[ty] Followups to tuple constructor improvements in astral-sh#18987 (astral-sh#19000)

Author: AlexWaygood

crates/ty_python_semantic/src/types.rs

@@ -4247,6 +4247,13 @@ impl<'db> Type<'db> {
                 Some(KnownClass::Tuple) => {
                     let object = Type::object(db);
 
+                    // ```py
+                    // class tuple:
+                    //     @overload
+                    //     def __new__(cls) -> tuple[()]: ...
+                    //     @overload
+                    //     def __new__(cls, iterable: Iterable[object]) -> tuple[object, ...]: ...
+                    // ```
                     CallableBinding::from_overloads(
                         self,
                         [
@@ -4308,6 +4315,13 @@ impl<'db> Type<'db> {
                 let instantiated = Type::instance(db, ClassType::from(alias));
 
                 let parameters = if alias.origin(db).is_known(db, KnownClass::Tuple) {
+                    // ```py
+                    // class tuple:
+                    //     @overload
+                    //     def __new__(cls: type[tuple[()]], iterable: tuple[()] = ()) -> tuple[()]: ...
+                    //     @overload
+                    //     def __new__[T](cls: type[tuple[T, ...]], iterable: tuple[T, ...]) -> tuple[T, ...]: ...
+                    // ```
                     let spec = alias.specialization(db).tuple(db);
                     let mut parameter =
                         Parameter::positional_only(Some(Name::new_static("iterable")))

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

@@ -973,13 +973,16 @@ impl<'db> Bindings<'db> {
                         }
 
                         Some(KnownClass::Tuple) if overload_index == 1 => {
+                            // `tuple(range(42))` => `tuple[int, ...]`
+                            // BUT `tuple((1, 2))` => `tuple[Literal[1], Literal[2]]` rather than `tuple[Literal[1, 2], ...]`
                             if let [Some(argument)] = overload.parameter_types() {
                                 let overridden_return =
                                     argument.into_tuple().map(Type::Tuple).unwrap_or_else(|| {
                                         // Some awkward special handling is required here because of the fact
                                         // that calling `try_iterate()` on `Never` returns `Never`,
                                         // but `tuple[Never, ...]` eagerly simplifies to `tuple[()]`,
-                                        // which will cause us to emit false positives if we index into the tuple
+                                        // which will cause us to emit false positives if we index into the tuple.
+                                        // Using `tuple[Unknown, ...]` avoids these false positives.
                                         let specialization = if argument.is_never() {
                                             Type::unknown()
                                         } else {

crates/ty_python_semantic/src/types/class.rs

@@ -2427,7 +2427,7 @@ impl KnownClass {
             | Self::Float
             | Self::Enum
             | Self::ABCMeta
-            | KnownClass::Iterable
+            | Self::Iterable
             // Empty tuples are AlwaysFalse; non-empty tuples are AlwaysTrue
             | Self::NamedTuple
             // Evaluating `NotImplementedType` in a boolean context was deprecated in Python 3.9