Compiler does not suggest to dereference a reference to reference

[ChayimFriedman2]

If I miss a * when assigning to a variable, rustc suggests dereferencing it:

let mut v: &mut ();
v = ();

error[E0308]: mismatched types
 --> src/main.rs:3:9
  |
2 |     let v: &mut ();
  |            ------- expected due to this type
3 |     v = ();
  |         ^^ expected `&mut ()`, found `()`
  |
help: consider dereferencing here to assign to the mutable borrowed piece of memory
  |
3 |     *v = ();
  |     +

Playground.

But not the referent is a reference:

let v: &mut &();
v = &();

error[E0308]: mismatched types
 --> src/main.rs:3:9
  |
3 |     v = &();
  |         ^^^ types differ in mutability
  |
  = note: expected mutable reference `&mut &()`
                     found reference `&()`

Playground.

This is because in compiler/rustc_typeck/src/check/demand.rs, we first check whether both the LHS and RHS are references and try to suggest adding/removing b"...". But even if we did not succeed in that check, we don't continue to the next check where we check whether the LHS is a reference and should be dereferenced:

rust/compiler/rustc_typeck/src/check/demand.rs

Lines 593 to 627 in b117335

	(_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (exp.kind(), check.kind()) {
	(&ty::Str, &ty::Array(arr, _) | &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
	if let hir::ExprKind::Lit(_) = expr.kind {
	if let Ok(src) = sm.span_to_snippet(sp) {
	if replace_prefix(&src, "b\"", "\"").is_some() {
	let pos = sp.lo() + BytePos(1);
	return Some((
	sp.with_hi(pos),
	"consider removing the leading `b`",
	String::new(),
	Applicability::MachineApplicable,
	true,
	));
	}
	}
	}
	}
	(&ty::Array(arr, _) | &ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
	if let hir::ExprKind::Lit(_) = expr.kind {
	if let Ok(src) = sm.span_to_snippet(sp) {
	if replace_prefix(&src, "\"", "b\"").is_some() {
	return Some((
	sp.shrink_to_lo(),
	"consider adding a leading `b`",
	"b".to_string(),
	Applicability::MachineApplicable,
	true,
	));
	}
	}
	}
	}
	_ => {}
	},
	(_, &ty::Ref(_, _, mutability), _) => {

[compiler-errors]

This is fixed.