From 9360adccda17f3236a93514a44f8c57b0be4c890 Mon Sep 17 00:00:00 2001
From: Ryo Yoshida <low.ryoshida@gmail.com>
Date: Sun, 7 May 2023 01:31:36 +0900
Subject: [PATCH] Ignore impls with `#[rustc_reservation_impl]`

---
 crates/hir-ty/src/chalk_db.rs          |  2 +-
 crates/hir-ty/src/method_resolution.rs |  9 +++++++++
 crates/hir-ty/src/tests/never_type.rs  | 19 +++++++++++++++++++
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/crates/hir-ty/src/chalk_db.rs b/crates/hir-ty/src/chalk_db.rs
index d68703ce1d47c..983cc22212421 100644
--- a/crates/hir-ty/src/chalk_db.rs
+++ b/crates/hir-ty/src/chalk_db.rs
@@ -453,7 +453,7 @@ impl<'a> chalk_solve::RustIrDatabase<Interner> for ChalkContext<'a> {
     }
 }
 
-impl<'a> chalk_ir::UnificationDatabase<Interner> for &'a dyn HirDatabase {
+impl chalk_ir::UnificationDatabase<Interner> for &dyn HirDatabase {
     fn fn_def_variance(
         &self,
         fn_def_id: chalk_ir::FnDefId<Interner>,
diff --git a/crates/hir-ty/src/method_resolution.rs b/crates/hir-ty/src/method_resolution.rs
index 912efc3a89605..8d57211db0778 100644
--- a/crates/hir-ty/src/method_resolution.rs
+++ b/crates/hir-ty/src/method_resolution.rs
@@ -187,6 +187,15 @@ impl TraitImpls {
     fn collect_def_map(&mut self, db: &dyn HirDatabase, def_map: &DefMap) {
         for (_module_id, module_data) in def_map.modules() {
             for impl_id in module_data.scope.impls() {
+                // Reservation impls should be ignored during trait resolution, so we never need
+                // them during type analysis. See rust-lang/rust#64631 for details.
+                //
+                // FIXME: Reservation impls should be considered during coherence checks. If we are
+                // (ever) to implement coherence checks, this filtering should be done by the trait
+                // solver.
+                if db.attrs(impl_id.into()).by_key("rustc_reservation_impl").exists() {
+                    continue;
+                }
                 let target_trait = match db.impl_trait(impl_id) {
                     Some(tr) => tr.skip_binders().hir_trait_id(),
                     None => continue,
diff --git a/crates/hir-ty/src/tests/never_type.rs b/crates/hir-ty/src/tests/never_type.rs
index fbdc8209f8f4b..09c63f873ee62 100644
--- a/crates/hir-ty/src/tests/never_type.rs
+++ b/crates/hir-ty/src/tests/never_type.rs
@@ -483,3 +483,22 @@ fn example() -> bool {
 "#,
     );
 }
+
+#[test]
+fn reservation_impl_should_be_ignored() {
+    // See rust-lang/rust#64631.
+    check_types(
+        r#"
+//- minicore: from
+struct S;
+#[rustc_reservation_impl]
+impl<T> From<!> for T {}
+fn foo<T, U: From<T>>(_: U) -> T { loop {} }
+
+fn test() {
+    let s = foo(S);
+      //^ S
+}
+"#,
+    );
+}