1 use clippy_utils::diagnostics::span_lint_hir_and_then;
2 use clippy_utils::return_ty;
3 use clippy_utils::source::snippet;
4 use clippy_utils::sugg::DiagnosticBuilderExt;
5 use if_chain::if_chain;
6 use rustc_errors::Applicability;
8 use rustc_hir::HirIdSet;
9 use rustc_lint::{LateContext, LateLintPass, LintContext};
10 use rustc_middle::lint::in_external_macro;
11 use rustc_middle::ty::TyS;
12 use rustc_session::{declare_tool_lint, impl_lint_pass};
15 declare_clippy_lint! {
17 /// Checks for types with a `fn new() -> Self` method and no
19 /// [`Default`](https://doc.rust-lang.org/std/default/trait.Default.html).
21 /// ### Why is this bad?
22 /// The user might expect to be able to use
23 /// [`Default`](https://doc.rust-lang.org/std/default/trait.Default.html) as the
24 /// type can be constructed without arguments.
31 /// fn new() -> Self {
37 /// To fix the lint, add a `Default` implementation that delegates to `new`:
42 /// impl Default for Foo {
43 /// fn default() -> Self {
48 #[clippy::version = "pre 1.29.0"]
49 pub NEW_WITHOUT_DEFAULT,
51 "`fn new() -> Self` method without `Default` implementation"
54 #[derive(Clone, Default)]
55 pub struct NewWithoutDefault {
56 impling_types: Option<HirIdSet>,
59 impl_lint_pass!(NewWithoutDefault => [NEW_WITHOUT_DEFAULT]);
61 impl<'tcx> LateLintPass<'tcx> for NewWithoutDefault {
62 #[allow(clippy::too_many_lines)]
63 fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
64 if let hir::ItemKind::Impl(hir::Impl {
67 self_ty: impl_self_ty,
72 for assoc_item in items {
73 if assoc_item.kind == (hir::AssocItemKind::Fn { has_self: false }) {
74 let impl_item = cx.tcx.hir().impl_item(assoc_item.id);
75 if in_external_macro(cx.sess(), impl_item.span) {
78 if let hir::ImplItemKind::Fn(ref sig, _) = impl_item.kind {
79 let name = impl_item.ident.name;
80 let id = impl_item.hir_id();
81 if sig.header.constness == hir::Constness::Const {
82 // can't be implemented by default
85 if sig.header.unsafety == hir::Unsafety::Unsafe {
86 // can't be implemented for unsafe new
93 .any(|gen| matches!(gen.kind, hir::GenericParamKind::Type { .. }))
95 // when the result of `new()` depends on a type parameter we should not require
101 if sig.decl.inputs.is_empty();
103 if cx.access_levels.is_reachable(impl_item.def_id);
104 let self_def_id = cx.tcx.hir().local_def_id(cx.tcx.hir().get_parent_item(id));
105 let self_ty = cx.tcx.type_of(self_def_id);
106 if TyS::same_type(self_ty, return_ty(cx, id));
107 if let Some(default_trait_id) = cx.tcx.get_diagnostic_item(sym::Default);
109 if self.impling_types.is_none() {
110 let mut impls = HirIdSet::default();
111 cx.tcx.for_each_impl(default_trait_id, |d| {
112 if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
113 if let Some(local_def_id) = ty_def.did.as_local() {
114 impls.insert(cx.tcx.hir().local_def_id_to_hir_id(local_def_id));
118 self.impling_types = Some(impls);
121 // Check if a Default implementation exists for the Self type, regardless of
124 if let Some(ref impling_types) = self.impling_types;
125 if let Some(self_def) = cx.tcx.type_of(self_def_id).ty_adt_def();
126 if let Some(self_local_did) = self_def.did.as_local();
127 let self_id = cx.tcx.hir().local_def_id_to_hir_id(self_local_did);
128 if impling_types.contains(&self_id);
134 let generics_sugg = snippet(cx, generics.span, "");
135 let self_ty_fmt = self_ty.to_string();
136 let self_type_snip = snippet(cx, impl_self_ty.span, &self_ty_fmt);
137 span_lint_hir_and_then(
143 "you should consider adding a `Default` implementation for `{}`",
147 diag.suggest_prepend_item(
151 &create_new_without_default_suggest_msg(&self_type_snip, &generics_sugg),
152 Applicability::MaybeIncorrect,
165 fn create_new_without_default_suggest_msg(self_type_snip: &str, generics_sugg: &str) -> String {
168 "impl{} Default for {} {{
169 fn default() -> Self {{
172 }}", generics_sugg, self_type_snip)