Merge rust-lang#10202

10202: fix: Type param hover shows correct sized bounds. r=flodiebold a=iDawer

Closes  rust-lang#9949

This adds implicit `: Sized` bound to type parameters at lowering step.

Hovering on type parameter does not show it's `: Sized` bound be it set explicitly or implicitly. This is because it doesn't track that the bound was set implicitly.

### Perf

```rust
./target/rust-analyzer-baseline-3dae94bf -q analysis-stats --memory-usage .
Database loaded:     4.51s, 311minstr, 110mb (metadata 1.08s, 22minstr, 743kb; build 3.20s, 8730kinstr, -237kb)
  crates: 38, mods: 770, decls: 17173, fns: 12835
Item Collection:     29.63s, 85ginstr, 372mb
  exprs: 353460, ??ty: 364 (0%), ?ty: 232 (0%), !ty: 144
Inference:           118.25s, 284ginstr, 601mb
Total:               147.88s, 370ginstr, 973mb

./target/rust-analyzer-hover-ty-param-dfb15292 -q analysis-stats --memory-usage .
Database loaded:     4.53s, 311minstr, 110mb (metadata 1.10s, 22minstr, 743kb; build 3.20s, 8672kinstr, -189kb)
  crates: 38, mods: 770, decls: 17173, fns: 12835
Item Collection:     29.59s, 85ginstr, 372mb
  exprs: 353460, ??ty: 364 (0%), ?ty: 232 (0%), !ty: 144
Inference:           121.69s, 296ginstr, 601mb
Total:               151.28s, 382ginstr, 974mb

```

Co-authored-by: Dawer <[email protected]>

Author: bors[bot]

crates/hir/src/display.rs

@@ -5,16 +5,19 @@ use hir_def::{
     type_ref::{TypeBound, TypeRef},
     AdtId, GenericDefId,
 };
-use hir_ty::display::{
-    write_bounds_like_dyn_trait_with_prefix, write_visibility, HirDisplay, HirDisplayError,
-    HirFormatter, SizedByDefault,
+use hir_ty::{
+    display::{
+        write_bounds_like_dyn_trait_with_prefix, write_visibility, HirDisplay, HirDisplayError,
+        HirFormatter, SizedByDefault,
+    },
+    Interner, TraitRefExt, WhereClause,
 };
-use hir_ty::Interner;
 use syntax::ast::{self, NameOwner};
 
 use crate::{
-    Adt, Const, ConstParam, Enum, Field, Function, GenericParam, HasVisibility, LifetimeParam,
-    Module, Static, Struct, Trait, TyBuilder, Type, TypeAlias, TypeParam, Union, Variant,
+    Adt, Const, ConstParam, Enum, Field, Function, GenericParam, HasCrate, HasVisibility,
+    LifetimeParam, Module, Static, Struct, Trait, TyBuilder, Type, TypeAlias, TypeParam, Union,
+    Variant,
 };
 
 impl HirDisplay for Function {
@@ -234,12 +237,24 @@ impl HirDisplay for GenericParam {
 impl HirDisplay for TypeParam {
     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
         write!(f, "{}", self.name(f.db))?;
+        if f.omit_verbose_types() {
+            return Ok(());
+        }
+
         let bounds = f.db.generic_predicates_for_param(self.id);
         let substs = TyBuilder::type_params_subst(f.db, self.id.parent);
-        let predicates =
-            bounds.iter().cloned().map(|b| b.substitute(&Interner, &substs)).collect::<Vec<_>>();
-        if !(predicates.is_empty() || f.omit_verbose_types()) {
-            let default_sized = SizedByDefault::Sized { anchor: self.module(f.db).krate().id };
+        let predicates: Vec<_> =
+            bounds.iter().cloned().map(|b| b.substitute(&Interner, &substs)).collect();
+        let krate = self.id.parent.krate(f.db).id;
+        let sized_trait =
+            f.db.lang_item(krate, "sized".into()).and_then(|lang_item| lang_item.as_trait());
+        let has_only_sized_bound = predicates.iter().all(move |pred| match pred.skip_binders() {
+            WhereClause::Implemented(it) => Some(it.hir_trait_id()) == sized_trait,
+            _ => false,
+        });
+        let has_only_not_sized_bound = predicates.is_empty();
+        if !has_only_sized_bound || has_only_not_sized_bound {
+            let default_sized = SizedByDefault::Sized { anchor: krate };
             write_bounds_like_dyn_trait_with_prefix(":", &predicates, default_sized, f)?;
         }
         Ok(())

crates/hir_ty/src/lower.rs

@@ -1024,7 +1024,7 @@ 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);
-    resolver
+    let mut predicates: Vec<_> = resolver
         .where_predicates_in_scope()
         // we have to filter out all other predicates *first*, before attempting to lower them
         .filter(|pred| match pred {
@@ -1038,7 +1038,15 @@ pub(crate) fn generic_predicates_for_param_query(
             WherePredicate::Lifetime { .. } => false,
         })
         .flat_map(|pred| ctx.lower_where_predicate(pred, true).map(|p| make_binders(&generics, p)))
-        .collect()
+        .collect();
+
+    let subst = generics.bound_vars_subst(DebruijnIndex::INNERMOST);
+    let explicitly_unsized_tys = ctx.unsized_types.into_inner();
+    let implicitly_sized_predicates =
+        implicitly_sized_clauses(db, param_id.parent, &explicitly_unsized_tys, &subst, &resolver)
+            .map(|p| make_binders(&generics, crate::wrap_empty_binders(p)));
+    predicates.extend(implicitly_sized_predicates);
+    predicates.into()
 }
 
 pub(crate) fn generic_predicates_for_param_recover(

crates/ide/src/hover.rs

@@ -3564,20 +3564,21 @@ fn foo() {
             r#"
 //- minicore: sized
 struct Foo<T>(T);
-trait Copy {}
-trait Clone {}
-impl<T: Copy + Clone> Foo<T$0> where T: Sized {}
+trait TraitA {}
+trait TraitB {}
+impl<T: TraitA + TraitB> Foo<T$0> where T: Sized {}
 "#,
             expect![[r#"
                 *T*
 
                 ```rust
-                T: Copy + Clone
+                T: TraitA + TraitB
                 ```
             "#]],
         );
         check(
             r#"
+//- minicore: sized
 struct Foo<T>(T);
 impl<T> Foo<T$0> {}
 "#,
@@ -3592,6 +3593,7 @@ impl<T> Foo<T$0> {}
         // lifetimes bounds arent being tracked yet
         check(
             r#"
+//- minicore: sized
 struct Foo<T>(T);
 impl<T: 'static> Foo<T$0> {}
 "#,
@@ -3606,25 +3608,180 @@ impl<T: 'static> Foo<T$0> {}
     }
 
     #[test]
-    fn hover_type_param_not_sized() {
+    fn hover_type_param_sized_bounds() {
+        // implicit `: Sized` bound
         check(
             r#"
 //- minicore: sized
+trait Trait {}
 struct Foo<T>(T);
-trait Copy {}
-trait Clone {}
-impl<T: Copy + Clone> Foo<T$0> where T: ?Sized {}
+impl<T: Trait> Foo<T$0> {}
+"#,
+            expect![[r#"
+                *T*
+
+                ```rust
+                T: Trait
+                ```
+            "#]],
+        );
+        check(
+            r#"
+//- minicore: sized
+trait Trait {}
+struct Foo<T>(T);
+impl<T: Trait + ?Sized> Foo<T$0> {}
 "#,
             expect![[r#"
                 *T*
 
                 ```rust
-                T: Copy + Clone + ?Sized
+                T: Trait + ?Sized
                 ```
             "#]],
         );
     }
 
+    mod type_param_sized_bounds {
+        use super::*;
+
+        #[test]
+        fn single_implicit() {
+            check(
+                r#"
+//- minicore: sized
+fn foo<T$0>() {}
+"#,
+                expect![[r#"
+                    *T*
+
+                    ```rust
+                    T
+                    ```
+                "#]],
+            );
+        }
+
+        #[test]
+        fn single_explicit() {
+            check(
+                r#"
+//- minicore: sized
+fn foo<T$0: Sized>() {}
+"#,
+                expect![[r#"
+                    *T*
+
+                    ```rust
+                    T
+                    ```
+                "#]],
+            );
+        }
+
+        #[test]
+        fn single_relaxed() {
+            check(
+                r#"
+//- minicore: sized
+fn foo<T$0: ?Sized>() {}
+"#,
+                expect![[r#"
+                    *T*
+
+                    ```rust
+                    T: ?Sized
+                    ```
+                "#]],
+            );
+        }
+
+        #[test]
+        fn multiple_implicit() {
+            check(
+                r#"
+//- minicore: sized
+trait Trait {}
+fn foo<T$0: Trait>() {}
+"#,
+                expect![[r#"
+                    *T*
+
+                    ```rust
+                    T: Trait
+                    ```
+                "#]],
+            );
+        }
+
+        #[test]
+        fn multiple_explicit() {
+            check(
+                r#"
+//- minicore: sized
+trait Trait {}
+fn foo<T$0: Trait + Sized>() {}
+"#,
+                expect![[r#"
+                    *T*
+
+                    ```rust
+                    T: Trait
+                    ```
+                "#]],
+            );
+        }
+
+        #[test]
+        fn multiple_relaxed() {
+            check(
+                r#"
+//- minicore: sized
+trait Trait {}
+fn foo<T$0: Trait + ?Sized>() {}
+"#,
+                expect![[r#"
+                    *T*
+
+                    ```rust
+                    T: Trait + ?Sized
+                    ```
+                "#]],
+            );
+        }
+
+        #[test]
+        fn mixed() {
+            check(
+                r#"
+//- minicore: sized
+fn foo<T$0: ?Sized + Sized + Sized>() {}
+"#,
+                expect![[r#"
+                    *T*
+
+                    ```rust
+                    T
+                    ```
+                "#]],
+            );
+            check(
+                r#"
+//- minicore: sized
+trait Trait {}
+fn foo<T$0: Sized + ?Sized + Sized + Trait>() {}
+"#,
+                expect![[r#"
+                    *T*
+
+                    ```rust
+                    T: Trait
+                    ```
+                "#]],
+            );
+        }
+    }
+
     #[test]
     fn hover_const_param() {
         check(