address review

Author: AlexWaygood

crates/ty_python_semantic/resources/mdtest/call/function.md

@@ -724,14 +724,14 @@ def f3(coinflip: bool):
 
 def f4(a=None, b=None, c=None, d=None, e=None): ...
 
-my_args = (("a", "b"), ("c", "d"), ("e", "f"))
+my_args = ((1, 2), (3, 4), (5, 6))
 
 for tup in my_args:
     f4(*tup, e=None)  # fine
 
 my_other_args = (
-    ("a", "b", "c", "d", "e"),
-    ("f", "g", "h", "i", "k"),
+    (1, 2, 3, 4, 5),
+    (6, 7, 8, 9, 10),
 )
 
 for tup in my_other_args:

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

@@ -2313,6 +2313,12 @@ impl<'a, 'db> ArgumentMatcher<'a, 'db> {
         argument: Argument<'a>,
         argument_type: Option<Type<'db>>,
     ) -> Result<(), ()> {
+        // TODO: `Type::iterate` internally handles unions, but in a lossy way.
+        // It might be superior here to manually map over the union and call `try_iterate`
+        // on each element, similar to the way that `unpacker.rs` does in the `unpack_inner` method.
+        // It might be a bit of a refactor, though.
+        // See <https://github.com/astral-sh/ruff/pull/20377#issuecomment-3401380305>
+        // for more details. --Alex
         let tuple = argument_type.map(|ty| ty.iterate(db));
         let (mut argument_types, length, variable_element) = match tuple.as_ref() {
             Some(tuple) => (

crates/ty_python_semantic/src/types/unpacker.rs

@@ -118,6 +118,11 @@ impl<'db, 'ast> Unpacker<'db, 'ast> {
                 };
                 let mut unpacker = TupleUnpacker::new(self.db(), target_len);
 
+                // N.B. `Type::try_iterate` internally handles unions, but in a lossy way.
+                // For our purposes here, we get better error messages and more precise inference
+                // if we manually map over the union and call `try_iterate` on each union element.
+                // See <https://github.com/astral-sh/ruff/pull/20377#issuecomment-3401380305>
+                // for more discussion.
                 let unpack_types = match value_ty {
                     Type::Union(union_ty) => union_ty.elements(self.db()),
                     _ => std::slice::from_ref(&value_ty),