86 lines
2.9 KiB
Rust
86 lines
2.9 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_sugg;
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use clippy_utils::is_ty_alias;
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use hir::def::Res;
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use hir::ExprKind;
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use rustc_errors::Applicability;
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use rustc_hir as hir;
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::ty;
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use rustc_session::declare_lint_pass;
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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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/// Checks for construction on unit struct using `default`.
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///
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/// ### Why is this bad?
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/// This adds code complexity and an unnecessary function call.
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///
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/// ### Example
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/// ```no_run
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/// # use std::marker::PhantomData;
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/// #[derive(Default)]
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/// struct S<T> {
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/// _marker: PhantomData<T>
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/// }
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///
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/// let _: S<i32> = S {
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/// _marker: PhantomData::default()
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/// };
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/// ```
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/// Use instead:
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/// ```no_run
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/// # use std::marker::PhantomData;
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/// struct S<T> {
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/// _marker: PhantomData<T>
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/// }
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///
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/// let _: S<i32> = S {
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/// _marker: PhantomData
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/// };
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/// ```
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#[clippy::version = "1.71.0"]
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pub DEFAULT_CONSTRUCTED_UNIT_STRUCTS,
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complexity,
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"unit structs can be constructed without calling `default`"
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}
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declare_lint_pass!(DefaultConstructedUnitStructs => [DEFAULT_CONSTRUCTED_UNIT_STRUCTS]);
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fn is_alias(ty: hir::Ty<'_>) -> bool {
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if let hir::TyKind::Path(ref qpath) = ty.kind {
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is_ty_alias(qpath)
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} else {
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false
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}
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}
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impl LateLintPass<'_> for DefaultConstructedUnitStructs {
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fn check_expr<'tcx>(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
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if let hir::ExprKind::Call(fn_expr, &[]) = expr.kind
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// make sure we have a call to `Default::default`
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&& let ExprKind::Path(ref qpath @ hir::QPath::TypeRelative(base, _)) = fn_expr.kind
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// make sure this isn't a type alias:
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// `<Foo as Bar>::Assoc` cannot be used as a constructor
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&& !is_alias(*base)
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&& let Res::Def(_, def_id) = cx.qpath_res(qpath, fn_expr.hir_id)
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&& cx.tcx.is_diagnostic_item(sym::default_fn, def_id)
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// make sure we have a struct with no fields (unit struct)
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&& let ty::Adt(def, ..) = cx.typeck_results().expr_ty(expr).kind()
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&& def.is_struct()
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&& let var @ ty::VariantDef { ctor: Some((hir::def::CtorKind::Const, _)), .. } = def.non_enum_variant()
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&& !var.is_field_list_non_exhaustive()
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&& !expr.span.from_expansion() && !qpath.span().from_expansion()
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{
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span_lint_and_sugg(
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cx,
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DEFAULT_CONSTRUCTED_UNIT_STRUCTS,
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expr.span.with_lo(qpath.qself_span().hi()),
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"use of `default` to create a unit struct",
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"remove this call to `default`",
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String::new(),
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Applicability::MachineApplicable,
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);
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};
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}
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}
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