[red-knot] Infer the members of a protocol class (#17556)

crates/red_knot_python_semantic/resources/mdtest/protocols.md

@@ -315,7 +315,7 @@ reveal_type(Protocol())  # revealed: Unknown
 class MyProtocol(Protocol):
     x: int
 
-# error
+# TODO: should emit error
 reveal_type(MyProtocol())  # revealed: MyProtocol
 ```
 
@@ -363,16 +363,8 @@ class Foo(Protocol):
     def method_member(self) -> bytes:
         return b"foo"
 
-# TODO: at runtime, `get_protocol_members` returns a `frozenset`,
+# TODO: actually a frozenset (requires support for legacy generics)
-# but for now we might pretend it returns a `tuple`, as we support heterogeneous `tuple` types
+reveal_type(get_protocol_members(Foo))  # revealed: tuple[Literal["method_member"], Literal["x"], Literal["y"], Literal["z"]]
-# 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)
 ```
 
 Certain special attributes and methods are not considered protocol members at runtime, and should
@@ -390,8 +382,8 @@ class Lumberjack(Protocol):
     def __init__(self, x: int) -> None:
         self.x = x
 
-# TODO: `tuple[Literal["x"]]` or `frozenset[Literal["x"]]`
+# TODO: actually a frozenset
-reveal_type(get_protocol_members(Lumberjack))  # revealed: @Todo(specialized non-generic class)
+reveal_type(get_protocol_members(Lumberjack))  # revealed: tuple[Literal["x"]]
 ```
 
 A sub-protocol inherits and extends the members of its superclass protocol(s):
@@ -403,15 +395,42 @@ class Bar(Protocol):
 class Baz(Bar, Protocol):
     ham: memoryview
 
-# TODO: `tuple[Literal["spam", "ham"]]` or `frozenset[Literal["spam", "ham"]]`
+# TODO: actually a frozenset
-reveal_type(get_protocol_members(Baz))  # revealed: @Todo(specialized non-generic class)
+reveal_type(get_protocol_members(Baz))  # revealed: tuple[Literal["ham"], Literal["spam"]]
 
 class Baz2(Bar, Foo, Protocol): ...
 
-# TODO: either
+# TODO: actually a frozenset
-# `tuple[Literal["spam"], Literal["x"], Literal["y"], Literal["z"], Literal["method_member"]]`
+# revealed: tuple[Literal["method_member"], Literal["spam"], Literal["x"], Literal["y"], Literal["z"]]
-# or `frozenset[Literal["spam", "x", "y", "z", "method_member"]]`
+reveal_type(get_protocol_members(Baz2))
-reveal_type(get_protocol_members(Baz2))  # revealed: @Todo(specialized non-generic class)
+```
+
+## Protocol members in statically known branches
+
+The list of protocol members does not include any members declared in branches that are statically
+known to be unreachable:
+
+```toml
+[environment]
+python-version = "3.9"
+```
+
+```py
+import sys
+from typing_extensions import Protocol, get_protocol_members
+
+class Foo(Protocol):
+    if sys.version_info >= (3, 10):
+        a: int
+        b = 42
+        def c(self) -> None: ...
+    else:
+        d: int
+        e = 56
+        def f(self) -> None: ...
+
+# TODO: actually a frozenset
+reveal_type(get_protocol_members(Foo))  # revealed: tuple[Literal["d"], Literal["e"], Literal["f"]]
 ```
 
 ## Invalid calls to `get_protocol_members()`
@@ -639,14 +658,14 @@ 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,
+# TODO: actually a frozenset
-# even those that we complained about with a diagnostic
+# 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))  # revealed: @Todo(specialized non-generic class)
+reveal_type(get_protocol_members(LotsOfBindings))
 ```
 
 Attribute members are allowed to have assignments in methods on the protocol class, just like
-non-protocol classes. Unlike other classes, however, *implicit* instance attributes -- those that
+non-protocol classes. Unlike other classes, however, instance attributes that are not declared in
-are not declared in the class body -- are not allowed:
+the class body are disallowed:
 
 ```py
 class Foo(Protocol):
@@ -655,11 +674,18 @@ class Foo(Protocol):
 
     def __init__(self) -> None:
         self.x = 42  # fine
-        self.a = 56  # error
+        self.a = 56  # TODO: should emit diagnostic
+        self.b: int = 128  # TODO: should emit diagnostic
 
     def non_init_method(self) -> None:
         self.y = 64  # fine
-        self.b = 72  # error
+        self.c = 72  # TODO: should emit diagnostic
+
+# 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"]]
 ```
 
 If a protocol has 0 members, then all other types are assignable to it, and all fully static types

crates/red_knot_python_semantic/src/semantic_index/use_def.rs

@@ -437,6 +437,15 @@ impl<'db> UseDefMap<'db> {
             .map(|symbol_id| (symbol_id, self.public_declarations(symbol_id)))
     }
 
+    pub(crate) fn all_public_bindings<'map>(
+        &'map self,
+    ) -> impl Iterator<Item = (ScopedSymbolId, BindingWithConstraintsIterator<'map, 'db>)> + 'map
+    {
+        (0..self.public_symbols.len())
+            .map(ScopedSymbolId::from_usize)
+            .map(|symbol_id| (symbol_id, self.public_bindings(symbol_id)))
+    }
+
     /// This function is intended to be called only once inside `TypeInferenceBuilder::infer_function_body`.
     pub(crate) fn can_implicit_return(&self, db: &dyn crate::Db) -> bool {
         !self

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

@@ -20,8 +20,8 @@ use crate::types::generics::{Specialization, SpecializationBuilder};
 use crate::types::signatures::{Parameter, ParameterForm};
 use crate::types::{
     BoundMethodType, DataclassParams, DataclassTransformerParams, FunctionDecorators, KnownClass,
-    KnownFunction, KnownInstanceType, MethodWrapperKind, PropertyInstanceType, UnionType,
+    KnownFunction, KnownInstanceType, MethodWrapperKind, PropertyInstanceType, TupleType,
-    WrapperDescriptorKind,
+    UnionType, WrapperDescriptorKind,
 };
 use ruff_db::diagnostic::{Annotation, Severity, Span, SubDiagnostic};
 use ruff_python_ast as ast;
@@ -561,6 +561,22 @@ 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
+                                        .protocol_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::{
@@ -1710,6 +1712,11 @@ 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> {
@@ -1721,6 +1728,125 @@ 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> {
+    /// Returns the protocol members of this class.
+    ///
+    /// A protocol's members define the interface declared by the protocol.
+    /// They therefore determine how the protocol should behave with regards to
+    /// assignability and subtyping.
+    ///
+    /// The list of members consists of all bindings and declarations that take place
+    /// in the protocol's class body, except for a list of excluded attributes which should
+    /// not be taken into account. (This list includes `__init__` and `__new__`, which can
+    /// legally be defined on protocol classes but do not constitute protocol members.)
+    ///
+    /// It is illegal for a protocol class to have any instance attributes that are not declared
+    /// in the protocol's class body. If any are assigned to, they are not taken into account in
+    /// the protocol's list of members.
+    pub(super) fn protocol_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_protocol_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))
+            {
+                let parent_scope = parent_protocol.body_scope(db);
+                let use_def_map = use_def_map(db, parent_scope);
+                let symbol_table = symbol_table(db, parent_scope);
+
+                members.extend(
+                    use_def_map
+                        .all_public_declarations()
+                        .flat_map(|(symbol_id, declarations)| {
+                            symbol_from_declarations(db, declarations)
+                                .map(|symbol| (symbol_id, symbol))
+                        })
+                        .filter_map(|(symbol_id, symbol)| {
+                            symbol.symbol.ignore_possibly_unbound().map(|_| symbol_id)
+                        })
+                        // Bindings in the class body that are not declared in the class body
+                        // are not valid protocol members, and we plan to emit diagnostics for them
+                        // elsewhere. Invalid or not, however, it's important that we still consider
+                        // them to be protocol members. The implementation of `issubclass()` and
+                        // `isinstance()` for runtime-checkable protocols considers them to be protocol
+                        // members at runtime, and it's important that we accurately understand
+                        // type narrowing that uses `isinstance()` or `issubclass()` with
+                        // runtime-checkable protocols.
+                        .chain(use_def_map.all_public_bindings().filter_map(
+                            |(symbol_id, bindings)| {
+                                symbol_from_bindings(db, bindings)
+                                    .ignore_possibly_unbound()
+                                    .map(|_| symbol_id)
+                            },
+                        ))
+                        .map(|symbol_id| symbol_table.symbol(symbol_id).name())
+                        .filter(|name| !excluded_from_proto_members(name))
+                        .cloned(),
+                );
+            }
+
+            members.sort();
+            members.into_boxed_slice()
+        }
+
+        cached_protocol_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.