1 use clippy_utils::diagnostics::span_lint_and_help;
2 use clippy_utils::ty::{implements_trait, is_type_diagnostic_item};
3 use clippy_utils::{get_trait_def_id, paths, return_ty, trait_ref_of_method};
4 use if_chain::if_chain;
5 use rustc_hir::{ImplItem, ImplItemKind};
6 use rustc_lint::{LateContext, LateLintPass};
7 use rustc_session::{declare_lint_pass, declare_tool_lint};
10 declare_clippy_lint! {
11 /// **What it does:** Checks for the definition of inherent methods with a signature of `to_string(&self) -> String`.
13 /// **Why is this bad?** This method is also implicitly defined if a type implements the `Display` trait. As the functionality of `Display` is much more versatile, it should be preferred.
15 /// **Known problems:** None
24 /// pub fn to_string(&self) -> String {
25 /// "I am A".to_string()
36 /// impl fmt::Display for A {
37 /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
38 /// write!(f, "I am A")
42 pub INHERENT_TO_STRING,
44 "type implements inherent method `to_string()`, but should instead implement the `Display` trait"
47 declare_clippy_lint! {
48 /// **What it does:** Checks for the definition of inherent methods with a signature of `to_string(&self) -> String` and if the type implementing this method also implements the `Display` trait.
50 /// **Why is this bad?** This method is also implicitly defined if a type implements the `Display` trait. The less versatile inherent method will then shadow the implementation introduced by `Display`.
52 /// **Known problems:** None
63 /// pub fn to_string(&self) -> String {
64 /// "I am A".to_string()
68 /// impl fmt::Display for A {
69 /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
70 /// write!(f, "I am A, too")
81 /// impl fmt::Display for A {
82 /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
83 /// write!(f, "I am A")
87 pub INHERENT_TO_STRING_SHADOW_DISPLAY,
89 "type implements inherent method `to_string()`, which gets shadowed by the implementation of the `Display` trait"
92 declare_lint_pass!(InherentToString => [INHERENT_TO_STRING, INHERENT_TO_STRING_SHADOW_DISPLAY]);
94 impl<'tcx> LateLintPass<'tcx> for InherentToString {
95 fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &'tcx ImplItem<'_>) {
96 if impl_item.span.from_expansion() {
101 // Check if item is a method, called to_string and has a parameter 'self'
102 if let ImplItemKind::Fn(ref signature, _) = impl_item.kind;
103 if impl_item.ident.name.as_str() == "to_string";
104 let decl = &signature.decl;
105 if decl.implicit_self.has_implicit_self();
106 if decl.inputs.len() == 1;
107 if impl_item.generics.params.is_empty();
109 // Check if return type is String
110 if is_type_diagnostic_item(cx, return_ty(cx, impl_item.hir_id()), sym::string_type);
112 // Filters instances of to_string which are required by a trait
113 if trait_ref_of_method(cx, impl_item.hir_id()).is_none();
116 show_lint(cx, impl_item);
122 fn show_lint(cx: &LateContext<'_>, item: &ImplItem<'_>) {
123 let display_trait_id = get_trait_def_id(cx, &paths::DISPLAY_TRAIT).expect("Failed to get trait ID of `Display`!");
125 // Get the real type of 'self'
126 let self_type = cx.tcx.fn_sig(item.def_id).input(0);
127 let self_type = self_type.skip_binder().peel_refs();
129 // Emit either a warning or an error
130 if implements_trait(cx, self_type, display_trait_id, &[]) {
133 INHERENT_TO_STRING_SHADOW_DISPLAY,
136 "type `{}` implements inherent method `to_string(&self) -> String` which shadows the implementation of `Display`",
137 self_type.to_string()
140 &format!("remove the inherent method from type `{}`", self_type.to_string()),
148 "implementation of inherent method `to_string(&self) -> String` for type `{}`",
149 self_type.to_string()
152 &format!("implement trait `Display` for type `{}` instead", self_type.to_string()),