1 use clippy_utils::diagnostics::span_lint_and_help;
2 use clippy_utils::{in_macro, is_automatically_derived, is_default_equivalent, remove_blocks};
5 Body, Expr, ExprKind, Impl, ImplItemKind, Item, ItemKind, Node, QPath,
7 use rustc_lint::{LateContext, LateLintPass};
8 use rustc_middle::ty::TypeFoldable;
9 use rustc_session::{declare_lint_pass, declare_tool_lint};
12 declare_clippy_lint! {
14 /// Detects manual `std::default::Default` implementations that are identical to a derived implementation.
16 /// ### Why is this bad?
17 /// It is less concise.
25 /// impl std::default::Default for Foo {
26 /// fn default() -> Self {
34 /// Could be written as:
37 /// #[derive(Default)]
43 /// ### Known problems
44 /// Derive macros [sometimes use incorrect bounds](https://github.com/rust-lang/rust/issues/26925)
45 /// in generic types and the user defined `impl` maybe is more generalized or
46 /// specialized than what derive will produce. This lint can't detect the manual `impl`
47 /// has exactly equal bounds, and therefore this lint is disabled for types with
48 /// generic parameters.
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),
73 if let attrs = cx.tcx.hir().attrs(item.hir_id());
74 if !is_automatically_derived(attrs);
75 if !in_macro(item.span);
76 if let Some(def_id) = trait_ref.trait_def_id();
77 if cx.tcx.is_diagnostic_item(sym::Default, def_id);
78 if let impl_item_hir = child.id.hir_id();
79 if let Some(Node::ImplItem(impl_item)) = cx.tcx.hir().find(impl_item_hir);
80 if let ImplItemKind::Fn(_, b) = &impl_item.kind;
81 if let Body { value: func_expr, .. } = cx.tcx.hir().body(*b);
82 if let Some(adt_def) = cx.tcx.type_of(item.def_id).ty_adt_def();
84 if cx.tcx.type_of(item.def_id).definitely_has_param_types_or_consts(cx.tcx) {
87 let should_emit = match remove_blocks(func_expr).kind {
88 ExprKind::Tup(fields) => fields.iter().all(|e| is_default_equivalent(cx, e)),
89 ExprKind::Call(callee, args)
90 if is_path_self(callee) => args.iter().all(|e| is_default_equivalent(cx, e)),
91 ExprKind::Struct(_, fields, _) => fields.iter().all(|ef| is_default_equivalent(cx, ef.expr)),
95 let path_string = cx.tcx.def_path_str(adt_def.did);
100 "this `impl` can be derived",
102 &format!("try annotating `{}` with `#[derive(Default)]`", path_string),