[red-knot] Recurse into the types of protocol members when normalizing a protocol's interface (#17808)

## Summary

Currently red-knot does not understand `Foo` and `Bar` here as being
equivalent:

```py
from typing import Protocol

class A: ...
class B: ...
class C: ...

class Foo(Protocol):
    x: A | B | C

class Bar(Protocol):
    x: B | A | C
```

Nor does it understand `A | B | Foo` as being equivalent to `Bar | B |
A`. This PR fixes that.

## Test Plan

new mdtest assertions added that fail on `main`

crates/red_knot_python_semantic/resources/mdtest/protocols.md

@@ -816,6 +816,22 @@ class B: ...
 static_assert(is_equivalent_to(A | HasX | B | HasY, B | AlsoHasY | AlsoHasX | A))
 ```
 
+Protocols are considered equivalent if their members are equivalent, even if those members are
+differently ordered unions:
+
+```py
+class C: ...
+
+class UnionProto1(Protocol):
+    x: A | B | C
+
+class UnionProto2(Protocol):
+    x: C | A | B
+
+static_assert(is_equivalent_to(UnionProto1, UnionProto2))
+static_assert(is_equivalent_to(UnionProto1 | A | B, B | UnionProto2 | A))
+```
+
 ## Intersections of protocols
 
 An intersection of two protocol types `X` and `Y` is equivalent to a protocol type `Z` that inherits

crates/red_knot_python_semantic/src/types/instance.rs

@@ -5,6 +5,8 @@ use super::{ClassType, KnownClass, SubclassOfType, Type};
 use crate::symbol::{Symbol, SymbolAndQualifiers};
 use crate::Db;
 
+pub(super) use synthesized_protocol::SynthesizedProtocolType;
+
 impl<'db> Type<'db> {
     pub(crate) fn instance(db: &'db dyn Db, class: ClassType<'db>) -> Self {
         if class.class_literal(db).0.is_protocol(db) {
@@ -164,7 +166,7 @@ impl<'db> ProtocolInstanceType<'db> {
         }
         match self.0 {
             Protocol::FromClass(_) => Type::ProtocolInstance(Self(Protocol::Synthesized(
-                SynthesizedProtocolType::new(db, self.0.interface(db)),
+                SynthesizedProtocolType::new(db, self.0.interface(db).clone()),
             ))),
             Protocol::Synthesized(_) => Type::ProtocolInstance(self),
         }
@@ -237,9 +239,7 @@ impl<'db> ProtocolInstanceType<'db> {
 
 /// An enumeration of the two kinds of protocol types: those that originate from a class
 /// definition in source code, and those that are synthesized from a set of members.
-#[derive(
-    Copy, Clone, Debug, Eq, PartialEq, Hash, salsa::Update, salsa::Supertype, PartialOrd, Ord,
-)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash, salsa::Update, PartialOrd, Ord)]
 pub(super) enum Protocol<'db> {
     FromClass(ClassType<'db>),
     Synthesized(SynthesizedProtocolType<'db>),
@@ -260,14 +260,38 @@ impl<'db> Protocol<'db> {
     }
 }
 
-/// A "synthesized" protocol type that is dissociated from a class definition in source code.
-///
-/// Two synthesized protocol types with the same members will share the same Salsa ID,
-/// making them easy to compare for equivalence. A synthesized protocol type is therefore
-/// returned by [`ProtocolInstanceType::normalized`] so that two protocols with the same members
-/// will be understood as equivalent even in the context of differently ordered unions or intersections.
-#[salsa::interned(debug)]
-pub(super) struct SynthesizedProtocolType<'db> {
-    #[return_ref]
-    pub(super) interface: ProtocolInterface<'db>,
+mod synthesized_protocol {
+    use crate::db::Db;
+    use crate::types::protocol_class::ProtocolInterface;
+
+    /// A "synthesized" protocol type that is dissociated from a class definition in source code.
+    ///
+    /// Two synthesized protocol types with the same members will share the same Salsa ID,
+    /// making them easy to compare for equivalence. A synthesized protocol type is therefore
+    /// returned by [`super::ProtocolInstanceType::normalized`] so that two protocols with the same members
+    /// will be understood as equivalent even in the context of differently ordered unions or intersections.
+    ///
+    /// The constructor method of this type maintains the invariant that a synthesized protocol type
+    /// is always constructed from a *normalized* protocol interface.
+    #[derive(Copy, Clone, Debug, Eq, PartialEq, Hash, salsa::Update, PartialOrd, Ord)]
+    pub(in crate::types) struct SynthesizedProtocolType<'db>(SynthesizedProtocolTypeInner<'db>);
+
+    impl<'db> SynthesizedProtocolType<'db> {
+        pub(super) fn new(db: &'db dyn Db, interface: ProtocolInterface<'db>) -> Self {
+            Self(SynthesizedProtocolTypeInner::new(
+                db,
+                interface.normalized(db),
+            ))
+        }
+
+        pub(in crate::types) fn interface(self, db: &'db dyn Db) -> &'db ProtocolInterface<'db> {
+            self.0.interface(db)
+        }
+    }
+
+    #[salsa::interned(debug)]
+    struct SynthesizedProtocolTypeInner<'db> {
+        #[return_ref]
+        interface: ProtocolInterface<'db>,
+    }
 }

crates/red_knot_python_semantic/src/types/protocol_class.rs

@@ -96,6 +96,15 @@ impl<'db> ProtocolInterface<'db> {
     pub(super) fn contains_todo(&self, db: &'db dyn Db) -> bool {
         self.members().any(|member| member.ty.contains_todo(db))
     }
+
+    pub(super) fn normalized(self, db: &'db dyn Db) -> Self {
+        Self(
+            self.0
+                .into_iter()
+                .map(|(name, data)| (name, data.normalized(db)))
+                .collect(),
+        )
+    }
 }
 
 #[derive(Debug, PartialEq, Eq, Clone, Hash, salsa::Update)]
@@ -104,6 +113,15 @@ struct ProtocolMemberData<'db> {
     qualifiers: TypeQualifiers,
 }
 
+impl<'db> ProtocolMemberData<'db> {
+    fn normalized(self, db: &'db dyn Db) -> Self {
+        Self {
+            ty: self.ty.normalized(db),
+            qualifiers: self.qualifiers,
+        }
+    }
+}
+
 /// A single member of a protocol interface.
 #[derive(Debug, PartialEq, Eq)]
 pub(super) struct ProtocolMember<'a, 'db> {