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