From ef45c97dab2e1ab8268308a53e6dd452db40b0db Mon Sep 17 00:00:00 2001
From: Charlie Marsh <charlie.r.marsh@gmail.com>
Date: Fri, 5 Dec 2025 11:04:23 -0800
Subject: [PATCH] [ty] Allow `tuple[Any, ...]` to assign to `tuple[int,
 *tuple[int, ...]]` (#21803)

## Summary

Closes https://github.com/astral-sh/ty/issues/1750.
---
 .../type_properties/is_assignable_to.md       | 10 ++++++
 crates/ty_python_semantic/src/types/tuple.rs  | 36 +++++++++++++++----
 2 files changed, 40 insertions(+), 6 deletions(-)

diff --git a/crates/ty_python_semantic/resources/mdtest/type_properties/is_assignable_to.md b/crates/ty_python_semantic/resources/mdtest/type_properties/is_assignable_to.md
index 3bd3cd1f09..f9f85641f7 100644
--- a/crates/ty_python_semantic/resources/mdtest/type_properties/is_assignable_to.md
+++ b/crates/ty_python_semantic/resources/mdtest/type_properties/is_assignable_to.md
@@ -537,6 +537,9 @@ static_assert(is_assignable_to(tuple[Any, ...], tuple[Any, Any]))
 static_assert(is_assignable_to(tuple[Any, ...], tuple[int, ...]))
 static_assert(is_assignable_to(tuple[Any, ...], tuple[int]))
 static_assert(is_assignable_to(tuple[Any, ...], tuple[int, int]))
+static_assert(is_assignable_to(tuple[Any, ...], tuple[int, *tuple[int, ...]]))
+static_assert(is_assignable_to(tuple[Any, ...], tuple[*tuple[int, ...], int]))
+static_assert(is_assignable_to(tuple[Any, ...], tuple[int, *tuple[int, ...], int]))
 ```
 
 This also applies when `tuple[Any, ...]` is unpacked into a mixed tuple.
@@ -560,6 +563,10 @@ static_assert(is_assignable_to(tuple[*tuple[Any, ...], int], tuple[int, ...]))
 static_assert(is_assignable_to(tuple[*tuple[Any, ...], int], tuple[int]))
 static_assert(is_assignable_to(tuple[*tuple[Any, ...], int], tuple[int, int]))
 
+# `*tuple[Any, ...]` can materialize to a tuple of any length as a special case,
+# so this passes:
+static_assert(is_assignable_to(tuple[*tuple[Any, ...], Any], tuple[*tuple[Any, ...], Any, Any]))
+
 static_assert(is_assignable_to(tuple[int, *tuple[Any, ...], int], tuple[int, *tuple[Any, ...], int]))
 static_assert(is_assignable_to(tuple[int, *tuple[Any, ...], int], tuple[Any, ...]))
 static_assert(not is_assignable_to(tuple[int, *tuple[Any, ...], int], tuple[Any]))
@@ -580,6 +587,9 @@ static_assert(not is_assignable_to(tuple[int, ...], tuple[Any, Any]))
 static_assert(is_assignable_to(tuple[int, ...], tuple[int, ...]))
 static_assert(not is_assignable_to(tuple[int, ...], tuple[int]))
 static_assert(not is_assignable_to(tuple[int, ...], tuple[int, int]))
+static_assert(not is_assignable_to(tuple[int, ...], tuple[int, *tuple[int, ...]]))
+static_assert(not is_assignable_to(tuple[int, ...], tuple[*tuple[int, ...], int]))
+static_assert(not is_assignable_to(tuple[int, ...], tuple[int, *tuple[int, ...], int]))
 
 static_assert(is_assignable_to(tuple[int, *tuple[int, ...]], tuple[int, *tuple[Any, ...]]))
 static_assert(is_assignable_to(tuple[int, *tuple[int, ...]], tuple[Any, ...]))
diff --git a/crates/ty_python_semantic/src/types/tuple.rs b/crates/ty_python_semantic/src/types/tuple.rs
index 787bbe0688..9b046cd4cf 100644
--- a/crates/ty_python_semantic/src/types/tuple.rs
+++ b/crates/ty_python_semantic/src/types/tuple.rs
@@ -998,10 +998,22 @@ impl<'db> VariableLengthTuple<Type<'db>> {
                             relation_visitor,
                             disjointness_visitor,
                         ),
-                        EitherOrBoth::Right(_) => {
+                        EitherOrBoth::Right(other_ty) => {
                             // The rhs has a required element that the lhs is not guaranteed to
-                            // provide.
-                            return ConstraintSet::from(false);
+                            // provide, unless the lhs has a dynamic variable-length portion
+                            // that can materialize to provide it (for assignability only),
+                            // as in `tuple[Any, ...]` matching `tuple[int, int]`.
+                            if !relation.is_assignability() || !self.variable.is_dynamic() {
+                                return ConstraintSet::from(false);
+                            }
+                            self.variable.has_relation_to_impl(
+                                db,
+                                other_ty,
+                                inferable,
+                                relation,
+                                relation_visitor,
+                                disjointness_visitor,
+                            )
                         }
                     };
                     if result
@@ -1037,10 +1049,22 @@ impl<'db> VariableLengthTuple<Type<'db>> {
                             relation_visitor,
                             disjointness_visitor,
                         ),
-                        EitherOrBoth::Right(_) => {
+                        EitherOrBoth::Right(other_ty) => {
                             // The rhs has a required element that the lhs is not guaranteed to
-                            // provide.
-                            return ConstraintSet::from(false);
+                            // provide, unless the lhs has a dynamic variable-length portion
+                            // that can materialize to provide it (for assignability only),
+                            // as in `tuple[Any, ...]` matching `tuple[int, int]`.
+                            if !relation.is_assignability() || !self.variable.is_dynamic() {
+                                return ConstraintSet::from(false);
+                            }
+                            self.variable.has_relation_to_impl(
+                                db,
+                                *other_ty,
+                                inferable,
+                                relation,
+                                relation_visitor,
+                                disjointness_visitor,
+                            )
                         }
                     };
                     if result