1 use clippy_utils::diagnostics::span_lint_and_then;
2 use clippy_utils::source::snippet_with_applicability;
3 use clippy_utils::ty::{is_type_diagnostic_item, walk_ptrs_ty_depth};
4 use clippy_utils::{match_def_path, paths};
5 use if_chain::if_chain;
6 use rustc_errors::Applicability;
8 use rustc_lint::LateContext;
9 use rustc_middle::ty::{self, Ty};
10 use rustc_span::symbol::{sym, Symbol};
12 use super::INEFFICIENT_TO_STRING;
14 /// Checks for the `INEFFICIENT_TO_STRING` lint
15 pub fn check<'tcx>(cx: &LateContext<'tcx>, expr: &hir::Expr<'_>, method_name: Symbol, args: &[hir::Expr<'_>]) {
17 if args.len() == 1 && method_name == sym!(to_string);
18 if let Some(to_string_meth_did) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
19 if match_def_path(cx, to_string_meth_did, &paths::TO_STRING_METHOD);
20 if let Some(substs) = cx.typeck_results().node_substs_opt(expr.hir_id);
21 let arg_ty = cx.typeck_results().expr_ty_adjusted(&args[0]);
22 let self_ty = substs.type_at(0);
23 let (deref_self_ty, deref_count) = walk_ptrs_ty_depth(self_ty);
25 if specializes_tostring(cx, deref_self_ty);
29 INEFFICIENT_TO_STRING,
31 &format!("calling `to_string` on `{}`", arg_ty),
34 "`{}` implements `ToString` through a slower blanket impl, but `{}` has a fast specialization of `ToString`",
35 self_ty, deref_self_ty
37 let mut applicability = Applicability::MachineApplicable;
38 let arg_snippet = snippet_with_applicability(cx, args[0].span, "..", &mut applicability);
41 "try dereferencing the receiver",
42 format!("({}{}).to_string()", "*".repeat(deref_count), arg_snippet),
51 /// Returns whether `ty` specializes `ToString`.
52 /// Currently, these are `str`, `String`, and `Cow<'_, str>`.
53 fn specializes_tostring(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
54 if let ty::Str = ty.kind() {
58 if is_type_diagnostic_item(cx, ty, sym::String) {
62 if let ty::Adt(adt, substs) = ty.kind() {
63 match_def_path(cx, adt.did(), &paths::COW) && substs.type_at(1).is_str()