From b217e9cc50a5fb3a85f4db162b3217e4e7f007c5 Mon Sep 17 00:00:00 2001
From: Dawer <7803845+iDawer@users.noreply.github.com>
Date: Sat, 12 Jun 2021 21:47:07 +0500
Subject: [PATCH] add implicit Sized bound to associated types

---
 crates/hir_ty/src/chalk_db.rs                | 17 ++++++++++-
 crates/hir_ty/src/lower.rs                   |  7 ++---
 crates/hir_ty/src/tests/method_resolution.rs | 28 +++++++++++++++++
 crates/hir_ty/src/tests/traits.rs            | 32 ++++++++++++++++++++
 4 files changed, 79 insertions(+), 5 deletions(-)

diff --git a/crates/hir_ty/src/chalk_db.rs b/crates/hir_ty/src/chalk_db.rs
index a55b99de042..333d934ed37 100644
--- a/crates/hir_ty/src/chalk_db.rs
+++ b/crates/hir_ty/src/chalk_db.rs
@@ -412,13 +412,28 @@ pub(crate) fn associated_ty_data_query(
         .with_type_param_mode(crate::lower::TypeParamLoweringMode::Variable);
     let self_ty =
         TyKind::BoundVar(BoundVar::new(crate::DebruijnIndex::INNERMOST, 0)).intern(&Interner);
-    let bounds = type_alias_data
+    let mut bounds: Vec<_> = type_alias_data
         .bounds
         .iter()
         .flat_map(|bound| ctx.lower_type_bound(bound, self_ty.clone(), false))
         .filter_map(|pred| generic_predicate_to_inline_bound(db, &pred, &self_ty))
         .collect();
 
+    if !ctx.unsized_types.borrow().contains(&self_ty) {
+        let sized_trait = resolver
+            .krate()
+            .and_then(|krate| db.lang_item(krate, "sized".into()))
+            .and_then(|lang_item| lang_item.as_trait().map(to_chalk_trait_id));
+        let sized_bound = sized_trait.into_iter().map(|sized_trait| {
+            let trait_bound =
+                rust_ir::TraitBound { trait_id: sized_trait, args_no_self: Default::default() };
+            let inline_bound = rust_ir::InlineBound::TraitBound(trait_bound);
+            chalk_ir::Binders::empty(&Interner, inline_bound)
+        });
+        bounds.extend(sized_bound);
+        bounds.shrink_to_fit();
+    }
+
     // FIXME: Re-enable where clauses on associated types when an upstream chalk bug is fixed.
     //        (rust-analyzer#9052)
     // let where_clauses = convert_where_clauses(db, type_alias.into(), &bound_vars);
diff --git a/crates/hir_ty/src/lower.rs b/crates/hir_ty/src/lower.rs
index 3a9e3012319..4544c613893 100644
--- a/crates/hir_ty/src/lower.rs
+++ b/crates/hir_ty/src/lower.rs
@@ -66,8 +66,8 @@ pub struct TyLoweringContext<'a> {
     /// Splitting this up would be a possible fix.
     opaque_type_data: RefCell<Vec<ReturnTypeImplTrait>>,
     expander: RefCell<Option<Expander>>,
-    /// Keeps tracking types with explicit `?Sized` bounds.
-    unsized_types: RefCell<FxHashSet<Ty>>,
+    /// Tracks types with explicit `?Sized` bounds.
+    pub(crate) unsized_types: RefCell<FxHashSet<Ty>>,
 }
 
 impl<'a> TyLoweringContext<'a> {
@@ -796,7 +796,7 @@ pub(crate) fn lower_type_bound(
                     .and_then(|krate| self.db.lang_item(krate, "sized".into()))
                     .and_then(|lang_item| lang_item.as_trait());
                 // Don't lower associated type bindings as the only possible relaxed trait bound
-                // `?Sized` has none of them.
+                // `?Sized` has no of them.
                 // If we got another trait here ignore the bound completely.
                 let trait_id = self
                     .lower_trait_ref_from_path(path, Some(self_ty.clone()))
@@ -996,7 +996,6 @@ pub(crate) fn generic_predicates_for_param_query(
     let ctx =
         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
     let generics = generics(db.upcast(), param_id.parent);
-    // TODO(iDawer): add implicitly sized clauses?
     resolver
         .where_predicates_in_scope()
         // we have to filter out all other predicates *first*, before attempting to lower them
diff --git a/crates/hir_ty/src/tests/method_resolution.rs b/crates/hir_ty/src/tests/method_resolution.rs
index 90eee77422e..aa4234969b9 100644
--- a/crates/hir_ty/src/tests/method_resolution.rs
+++ b/crates/hir_ty/src/tests/method_resolution.rs
@@ -1312,3 +1312,31 @@ fn into_iter(self) -> Self::Out { loop {} }
     "#,
     );
 }
+
+#[test]
+fn sized_blanket_impl() {
+    check_infer(
+        r#"
+#[lang = "sized"]
+pub trait Sized {}
+
+trait Foo { fn foo() -> u8; }
+impl<T: Sized> Foo for T {}
+fn f<S: Sized, T, U: ?Sized>() {
+    u32::foo;
+    S::foo;
+    T::foo;
+    U::foo;
+    <[u32]>::foo;
+}
+"#,
+        expect![[r#"
+            127..198 '{     ...foo; }': ()
+            133..141 'u32::foo': fn foo<u32>() -> u8
+            147..153 'S::foo': fn foo<S>() -> u8
+            159..165 'T::foo': fn foo<T>() -> u8
+            171..177 'U::foo': {unknown}
+            183..195 '<[u32]>::foo': {unknown}
+        "#]],
+    );
+}
diff --git a/crates/hir_ty/src/tests/traits.rs b/crates/hir_ty/src/tests/traits.rs
index d5d0173ec11..dfcc4608c16 100644
--- a/crates/hir_ty/src/tests/traits.rs
+++ b/crates/hir_ty/src/tests/traits.rs
@@ -3515,3 +3515,35 @@ fn foo(&self) -> S1 { S1 }
 "#,
     );
 }
+
+#[test]
+fn associated_type_sized_bounds() {
+    check_infer(
+        r#"
+#[lang = "sized"]
+pub trait Sized {}
+
+struct Yes;
+trait IsSized { const IS_SIZED: Yes; }
+impl<T: Sized> IsSized for T { const IS_SIZED: Yes = Yes; }
+
+trait Foo {
+    type Explicit: Sized;
+    type Implicit;
+    type Relaxed: ?Sized;
+}
+fn f<F: Foo>() {
+    F::Explicit::IS_SIZED;
+    F::Implicit::IS_SIZED;
+    F::Relaxed::IS_SIZED;
+}
+"#,
+        expect![[r#"
+            142..145 'Yes': Yes
+            250..333 '{     ...ZED; }': ()
+            256..277 'F::Exp..._SIZED': Yes
+            283..304 'F::Imp..._SIZED': Yes
+            310..330 'F::Rel..._SIZED': {unknown}
+        "#]],
+    );
+}