librustc_typeck: use diag item instead of string compare

Author: da-x

src/librustc_span/symbol.rs

@@ -1043,6 +1043,7 @@ symbols! {
  stop_after_dataflow,
  str,
  str_alloc,
+ string_type,
  stringify,
  struct_field_attributes,
  struct_inherit,

src/librustc_typeck/check/op.rs

@@ -562,7 +562,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  on the left and may require reallocation. This \
  requires ownership of the string on the left";
 
- let is_std_string = |ty| &format!("{:?}", ty) == "std::string::String";
+ let string_type = self.tcx.get_diagnostic_item(sym::string_type);
+ let is_std_string = |ty: Ty<'tcx>| match &ty.ty_adt_def() {
+ Some(ty_def) => Some(ty_def.did) == string_type,
+ None => false,
+ };
 
  match (&lhs_ty.kind, &rhs_ty.kind) {
  (&Ref(_, l_ty, _), &Ref(_, r_ty, _)) // &str or &String + &str, &String or &&str