[ty] get_protocol_members returns a frozenset, not a tuple (#18284)

Author: AlexWaygood

crates/ty_python_semantic/resources/mdtest/protocols.md

@@ -375,8 +375,7 @@ class Foo(Protocol):
     def method_member(self) -> bytes:
         return b"foo"
 
-# TODO: actually a frozenset (requires support for legacy generics)
-reveal_type(get_protocol_members(Foo))  # revealed: tuple[Literal["method_member"], Literal["x"], Literal["y"], Literal["z"]]
+reveal_type(get_protocol_members(Foo))  # revealed: frozenset[Literal["method_member", "x", "y", "z"]]
 ```
 
 Certain special attributes and methods are not considered protocol members at runtime, and should
@@ -394,8 +393,7 @@ class Lumberjack(Protocol):
     def __init__(self, x: int) -> None:
         self.x = x
 
-# TODO: actually a frozenset
-reveal_type(get_protocol_members(Lumberjack))  # revealed: tuple[Literal["x"]]
+reveal_type(get_protocol_members(Lumberjack))  # revealed: frozenset[Literal["x"]]
 ```
 
 A sub-protocol inherits and extends the members of its superclass protocol(s):
@@ -407,13 +405,11 @@ class Bar(Protocol):
 class Baz(Bar, Protocol):
     ham: memoryview
 
-# TODO: actually a frozenset
-reveal_type(get_protocol_members(Baz))  # revealed: tuple[Literal["ham"], Literal["spam"]]
+reveal_type(get_protocol_members(Baz))  # revealed: frozenset[Literal["ham", "spam"]]
 
 class Baz2(Bar, Foo, Protocol): ...
 
-# TODO: actually a frozenset
-# revealed: tuple[Literal["method_member"], Literal["spam"], Literal["x"], Literal["y"], Literal["z"]]
+# revealed: frozenset[Literal["method_member", "spam", "x", "y", "z"]]
 reveal_type(get_protocol_members(Baz2))
 ```
 
@@ -441,8 +437,7 @@ class Foo(Protocol):
         e = 56
         def f(self) -> None: ...
 
-# TODO: actually a frozenset
-reveal_type(get_protocol_members(Foo))  # revealed: tuple[Literal["d"], Literal["e"], Literal["f"]]
+reveal_type(get_protocol_members(Foo))  # revealed: frozenset[Literal["d", "e", "f"]]
 ```
 
 ## Invalid calls to `get_protocol_members()`
@@ -673,8 +668,7 @@ class LotsOfBindings(Protocol):
         case l:  # TODO: this should error with `[invalid-protocol]` (`l` is not declared)
             ...
 
-# TODO: actually a frozenset
-# revealed: tuple[Literal["Nested"], Literal["NestedProtocol"], Literal["a"], Literal["b"], Literal["c"], Literal["d"], Literal["e"], Literal["f"], Literal["g"], Literal["h"], Literal["i"], Literal["j"], Literal["k"], Literal["l"]]
+# revealed: frozenset[Literal["Nested", "NestedProtocol", "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l"]]
 reveal_type(get_protocol_members(LotsOfBindings))
 ```
 
@@ -702,9 +696,7 @@ class Foo(Protocol):
 
 # Note: the list of members does not include `a`, `b` or `c`,
 # as none of these attributes is declared in the class body.
-#
-# TODO: actually a frozenset
-reveal_type(get_protocol_members(Foo))  # revealed: tuple[Literal["non_init_method"], Literal["x"], Literal["y"]]
+reveal_type(get_protocol_members(Foo))  # revealed: frozenset[Literal["non_init_method", "x", "y"]]
 ```
 
 If a member is declared in a superclass of a protocol class, it is fine for it to be assigned to in
@@ -717,9 +709,8 @@ class Super(Protocol):
 class Sub(Super, Protocol):
     x = 42  # no error here, since it's declared in the superclass
 
-# TODO: actually frozensets
-reveal_type(get_protocol_members(Super))  # revealed: tuple[Literal["x"]]
-reveal_type(get_protocol_members(Sub))  # revealed: tuple[Literal["x"]]
+reveal_type(get_protocol_members(Super))  # revealed: frozenset[Literal["x"]]
+reveal_type(get_protocol_members(Sub))  # revealed: frozenset[Literal["x"]]
 ```
 
 If a protocol has 0 members, then all other types are assignable to it, and all fully static types

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

@@ -667,15 +667,15 @@ impl<'db> Bindings<'db> {
                         Some(KnownFunction::GetProtocolMembers) => {
                             if let [Some(Type::ClassLiteral(class))] = overload.parameter_types() {
                                 if let Some(protocol_class) = class.into_protocol_class(db) {
-                                    // TODO: actually a frozenset at runtime (requires support for legacy generic classes)
-                                    overload.set_return_type(Type::Tuple(TupleType::new(
-                                        db,
-                                        protocol_class
-                                            .interface(db)
-                                            .members(db)
-                                            .map(|member| Type::string_literal(db, member.name()))
-                                            .collect::<Box<[Type<'db>]>>(),
-                                    )));
+                                    let member_names = protocol_class
+                                        .interface(db)
+                                        .members(db)
+                                        .map(|member| Type::string_literal(db, member.name()));
+                                    let specialization = UnionType::from_elements(db, member_names);
+                                    overload.set_return_type(
+                                        KnownClass::FrozenSet
+                                            .to_specialized_instance(db, [specialization]),
+                                    );
                                 }
                             }
                         }