Merge #1818

1818: Infer box expression r=matklad a=uHOOCCOOHu

Infer `box e` to be `std::boxed::Box<T>` where `e: T`

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

1 files changed, 26 insertions, 0 deletions

diff --git a/crates/ra_hir/src/ty/infer.rs b/crates/ra_hir/src/ty/infer.rs
index 9244ff3cb..1057bbbec 100644
--- a/crates/ra_hir/src/ty/infer.rs
+++ b/crates/ra_hir/src/ty/infer.rs
@@ -1259,6 +1259,14 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 let inner_ty = self.infer_expr(*expr, &expectation);
                 Ty::apply_one(TypeCtor::Ref(*mutability), inner_ty)
             }
+            Expr::Box { expr } => {
+                let inner_ty = self.infer_expr(*expr, &Expectation::none());
+                if let Some(box_) = self.resolve_boxed_box() {
+                    Ty::apply_one(TypeCtor::Adt(box_), inner_ty)
+                } else {
+                    Ty::Unknown
+                }
+            }
             Expr::UnaryOp { expr, op } => {
                 let inner_ty = self.infer_expr(*expr, &Expectation::none());
                 match op {
@@ -1499,6 +1507,24 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             _ => None,
         }
     }
+
+    fn resolve_boxed_box(&self) -> Option<AdtDef> {
+        let boxed_box_path = Path {
+            kind: PathKind::Abs,
+            segments: vec![
+                PathSegment { name: name::STD, args_and_bindings: None },
+                PathSegment { name: name::BOXED_MOD, args_and_bindings: None },
+                PathSegment { name: name::BOX_TYPE, args_and_bindings: None },
+            ],
+        };
+
+        match self.resolver.resolve_path_segments(self.db, &boxed_box_path).into_fully_resolved() {
+            PerNs { types: Some(Def(ModuleDef::Struct(struct_))), .. } => {
+                Some(AdtDef::Struct(struct_))
+            }
+            _ => None,
+        }
+    }
 }
 
 /// The ID of a type variable.