diff options
Diffstat (limited to 'src/tools/clippy/clippy_lints/src/derivable_impls.rs')
-rw-r--r-- | src/tools/clippy/clippy_lints/src/derivable_impls.rs | 117 |
1 files changed, 117 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/derivable_impls.rs b/src/tools/clippy/clippy_lints/src/derivable_impls.rs new file mode 100644 index 000000000..4d7f4076d --- /dev/null +++ b/src/tools/clippy/clippy_lints/src/derivable_impls.rs @@ -0,0 +1,117 @@ +use clippy_utils::diagnostics::span_lint_and_help; +use clippy_utils::{is_default_equivalent, peel_blocks}; +use rustc_hir::{ + def::{DefKind, Res}, + Body, Expr, ExprKind, GenericArg, Impl, ImplItemKind, Item, ItemKind, Node, PathSegment, QPath, TyKind, +}; +use rustc_lint::{LateContext, LateLintPass}; +use rustc_session::{declare_lint_pass, declare_tool_lint}; +use rustc_span::sym; + +declare_clippy_lint! { + /// ### What it does + /// Detects manual `std::default::Default` implementations that are identical to a derived implementation. + /// + /// ### Why is this bad? + /// It is less concise. + /// + /// ### Example + /// ```rust + /// struct Foo { + /// bar: bool + /// } + /// + /// impl Default for Foo { + /// fn default() -> Self { + /// Self { + /// bar: false + /// } + /// } + /// } + /// ``` + /// + /// Use instead: + /// ```rust + /// #[derive(Default)] + /// struct Foo { + /// bar: bool + /// } + /// ``` + /// + /// ### Known problems + /// Derive macros [sometimes use incorrect bounds](https://github.com/rust-lang/rust/issues/26925) + /// in generic types and the user defined `impl` maybe is more generalized or + /// specialized than what derive will produce. This lint can't detect the manual `impl` + /// has exactly equal bounds, and therefore this lint is disabled for types with + /// generic parameters. + #[clippy::version = "1.57.0"] + pub DERIVABLE_IMPLS, + complexity, + "manual implementation of the `Default` trait which is equal to a derive" +} + +declare_lint_pass!(DerivableImpls => [DERIVABLE_IMPLS]); + +fn is_path_self(e: &Expr<'_>) -> bool { + if let ExprKind::Path(QPath::Resolved(_, p)) = e.kind { + matches!(p.res, Res::SelfCtor(..) | Res::Def(DefKind::Ctor(..), _)) + } else { + false + } +} + +impl<'tcx> LateLintPass<'tcx> for DerivableImpls { + fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) { + if_chain! { + if let ItemKind::Impl(Impl { + of_trait: Some(ref trait_ref), + items: [child], + self_ty, + .. + }) = item.kind; + if !cx.tcx.has_attr(item.def_id.to_def_id(), sym::automatically_derived); + if !item.span.from_expansion(); + if let Some(def_id) = trait_ref.trait_def_id(); + if cx.tcx.is_diagnostic_item(sym::Default, def_id); + if let impl_item_hir = child.id.hir_id(); + if let Some(Node::ImplItem(impl_item)) = cx.tcx.hir().find(impl_item_hir); + if let ImplItemKind::Fn(_, b) = &impl_item.kind; + if let Body { value: func_expr, .. } = cx.tcx.hir().body(*b); + if let Some(adt_def) = cx.tcx.type_of(item.def_id).ty_adt_def(); + if let attrs = cx.tcx.hir().attrs(item.hir_id()); + if !attrs.iter().any(|attr| attr.doc_str().is_some()); + if let child_attrs = cx.tcx.hir().attrs(impl_item_hir); + if !child_attrs.iter().any(|attr| attr.doc_str().is_some()); + if adt_def.is_struct(); + then { + if let TyKind::Path(QPath::Resolved(_, p)) = self_ty.kind { + if let Some(PathSegment { args: Some(a), .. }) = p.segments.last() { + for arg in a.args { + if !matches!(arg, GenericArg::Lifetime(_)) { + return; + } + } + } + } + let should_emit = match peel_blocks(func_expr).kind { + ExprKind::Tup(fields) => fields.iter().all(|e| is_default_equivalent(cx, e)), + ExprKind::Call(callee, args) + if is_path_self(callee) => args.iter().all(|e| is_default_equivalent(cx, e)), + ExprKind::Struct(_, fields, _) => fields.iter().all(|ef| is_default_equivalent(cx, ef.expr)), + _ => false, + }; + if should_emit { + let path_string = cx.tcx.def_path_str(adt_def.did()); + span_lint_and_help( + cx, + DERIVABLE_IMPLS, + item.span, + "this `impl` can be derived", + None, + &format!("try annotating `{}` with `#[derive(Default)]`", path_string), + ); + } + } + } + } +} |