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