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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::last_path_segment;
use clippy_utils::source::snippet_with_context;
use clippy_utils::{match_def_path, paths};
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::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
/// ```rust
/// let _ = std::iter::Empty::<usize>::default();
/// let iter: std::iter::Empty<usize> = std::iter::Empty::default();
/// ```
/// Use instead:
/// ```rust
/// 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
&& match_def_path(cx, *def_id, &paths::ITER_EMPTY)
&& 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()
}
}
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