67 lines
2.4 KiB
Rust
67 lines
2.4 KiB
Rust
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use clippy_utils::{diagnostics::span_lint_and_sugg, is_from_proc_macro, match_def_path, paths};
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use hir::{def::Res, 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, declare_tool_lint};
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declare_clippy_lint! {
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/// ### What it does
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/// Check 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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/// ```rust
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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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/// ```rust
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/// let _: S<i32> = Something {
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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_STRUCT,
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complexity,
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"unit structs can be contructed without calling `default`"
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}
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declare_lint_pass!(DefaultConstructedUnitStruct => [DEFAULT_CONSTRUCTED_UNIT_STRUCT]);
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impl LateLintPass<'_> for DefaultConstructedUnitStruct {
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fn check_expr<'tcx>(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
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if_chain!(
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// make sure we have a call to `Default::default`
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if let hir::ExprKind::Call(fn_expr, &[]) = expr.kind;
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if let ExprKind::Path(ref qpath) = fn_expr.kind;
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if let Res::Def(_, def_id) = cx.qpath_res(qpath, fn_expr.hir_id);
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if match_def_path(cx, def_id, &paths::DEFAULT_TRAIT_METHOD);
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// make sure we have a struct with no fields (unit struct)
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if let ty::Adt(def, ..) = cx.typeck_results().expr_ty(expr).kind();
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if def.is_struct() && def.is_payloadfree()
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&& !def.non_enum_variant().is_field_list_non_exhaustive()
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&& !is_from_proc_macro(cx, expr);
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then {
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span_lint_and_sugg(
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cx,
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DEFAULT_CONSTRUCTED_UNIT_STRUCT,
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qpath.last_segment_span(),
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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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}
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