From 019ec37db09d9f4bcb4a87fef4dde5b06b424d1e Mon Sep 17 00:00:00 2001
From: Ryo Yoshida <low.ryoshida@gmail.com>
Date: Thu, 16 Feb 2023 18:45:37 +0900
Subject: [PATCH 1/3] Fix projection substitution order considering GATs

---
 chalk-solve/src/clauses.rs | 11 ++++++-----
 tests/test/projection.rs   | 24 ++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/chalk-solve/src/clauses.rs b/chalk-solve/src/clauses.rs
index e3fdd351b7a..a0ede39df7c 100644
--- a/chalk-solve/src/clauses.rs
+++ b/chalk-solve/src/clauses.rs
@@ -820,13 +820,14 @@ fn push_alias_alias_eq_clause<I: Interner>(
         //      <<X as Y>::A as Z>::B == U :- <T as Z>::B == U, <X as Y>::A == T
         // }
         builder.push_binders(binders, |builder, bound_var| {
+            let (_, trait_args, assoc_args) = builder.db.split_projection(&projection_ty);
             let fresh_self_subst = Substitution::from_iter(
                 interner,
-                std::iter::once(bound_var.clone().cast(interner)).chain(
-                    projection_ty.substitution.as_slice(interner)[1..]
-                        .iter()
-                        .cloned(),
-                ),
+                assoc_args
+                    .iter()
+                    .cloned()
+                    .chain(std::iter::once(bound_var.clone().cast(interner)))
+                    .chain(trait_args[1..].iter().cloned()),
             );
             let fresh_alias = AliasTy::Projection(ProjectionTy {
                 associated_ty_id: projection_ty.associated_ty_id,
diff --git a/tests/test/projection.rs b/tests/test/projection.rs
index a98a660dfed..021aba29972 100644
--- a/tests/test/projection.rs
+++ b/tests/test/projection.rs
@@ -609,6 +609,30 @@ fn normalize_gat_with_higher_ranked_trait_bound() {
     }
 }
 
+#[test]
+fn gat_in_alias_in_alias_eq() {
+    test! {
+        program {
+            trait Foo {
+                type Rebind<U>: Foo;
+            }
+
+            struct S<T> { }
+            impl<T> Foo for S<T> {
+                type Rebind<U> = S<U>;
+            }
+        }
+
+        goal {
+            exists<T> {
+                <<S<u32> as Foo>::Rebind<i32> as Foo>::Rebind<usize>: Foo
+            }
+        } yields {
+            expect![[r#"Unique"#]]
+        }
+    }
+}
+
 #[test]
 fn forall_projection() {
     test! {

From 6ef68c9f5c8164a09d275a70fb1cc689eb2be0f7 Mon Sep 17 00:00:00 2001
From: Ryo Yoshida <low.ryoshida@gmail.com>
Date: Thu, 16 Feb 2023 18:46:38 +0900
Subject: [PATCH 2/3] Unignore doctest for GATs

---
 chalk-solve/src/rust_ir.rs | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/chalk-solve/src/rust_ir.rs b/chalk-solve/src/rust_ir.rs
index 935a29032da..62861876515 100644
--- a/chalk-solve/src/rust_ir.rs
+++ b/chalk-solve/src/rust_ir.rs
@@ -214,11 +214,10 @@ pub struct FnDefDatumBound<I: Interner> {
 }
 
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
-// FIXME: unignore the doctest below when GATs hit stable.
 /// A rust intermediate representation (rust_ir) of a Trait Definition. For
 /// example, given the following rust code:
 ///
-/// ```ignore
+/// ```
 /// use std::fmt::Debug;
 ///
 /// trait Foo<T>

From aa036e6c3b654dd7062aa0e4c2893118f4234bf0 Mon Sep 17 00:00:00 2001
From: Ryo Yoshida <low.ryoshida@gmail.com>
Date: Thu, 16 Feb 2023 19:42:12 +0900
Subject: [PATCH 3/3] Update link to rustc's `TyKind`

---
 book/src/types/rust_types.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/book/src/types/rust_types.md b/book/src/types/rust_types.md
index d96c234f3b9..45359ff0d07 100644
--- a/book/src/types/rust_types.md
+++ b/book/src/types/rust_types.md
@@ -168,7 +168,7 @@ types. The intention is that, at least when transitioning, rustc would
 implement the `Interner` trait and would map from the [`TyKind`][Rustc-TyKind]
 enum to chalk's [`TyKind`] on the fly, when `data()` is invoked.
 
-[Rustc-TyKind]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/enum.TyKind.html
+[Rustc-TyKind]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_type_ir/sty/enum.TyKind.html
 
 | rustc type | chalk variant (and some notes) |
 | ------------- | ------------------ |