1 use clippy_utils::diagnostics::span_lint_and_help;
2 use clippy_utils::{is_automatically_derived, is_default_equivalent, remove_blocks};
5 Body, Expr, ExprKind, GenericArg, Impl, ImplItemKind, Item, ItemKind, Node, PathSegment, QPath, TyKind,
7 use rustc_lint::{LateContext, LateLintPass};
8 use rustc_session::{declare_lint_pass, declare_tool_lint};
11 declare_clippy_lint! {
13 /// Detects manual `std::default::Default` implementations that are identical to a derived implementation.
15 /// ### Why is this bad?
16 /// It is less concise.
24 /// impl std::default::Default for Foo {
25 /// fn default() -> Self {
33 /// Could be written as:
36 /// #[derive(Default)]
42 /// ### Known problems
43 /// Derive macros [sometimes use incorrect bounds](https://github.com/rust-lang/rust/issues/26925)
44 /// in generic types and the user defined `impl` maybe is more generalized or
45 /// specialized than what derive will produce. This lint can't detect the manual `impl`
46 /// has exactly equal bounds, and therefore this lint is disabled for types with
47 /// generic parameters.
49 #[clippy::version = "1.57.0"]
52 "manual implementation of the `Default` trait which is equal to a derive"
55 declare_lint_pass!(DerivableImpls => [DERIVABLE_IMPLS]);
57 fn is_path_self(e: &Expr<'_>) -> bool {
58 if let ExprKind::Path(QPath::Resolved(_, p)) = e.kind {
59 matches!(p.res, Res::SelfCtor(..) | Res::Def(DefKind::Ctor(..), _))
65 impl<'tcx> LateLintPass<'tcx> for DerivableImpls {
66 fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
68 if let ItemKind::Impl(Impl {
69 of_trait: Some(ref trait_ref),
74 if let attrs = cx.tcx.hir().attrs(item.hir_id());
75 if !is_automatically_derived(attrs);
76 if !item.span.from_expansion();
77 if let Some(def_id) = trait_ref.trait_def_id();
78 if cx.tcx.is_diagnostic_item(sym::Default, def_id);
79 if let impl_item_hir = child.id.hir_id();
80 if let Some(Node::ImplItem(impl_item)) = cx.tcx.hir().find(impl_item_hir);
81 if let ImplItemKind::Fn(_, b) = &impl_item.kind;
82 if let Body { value: func_expr, .. } = cx.tcx.hir().body(*b);
83 if let Some(adt_def) = cx.tcx.type_of(item.def_id).ty_adt_def();
84 if !attrs.iter().any(|attr| attr.doc_str().is_some());
85 if let child_attrs = cx.tcx.hir().attrs(impl_item_hir);
86 if !child_attrs.iter().any(|attr| attr.doc_str().is_some());
87 if adt_def.is_struct();
89 if let TyKind::Path(QPath::Resolved(_, p)) = self_ty.kind {
90 if let Some(PathSegment { args: Some(a), .. }) = p.segments.last() {
92 if !matches!(arg, GenericArg::Lifetime(_)) {
98 let should_emit = match remove_blocks(func_expr).kind {
99 ExprKind::Tup(fields) => fields.iter().all(|e| is_default_equivalent(cx, e)),
100 ExprKind::Call(callee, args)
101 if is_path_self(callee) => args.iter().all(|e| is_default_equivalent(cx, e)),
102 ExprKind::Struct(_, fields, _) => fields.iter().all(|ef| is_default_equivalent(cx, ef.expr)),
106 let path_string = cx.tcx.def_path_str(adt_def.did);
111 "this `impl` can be derived",
113 &format!("try annotating `{}` with `#[derive(Default)]`", path_string),