[ty] Remove use of ClassBase::try_from_type from super() machinery

Author: AlexWaygood

crates/ty_python_semantic/resources/mdtest/class/super.md

@@ -331,6 +331,9 @@ instance or a subclass of the first. If either condition is violated, a `TypeErr
 runtime.
 
 ```py
+import typing
+import collections
+
 def f(x: int):
     # error: [invalid-super-argument] "`int` is not a valid class"
     super(x, x)
@@ -367,6 +370,16 @@ reveal_type(super(B, A))
 reveal_type(super(B, object))
 
 super(object, object()).__class__
+
+# Not all objects valid in a class's bases list are valid as the first argument to `super()`.
+# For example, it's valid to inherit from `typing.ChainMap`, but it's not valid as the first argument to `super()`.
+#
+# error: [invalid-super-argument] "`typing.ChainMap` is not a valid class"
+reveal_type(super(typing.ChainMap, collections.ChainMap()))  # revealed: Unknown
+
+# Meanwhile, it's not valid to inherit from unsubscripted `typing.Generic`,
+# but it *is* valid as the first argument to `super()`.
+reveal_type(super(typing.Generic, typing.SupportsInt))  # revealed: <super: typing.Generic, <class 'SupportsInt'>>
 ```
 
 ### Instance Member Access via `super`

crates/ty_python_semantic/src/types.rs

@@ -9389,23 +9389,24 @@ impl<'db> BoundSuperType<'db> {
             ));
         }
 
-        // TODO: having to get a class-literal just to pass it in here is silly.
-        // `BoundSuperType` should probably not be using `ClassBase::try_from_type` here;
-        // this also leads to false negatives in some cases. See discussion in
-        // <https://github.com/astral-sh/ruff/pull/19560#discussion_r2271570071>.
-        let pivot_class = ClassBase::try_from_type(
-            db,
-            pivot_class_type,
-            KnownClass::Object
-                .to_class_literal(db)
-                .into_class_literal()
-                .expect("`object` should always exist in typeshed"),
-        )
-        .ok_or({
-            BoundSuperError::InvalidPivotClassType {
-                pivot_class: pivot_class_type,
+        // We don't use `Classbase::try_from_type` here because:
+        // - There are objects that may validly be present in a class's bases list
+        //   but are not valid as pivot classes, e.g. `typing.ChainMap`
+        // - There are objects that are not valid in a class's bases list
+        //   but are valid as pivot classes, e.g. unsubscripted `typing.Generic`
+        let pivot_class = match pivot_class_type {
+            Type::ClassLiteral(class) => ClassBase::Class(ClassType::NonGeneric(class)),
+            Type::GenericAlias(class) => ClassBase::Class(ClassType::Generic(class)),
+            Type::SpecialForm(SpecialFormType::Protocol) => ClassBase::Protocol,
+            Type::SpecialForm(SpecialFormType::Generic) => ClassBase::Generic,
+            Type::SpecialForm(SpecialFormType::TypedDict) => ClassBase::TypedDict,
+            Type::Dynamic(dynamic) => ClassBase::Dynamic(dynamic),
+            _ => {
+                return Err(BoundSuperError::InvalidPivotClassType {
+                    pivot_class: pivot_class_type,
+                });
             }
-        })?;
+        };
 
         let owner = SuperOwnerKind::try_from_type(db, owner_type)
             .and_then(|owner| {