::BoundMethod(_))) => Ordering::Greater,
+
+        (
+            Type::Callable(CallableType::MethodWrapperDunderGet(left)),
+            Type::Callable(CallableType::MethodWrapperDunderGet(right)),
+        ) => left.cmp(right),
+        (Type::Callable(CallableType::MethodWrapperDunderGet(_)), _) => Ordering::Less,
+        (_, Type::Callable(CallableType::MethodWrapperDunderGet(_))) => Ordering::Greater,
+
+        (
+            Type::Callable(CallableType::WrapperDescriptorDunderGet),
+            Type::Callable(CallableType::WrapperDescriptorDunderGet),
+        ) => Ordering::Equal,
+        (Type::Callable(CallableType::WrapperDescriptorDunderGet), _) => Ordering::Less,
+        (_, Type::Callable(CallableType::WrapperDescriptorDunderGet)) => Ordering::Greater,
+
         (Type::Tuple(left), Type::Tuple(right)) => left.cmp(right),
         (Type::Tuple(_), _) => Ordering::Less,
         (_, Type::Tuple(_)) => Ordering::Greater,