From 340f0fc3334f11b30f4c55757a0acb0b76ac5e37 Mon Sep 17 00:00:00 2001
From: Florian Diebold <flodiebold@gmail.com>
Date: Fri, 8 Apr 2022 14:29:43 +0200
Subject: [PATCH] Ignore `Drop` and `Destruct` bounds for now

- `T: ~const Drop` has a special meaning in Rust 1.61 that we don't implement.
  (So ideally, we'd only ignore `~const Drop`, but this should be fine
  for now.)
- `Destruct` impls are built-in in 1.62 (current nightlies as of 08-04-2022), so until
  the builtin impls are supported by Chalk, we ignore them as well.
  Since `Destruct` is implemented for everything in non-const contexts
  IIUC, this should also work fine.

Fixes #11932.
---
 crates/hir_ty/src/lower.rs            | 19 ++++++-
 crates/hir_ty/src/tests/regression.rs | 79 +++++++++++++++++++++++++++
 2 files changed, 97 insertions(+), 1 deletion(-)

diff --git a/crates/hir_ty/src/lower.rs b/crates/hir_ty/src/lower.rs
index ca6241c5d1a..24eff4cc9a9 100644
--- a/crates/hir_ty/src/lower.rs
+++ b/crates/hir_ty/src/lower.rs
@@ -14,6 +14,7 @@ use chalk_ir::interner::HasInterner;
 use chalk_ir::{cast::Cast, fold::Shift, Mutability, Safety};
 use hir_def::generics::TypeOrConstParamData;
 use hir_def::intern::Interned;
+use hir_def::lang_item::lang_attr;
 use hir_def::path::{ModPath, PathKind};
 use hir_def::type_ref::ConstScalarOrPath;
 use hir_def::{
@@ -863,7 +864,23 @@ impl<'a> TyLoweringContext<'a> {
         let trait_ref = match bound {
             TypeBound::Path(path, TraitBoundModifier::None) => {
                 bindings = self.lower_trait_ref_from_path(path, Some(self_ty));
-                bindings.clone().map(WhereClause::Implemented).map(crate::wrap_empty_binders)
+                bindings
+                    .clone()
+                    .filter(|tr| {
+                        // ignore `T: Drop` or `T: Destruct` bounds.
+                        // - `T: ~const Drop` has a special meaning in Rust 1.61 that we don't implement.
+                        //   (So ideally, we'd only ignore `~const Drop` here)
+                        // - `Destruct` impls are built-in in 1.62 (current nightlies as of 08-04-2022), so until
+                        //   the builtin impls are supported by Chalk, we ignore them here.
+                        if let Some(lang) = lang_attr(self.db.upcast(), tr.hir_trait_id()) {
+                            if lang == "drop" || lang == "destruct" {
+                                return false;
+                            }
+                        }
+                        true
+                    })
+                    .map(WhereClause::Implemented)
+                    .map(crate::wrap_empty_binders)
             }
             TypeBound::Path(path, TraitBoundModifier::Maybe) => {
                 let sized_trait = self
diff --git a/crates/hir_ty/src/tests/regression.rs b/crates/hir_ty/src/tests/regression.rs
index 37f321a0f00..a02ec6f85c6 100644
--- a/crates/hir_ty/src/tests/regression.rs
+++ b/crates/hir_ty/src/tests/regression.rs
@@ -1505,3 +1505,82 @@ fn f(s: S) {
 "#,
     );
 }
+
+#[test]
+fn rust_161_option_clone() {
+    check_types(
+        r#"
+//- minicore: option, drop
+
+fn test(o: &Option<i32>) {
+    o.my_clone();
+  //^^^^^^^^^^^^ Option<i32>
+}
+
+pub trait MyClone: Sized {
+    fn my_clone(&self) -> Self;
+}
+
+impl<T> const MyClone for Option<T>
+where
+    T: ~const MyClone + ~const Drop + ~const Destruct,
+{
+    fn my_clone(&self) -> Self {
+        match self {
+            Some(x) => Some(x.my_clone()),
+            None => None,
+        }
+    }
+}
+
+impl const MyClone for i32 {
+    fn my_clone(&self) -> Self {
+        *self
+    }
+}
+
+pub trait Destruct {}
+
+impl<T: ?Sized> const Destruct for T {}
+"#,
+    );
+}
+
+#[test]
+fn rust_162_option_clone() {
+    check_types(
+        r#"
+//- minicore: option, drop
+
+fn test(o: &Option<i32>) {
+    o.my_clone();
+  //^^^^^^^^^^^^ Option<i32>
+}
+
+pub trait MyClone: Sized {
+    fn my_clone(&self) -> Self;
+}
+
+impl<T> const MyClone for Option<T>
+where
+    T: ~const MyClone + ~const Destruct,
+{
+    fn my_clone(&self) -> Self {
+        match self {
+            Some(x) => Some(x.my_clone()),
+            None => None,
+        }
+    }
+}
+
+impl const MyClone for i32 {
+    fn my_clone(&self) -> Self {
+        *self
+    }
+}
+
+#[lang = "destruct"]
+pub trait Destruct {}
+"#,
+    );
+}