| use clippy_utils::diagnostics::span_lint_and_sugg; |
| use clippy_utils::last_path_segment; |
| use clippy_utils::source::snippet_with_context; |
| use rustc_errors::Applicability; |
| use rustc_hir::{def, Expr, ExprKind, GenericArg, QPath, TyKind}; |
| use rustc_lint::{LateContext, LateLintPass}; |
| use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| use rustc_span::{sym, SyntaxContext}; |
| |
| declare_clippy_lint! { |
| /// ### What it does |
| /// It checks for `std::iter::Empty::default()` and suggests replacing it with |
| /// `std::iter::empty()`. |
| /// ### Why is this bad? |
| /// `std::iter::empty()` is the more idiomatic way. |
| /// ### Example |
| /// ```no_run |
| /// let _ = std::iter::Empty::<usize>::default(); |
| /// let iter: std::iter::Empty<usize> = std::iter::Empty::default(); |
| /// ``` |
| /// Use instead: |
| /// ```no_run |
| /// let _ = std::iter::empty::<usize>(); |
| /// let iter: std::iter::Empty<usize> = std::iter::empty(); |
| /// ``` |
| #[clippy::version = "1.64.0"] |
| pub DEFAULT_INSTEAD_OF_ITER_EMPTY, |
| style, |
| "check `std::iter::Empty::default()` and replace with `std::iter::empty()`" |
| } |
| declare_lint_pass!(DefaultIterEmpty => [DEFAULT_INSTEAD_OF_ITER_EMPTY]); |
| |
| impl<'tcx> LateLintPass<'tcx> for DefaultIterEmpty { |
| fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { |
| if let ExprKind::Call(iter_expr, []) = &expr.kind |
| && let ExprKind::Path(QPath::TypeRelative(ty, _)) = &iter_expr.kind |
| && let TyKind::Path(ty_path) = &ty.kind |
| && let QPath::Resolved(None, path) = ty_path |
| && let def::Res::Def(_, def_id) = &path.res |
| && cx.tcx.is_diagnostic_item(sym::IterEmpty, *def_id) |
| && let ctxt = expr.span.ctxt() |
| && ty.span.ctxt() == ctxt |
| { |
| let mut applicability = Applicability::MachineApplicable; |
| let sugg = make_sugg(cx, ty_path, ctxt, &mut applicability); |
| span_lint_and_sugg( |
| cx, |
| DEFAULT_INSTEAD_OF_ITER_EMPTY, |
| expr.span, |
| "`std::iter::empty()` is the more idiomatic way", |
| "try", |
| sugg, |
| applicability, |
| ); |
| } |
| } |
| } |
| |
| fn make_sugg( |
| cx: &LateContext<'_>, |
| ty_path: &rustc_hir::QPath<'_>, |
| ctxt: SyntaxContext, |
| applicability: &mut Applicability, |
| ) -> String { |
| if let Some(last) = last_path_segment(ty_path).args |
| && let Some(iter_ty) = last.args.iter().find_map(|arg| match arg { |
| GenericArg::Type(ty) => Some(ty), |
| _ => None, |
| }) |
| { |
| format!( |
| "std::iter::empty::<{}>()", |
| snippet_with_context(cx, iter_ty.span, ctxt, "..", applicability).0 |
| ) |
| } else { |
| "std::iter::empty()".to_owned() |
| } |
| } |