add box expection hint

crates/hir-ty/src/infer/expr.rs

@@ -558,7 +558,7 @@ impl<'a> InferenceContext<'a> {
                 }
                 .intern(Interner)
             }
-            &Expr::Box { expr } => self.infer_expr_box(expr),
+            &Expr::Box { expr } => self.infer_expr_box(expr, expected),
             Expr::UnaryOp { expr, op } => {
                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
                 let inner_ty = self.resolve_ty_shallow(&inner_ty);
@@ -786,10 +786,23 @@ impl<'a> InferenceContext<'a> {
         ty
     }
 
-    fn infer_expr_box(&mut self, inner_expr: ExprId) -> chalk_ir::Ty<Interner> {
+    fn infer_expr_box(&mut self, inner_expr: ExprId, expected: &Expectation) -> Ty {
-        let inner_ty = self.infer_expr_inner(inner_expr, &Expectation::none());
+        if let Some(box_id) = self.resolve_boxed_box() {
-        if let Some(box_) = self.resolve_boxed_box() {
+            let table = &mut self.table;
-            TyBuilder::adt(self.db, box_)
+            let inner_exp = expected
+                .to_option(table)
+                .as_ref()
+                .map(|e| e.as_adt())
+                .flatten()
+                .filter(|(e_adt, _)| e_adt == &box_id)
+                .map(|(_, subts)| {
+                    let g = subts.at(Interner, 0);
+                    Expectation::rvalue_hint(table, Ty::clone(g.assert_ty_ref(Interner)))
+                })
+                .unwrap_or_else(Expectation::none);
+
+            let inner_ty = self.infer_expr_inner(inner_expr, &inner_exp);
+            TyBuilder::adt(self.db, box_id)
                 .push(inner_ty)
                 .fill_with_defaults(self.db, || self.table.new_type_var())
                 .build()

crates/hir-ty/src/tests/simple.rs

@@ -2539,19 +2539,31 @@ impl<T> [T] {
 
 fn test() {
     let vec = <[_]>::into_vec(box [1i32]);
+    let v: Vec<Box<dyn B>> = <[_]> :: into_vec(box [box Astruct]);
 }
+
+trait B{}
+struct Astruct;
+impl B for Astruct {}
 "#,
         expect![[r#"
             569..573 'self': Box<[T], A>
             602..634 '{     ...     }': Vec<T, A>
             612..628 'unimpl...ted!()': Vec<T, A>
-            648..694 '{     ...2]); }': ()
+            648..761 '{     ...t]); }': ()
             658..661 'vec': Vec<i32, Global>
             664..679 '<[_]>::into_vec': fn into_vec<i32, Global>(Box<[i32], Global>) -> Vec<i32, Global>
             664..691 '<[_]>:...1i32])': Vec<i32, Global>
             680..690 'box [1i32]': Box<[i32; 1], Global>
             684..690 '[1i32]': [i32; 1]
             685..689 '1i32': i32
+            701..702 'v': Vec<Box<dyn B, Global>, Global>
+            722..739 '<[_]> ...to_vec': fn into_vec<Box<dyn B, Global>, Global>(Box<[Box<dyn B, Global>], Global>) -> Vec<Box<dyn B, Global>, Global>
+            722..758 '<[_]> ...ruct])': Vec<Box<dyn B, Global>, Global>
+            740..757 'box [b...truct]': Box<[Box<dyn B, Global>; 1], Global>
+            744..757 '[box Astruct]': [Box<dyn B, Global>; 1]
+            745..756 'box Astruct': Box<Astruct, Global>
+            749..756 'Astruct': Astruct
         "#]],
     )
 }

crates/hir-ty/src/tests/traits.rs

@@ -2999,15 +2999,15 @@ fn foo() {
             216..217 's': Option<i32>
             220..224 'None': Option<i32>
             234..235 'f': Box<dyn FnOnce(&Option<i32>)>
-            269..282 'box (|ps| {})': Box<|{unknown}| -> ()>
+            269..282 'box (|ps| {})': Box<|&Option<i32>| -> ()>
-            274..281 '|ps| {}': |{unknown}| -> ()
+            274..281 '|ps| {}': |&Option<i32>| -> ()
-            275..277 'ps': {unknown}
+            275..277 'ps': &Option<i32>
             279..281 '{}': ()
             288..289 'f': Box<dyn FnOnce(&Option<i32>)>
             288..293 'f(&s)': ()
             290..292 '&s': &Option<i32>
             291..292 's': Option<i32>
-            269..282: expected Box<dyn FnOnce(&Option<i32>)>, got Box<|{unknown}| -> ()>
+            269..282: expected Box<dyn FnOnce(&Option<i32>)>, got Box<|&Option<i32>| -> ()>
         "#]],
     );
 }