Handle box with allocator

In 1.49.0, the definition of Box was modified to support an optional
Allocator[1]. Adapt the parsing of the `box` keyword to supply the
expected number of parameters to the constructor.

[1] https://github.com/rust-lang/rust/commit/f288cd2e179f600fa00c2a407206a12f6c5a91e0

1 files changed, 4 insertions, 1 deletions

diff --git a/crates/hir_ty/src/infer/expr.rs b/crates/hir_ty/src/infer/expr.rs
index 9bf3b51b0..d7351d212 100644
--- a/crates/hir_ty/src/infer/expr.rs
+++ b/crates/hir_ty/src/infer/expr.rs
@@ -491,7 +491,10 @@ impl<'a> InferenceContext<'a> {
             Expr::Box { expr } => {
                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
                 if let Some(box_) = self.resolve_boxed_box() {
-                    Ty::apply_one(TypeCtor::Adt(box_), inner_ty)
+                    let mut sb = Substs::build_for_type_ctor(self.db, TypeCtor::Adt(box_));
+                    sb = sb.push(inner_ty);
+                    sb = sb.fill(repeat_with(|| self.table.new_type_var()));
+                    Ty::apply(TypeCtor::Adt(box_), sb.build())
                 } else {
                     Ty::Unknown
                 }