[red-knot] Infer the members of a protocol class

Author: AlexWaygood

crates/red_knot_python_semantic/resources/mdtest/protocols.md

@@ -368,16 +368,8 @@ class Foo(Protocol):
     def method_member(self) -> bytes:
         return b"foo"
 
-# TODO: at runtime, `get_protocol_members` returns a `frozenset`,
-# but for now we might pretend it returns a `tuple`, as we support heterogeneous `tuple` types
-# but not yet generic `frozenset`s
-#
-# So this should either be
-#
-# `tuple[Literal["x"], Literal["y"], Literal["z"], Literal["method_member"]]`
-#
-# `frozenset[Literal["x", "y", "z", "method_member"]]`
-reveal_type(get_protocol_members(Foo))  # revealed: @Todo(specialized non-generic class)
+# 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"]]
 ```
 
 Certain special attributes and methods are not considered protocol members at runtime, and should
@@ -395,8 +387,8 @@ class Lumberjack(Protocol):
     def __init__(self, x: int) -> None:
         self.x = x
 
-# TODO: `tuple[Literal["x"]]` or `frozenset[Literal["x"]]`
-reveal_type(get_protocol_members(Lumberjack))  # revealed: @Todo(specialized non-generic class)
+# TODO: actually a frozenset
+reveal_type(get_protocol_members(Lumberjack))  # revealed: tuple[Literal["x"]]
 ```
 
 A sub-protocol inherits and extends the members of its superclass protocol(s):
@@ -408,15 +400,14 @@ class Bar(Protocol):
 class Baz(Bar, Protocol):
     ham: memoryview
 
-# TODO: `tuple[Literal["spam", "ham"]]` or `frozenset[Literal["spam", "ham"]]`
-reveal_type(get_protocol_members(Baz))  # revealed: @Todo(specialized non-generic class)
+# TODO: actually a frozenset
+reveal_type(get_protocol_members(Baz))  # revealed: tuple[Literal["ham"], Literal["spam"]]
 
 class Baz2(Bar, Foo, Protocol): ...
 
-# TODO: either
-# `tuple[Literal["spam"], Literal["x"], Literal["y"], Literal["z"], Literal["method_member"]]`
-# or `frozenset[Literal["spam", "x", "y", "z", "method_member"]]`
-reveal_type(get_protocol_members(Baz2))  # revealed: @Todo(specialized non-generic class)
+# TODO: actually a frozenset
+# revealed: tuple[Literal["method_member"], Literal["spam"], Literal["x"], Literal["y"], Literal["z"]]
+reveal_type(get_protocol_members(Baz2))
 ```
 
 ## Invalid calls to `get_protocol_members()`
@@ -640,9 +631,9 @@ class LotsOfBindings(Protocol):
         case l:  # TODO: this should error with `[invalid-protocol]` (`l` is not declared)
             ...
 
-# TODO: all bindings in the above class should be understood as protocol members,
-# even those that we complained about with a diagnostic
-reveal_type(get_protocol_members(LotsOfBindings))  # revealed: @Todo(specialized non-generic class)
+# 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"]]
+reveal_type(get_protocol_members(LotsOfBindings))
 ```
 
 Attribute members are allowed to have assignments in methods on the protocol class, just like

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

@@ -21,7 +21,7 @@ use crate::types::signatures::{Parameter, ParameterForm};
 use crate::types::{
     BoundMethodType, DataclassParams, DataclassTransformerParams, FunctionDecorators, FunctionType,
     KnownClass, KnownFunction, KnownInstanceType, MethodWrapperKind, PropertyInstanceType,
-    UnionType, WrapperDescriptorKind,
+    TupleType, UnionType, WrapperDescriptorKind,
 };
 use ruff_db::diagnostic::{Annotation, Severity, Span, SubDiagnostic};
 use ruff_python_ast as ast;
@@ -568,6 +568,21 @@ 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) {
+                                overload.set_return_type(Type::Tuple(TupleType::new(
+                                    db,
+                                    protocol_class
+                                        .members(db)
+                                        .iter()
+                                        .map(|member| Type::string_literal(db, member))
+                                        .collect::<Box<[Type<'db>]>>(),
+                                )));
+                            }
+                        }
+                    }
+
                     Some(KnownFunction::Overload) => {
                         // TODO: This can be removed once we understand legacy generics because the
                         // typeshed definition for `typing.overload` is an identity function.

crates/red_knot_python_semantic/src/types/class.rs

@@ -1,4 +1,5 @@
 use std::hash::BuildHasherDefault;
+use std::ops::Deref;
 use std::sync::{LazyLock, Mutex};
 
 use super::{
@@ -13,6 +14,7 @@ use crate::types::signatures::{Parameter, Parameters};
 use crate::types::{
     CallableType, DataclassParams, DataclassTransformerParams, KnownInstanceType, Signature,
 };
+use crate::FxOrderSet;
 use crate::{
     module_resolver::file_to_module,
     semantic_index::{
@@ -1665,6 +1667,11 @@ impl<'db> ClassLiteralType<'db> {
             Some(InheritanceCycle::Inherited)
         }
     }
+
+    /// Returns `Some` if this is a protocol class, `None` otherwise.
+    pub(super) fn into_protocol_class(self, db: &'db dyn Db) -> Option<ProtocolClassLiteral<'db>> {
+        self.is_protocol(db).then_some(ProtocolClassLiteral(self))
+    }
 }
 
 impl<'db> From<ClassLiteralType<'db>> for Type<'db> {
@@ -1676,6 +1683,86 @@ impl<'db> From<ClassLiteralType<'db>> for Type<'db> {
     }
 }
 
+/// Representation of a single `Protocol` class definition.
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+pub(super) struct ProtocolClassLiteral<'db>(ClassLiteralType<'db>);
+
+impl<'db> ProtocolClassLiteral<'db> {
+    pub(super) fn members(self, db: &'db dyn Db) -> &'db ordermap::set::Slice<Name> {
+        /// The list of excluded members is subject to change between Python versions,
+        /// especially for dunders, but it probably doesn't matter *too* much if this
+        /// list goes out of date. It's up-to-date as of Python commit 87b1ea016b1454b1e83b9113fa9435849b7743aa
+        /// (<https://github.com/python/cpython/blob/87b1ea016b1454b1e83b9113fa9435849b7743aa/Lib/typing.py#L1776-L1791>)
+        fn excluded_from_proto_members(member: &str) -> bool {
+            matches!(
+                member,
+                "_is_protocol"
+                    | "__non_callable_proto_members__"
+                    | "__static_attributes__"
+                    | "__orig_class__"
+                    | "__match_args__"
+                    | "__weakref__"
+                    | "__doc__"
+                    | "__parameters__"
+                    | "__module__"
+                    | "_MutableMapping__marker"
+                    | "__slots__"
+                    | "__dict__"
+                    | "__new__"
+                    | "__protocol_attrs__"
+                    | "__init__"
+                    | "__class_getitem__"
+                    | "__firstlineno__"
+                    | "__abstractmethods__"
+                    | "__orig_bases__"
+                    | "_is_runtime_protocol"
+                    | "__subclasshook__"
+                    | "__type_params__"
+                    | "__annotations__"
+                    | "__annotate__"
+                    | "__annotate_func__"
+                    | "__annotations_cache__"
+            )
+        }
+
+        #[salsa::tracked(return_ref)]
+        fn cached_members<'db>(
+            db: &'db dyn Db,
+            class: ClassLiteralType<'db>,
+        ) -> Box<ordermap::set::Slice<Name>> {
+            let mut members = FxOrderSet::default();
+
+            for parent_protocol in class
+                .iter_mro(db, None)
+                .filter_map(ClassBase::into_class)
+                .filter_map(|class| class.class_literal(db).0.into_protocol_class(db))
+            {
+                members.extend(
+                    symbol_table(db, parent_protocol.body_scope(db))
+                        .symbols()
+                        .filter(|symbol| symbol.is_bound() || symbol.is_declared())
+                        .map(crate::semantic_index::symbol::Symbol::name)
+                        .filter(|name| !excluded_from_proto_members(name))
+                        .cloned(),
+                );
+            }
+
+            members.sort();
+            members.into_boxed_slice()
+        }
+
+        cached_members(db, *self)
+    }
+}
+
+impl<'db> Deref for ProtocolClassLiteral<'db> {
+    type Target = ClassLiteralType<'db>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub(super) enum InheritanceCycle {
     /// The class is cyclically defined and is a participant in the cycle.