Rollup merge of #71524 - ldm0:ptrparam, r=matthewjasper

Minimize parameter of coerce_borrowed_pointer()

Change last parameter of `coerce_borrowed_pointer()` from `TypeAndMut` to `Mutability` (similar to `coerce_unsafe_ptr()`), since the `TypeAndMut::ty` is never used directly in this function.

src/librustc_typeck/check/coercion.rs

@@ -211,12 +211,9 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
             ty::RawPtr(mt_b) => {
                 return self.coerce_unsafe_ptr(a, b, mt_b.mutbl);
             }
-
-            ty::Ref(r_b, ty, mutbl) => {
-                let mt_b = ty::TypeAndMut { ty, mutbl };
-                return self.coerce_borrowed_pointer(a, b, r_b, mt_b);
+            ty::Ref(r_b, _, mutbl_b) => {
+                return self.coerce_borrowed_pointer(a, b, r_b, mutbl_b);
             }
-
             _ => {}
         }
 
@@ -255,7 +252,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
         a: Ty<'tcx>,
         b: Ty<'tcx>,
         r_b: ty::Region<'tcx>,
-        mt_b: TypeAndMut<'tcx>,
+        mutbl_b: hir::Mutability,
     ) -> CoerceResult<'tcx> {
         debug!("coerce_borrowed_pointer(a={:?}, b={:?})", a, b);
 
@@ -268,7 +265,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
         let (r_a, mt_a) = match a.kind {
             ty::Ref(r_a, ty, mutbl) => {
                 let mt_a = ty::TypeAndMut { ty, mutbl };
-                coerce_mutbls(mt_a.mutbl, mt_b.mutbl)?;
+                coerce_mutbls(mt_a.mutbl, mutbl_b)?;
                 (r_a, mt_a)
             }
             _ => return self.unify_and(a, b, identity),
@@ -364,7 +361,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
                 r_a // [3] above
             } else {
                 if r_borrow_var.is_none() {
-                    // create var lazilly, at most once
+                    // create var lazily, at most once
                     let coercion = Coercion(span);
                     let r = self.next_region_var(coercion);
                     r_borrow_var = Some(r); // [4] above
@@ -375,7 +372,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
                 r,
                 TypeAndMut {
                     ty: referent_ty,
-                    mutbl: mt_b.mutbl, // [1] above
+                    mutbl: mutbl_b, // [1] above
                 },
             );
             match self.unify(derefd_ty_a, b) {
@@ -417,11 +414,11 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
             // `self.x` both have `&mut `type would be a move of
             // `self.x`, but we auto-coerce it to `foo(&mut *self.x)`,
             // which is a borrow.
-            assert_eq!(mt_b.mutbl, hir::Mutability::Not); // can only coerce &T -> &U
+            assert_eq!(mutbl_b, hir::Mutability::Not); // can only coerce &T -> &U
             return success(vec![], ty, obligations);
         }
 
-        let needs = Needs::maybe_mut_place(mt_b.mutbl);
+        let needs = Needs::maybe_mut_place(mutbl_b);
         let InferOk { value: mut adjustments, obligations: o } =
             autoderef.adjust_steps_as_infer_ok(self, needs);
         obligations.extend(o);
@@ -433,7 +430,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
             ty::Ref(r_borrow, _, _) => r_borrow,
             _ => span_bug!(span, "expected a ref type, got {:?}", ty),
         };
-        let mutbl = match mt_b.mutbl {
+        let mutbl = match mutbl_b {
             hir::Mutability::Not => AutoBorrowMutability::Not,
             hir::Mutability::Mut => {
                 AutoBorrowMutability::Mut { allow_two_phase_borrow: self.allow_two_phase }