[red-knot] Three-argument type-calls take 'str' as the first argument

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

@@ -26,7 +26,11 @@ reveal_type(type(1))  # revealed: Literal[int]
 But a three-argument call to type creates a dynamic instance of the `type` class:
 
 ```py
+class Base: ...
+
 reveal_type(type("Foo", (), {}))  # revealed: type
+
+reveal_type(type("Foo", (Base,), {"attr": 1}))  # revealed: type
 ```
 
 Other numbers of arguments are invalid
@@ -39,6 +43,24 @@ type("Foo", ())
 type("Foo", (), {}, weird_other_arg=42)
 ```
 
+The following calls are also invalid, due to incorrect argument types:
+
+```py
+class Base: ...
+
+# error: [no-matching-overload] "No overload of class `type` matches arguments"
+type(b"Foo", (), {})
+
+# error: [no-matching-overload] "No overload of class `type` matches arguments"
+type("Foo", Base, {})
+
+# TODO: this should be an error
+type("Foo", (1, 2), {})
+
+# TODO: this should be an error
+type("Foo", (Base,), {b"attr": 1})
+```
+
 ## Calls to `str()`
 
 ### Valid calls

crates/red_knot_python_semantic/resources/mdtest/narrow/type.md

@@ -76,6 +76,9 @@ No narrowing should occur if `type` is used to dynamically create a class:
 
 ```py
 def _(x: str | int):
+    # The following diagnostic is valid, since the three-argument form of `type`
+    # can only be called with `str` as the first argument.
+    # error: [no-matching-overload] "No overload of class `type` matches arguments"
     if type(x, (), {}) is str:
         reveal_type(x)  # revealed: str | int
     else:

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

@@ -194,6 +194,9 @@ static_assert(is_assignable_to(tuple[int, str], tuple[int, str]))
 static_assert(is_assignable_to(tuple[Literal[1], Literal[2]], tuple[int, int]))
 static_assert(is_assignable_to(tuple[Any, Literal[2]], tuple[int, int]))
 static_assert(is_assignable_to(tuple[Literal[1], Any], tuple[int, int]))
+static_assert(is_assignable_to(tuple[()], tuple))
+static_assert(is_assignable_to(tuple[int, str], tuple))
+static_assert(is_assignable_to(tuple[Any], tuple))
 
 static_assert(not is_assignable_to(tuple[()], tuple[int]))
 static_assert(not is_assignable_to(tuple[int], tuple[str]))

crates/red_knot_python_semantic/src/types.rs

@@ -950,6 +950,15 @@ impl<'db> Type<'db> {
                     )
             }
 
+            // Any heterogeneous tuple type is assignable to `tuple`. This needs to be a special
+            // case because the left-hand side tuple might be a gradual type, so we can not rely
+            // on subtyping.
+            (Type::Tuple(_), Type::Instance(instance))
+                if instance.class.is_known(db, KnownClass::Tuple) =>
+            {
+                true
+            }
+
             // `type[Any]` is assignable to any `type[...]` type, because `type[Any]` can
             // materialize to any `type[...]` type.
             (Type::SubclassOf(subclass_of_ty), Type::SubclassOf(_))
@@ -2903,12 +2912,14 @@ impl<'db> Type<'db> {
                             ),
                             Signature::new(
                                 Parameters::new([
-                                    Parameter::positional_only(Some(Name::new_static("o")))
-                                        .with_annotated_type(Type::any()),
+                                    Parameter::positional_only(Some(Name::new_static("name")))
+                                        .with_annotated_type(KnownClass::Str.to_instance(db)),
                                     Parameter::positional_only(Some(Name::new_static("bases")))
-                                        .with_annotated_type(Type::any()),
+                                        // TODO: Should be tuple[type, ...] once we have support for homogenous tuples
+                                        .with_annotated_type(KnownClass::Tuple.to_instance(db)),
                                     Parameter::positional_only(Some(Name::new_static("dict")))
-                                        .with_annotated_type(Type::any()),
+                                        // TODO: Should be `dict[str, Any]` once we have support for generics
+                                        .with_annotated_type(KnownClass::Dict.to_instance(db)),
                                 ]),
                                 Some(KnownClass::Type.to_instance(db)),
                             ),