1 use clippy_utils::diagnostics::span_lint_and_sugg;
2 use clippy_utils::source::snippet_with_applicability;
3 use clippy_utils::ty::is_type_diagnostic_item;
4 use clippy_utils::{get_parent_expr, is_lang_ctor, match_def_path, paths};
5 use if_chain::if_chain;
6 use rustc_errors::Applicability;
7 use rustc_hir::LangItem::ResultErr;
8 use rustc_hir::{Expr, ExprKind, LangItem, MatchSource, QPath};
9 use rustc_lint::LateContext;
10 use rustc_middle::ty::{self, Ty};
11 use rustc_span::{hygiene, sym};
15 pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, scrutinee: &'tcx Expr<'_>) {
16 // Looks for a structure like this:
17 // match ::std::ops::Try::into_result(Err(5)) {
18 // ::std::result::Result::Err(err) =>
19 // #[allow(unreachable_code)]
20 // return ::std::ops::Try::from_error(::std::convert::From::from(err)),
21 // ::std::result::Result::Ok(val) =>
22 // #[allow(unreachable_code)]
26 if let ExprKind::Call(match_fun, [try_arg, ..]) = scrutinee.kind;
27 if let ExprKind::Path(ref match_fun_path) = match_fun.kind;
28 if matches!(match_fun_path, QPath::LangItem(LangItem::TryTraitBranch, ..));
29 if let ExprKind::Call(err_fun, [err_arg, ..]) = try_arg.kind;
30 if let ExprKind::Path(ref err_fun_path) = err_fun.kind;
31 if is_lang_ctor(cx, err_fun_path, ResultErr);
32 if let Some(return_ty) = find_return_type(cx, &expr.kind);
38 if let Some(ty) = result_error_type(cx, return_ty) {
42 } else if let Some(ty) = poll_result_error_type(cx, return_ty) {
43 prefix = "Poll::Ready(Err(";
46 } else if let Some(ty) = poll_option_result_error_type(cx, return_ty) {
47 prefix = "Poll::Ready(Some(Err(";
54 let expr_err_ty = cx.typeck_results().expr_ty(err_arg);
55 let span = hygiene::walk_chain(err_arg.span, try_arg.span.ctxt());
56 let mut applicability = Applicability::MachineApplicable;
57 let origin_snippet = snippet_with_applicability(cx, span, "_", &mut applicability);
58 let ret_prefix = if get_parent_expr(cx, expr).map_or(false, |e| matches!(e.kind, ExprKind::Ret(_))) {
63 let suggestion = if err_ty == expr_err_ty {
64 format!("{}{}{}{}", ret_prefix, prefix, origin_snippet, suffix)
66 format!("{}{}{}.into(){}", ret_prefix, prefix, origin_snippet, suffix)
73 "returning an `Err(_)` with the `?` operator",
82 /// Finds function return type by examining return expressions in match arms.
83 fn find_return_type<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx ExprKind<'_>) -> Option<Ty<'tcx>> {
84 if let ExprKind::Match(_, arms, MatchSource::TryDesugar) = expr {
85 for arm in arms.iter() {
86 if let ExprKind::Ret(Some(ret)) = arm.body.kind {
87 return Some(cx.typeck_results().expr_ty(ret));
94 /// Extracts the error type from Result<T, E>.
95 fn result_error_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
97 if let ty::Adt(_, subst) = ty.kind();
98 if is_type_diagnostic_item(cx, ty, sym::Result);
100 Some(subst.type_at(1))
107 /// Extracts the error type from Poll<Result<T, E>>.
108 fn poll_result_error_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
110 if let ty::Adt(def, subst) = ty.kind();
111 if match_def_path(cx, def.did(), &paths::POLL);
112 let ready_ty = subst.type_at(0);
114 if let ty::Adt(ready_def, ready_subst) = ready_ty.kind();
115 if cx.tcx.is_diagnostic_item(sym::Result, ready_def.did());
117 Some(ready_subst.type_at(1))
124 /// Extracts the error type from Poll<Option<Result<T, E>>>.
125 fn poll_option_result_error_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
127 if let ty::Adt(def, subst) = ty.kind();
128 if match_def_path(cx, def.did(), &paths::POLL);
129 let ready_ty = subst.type_at(0);
131 if let ty::Adt(ready_def, ready_subst) = ready_ty.kind();
132 if cx.tcx.is_diagnostic_item(sym::Option, ready_def.did());
133 let some_ty = ready_subst.type_at(0);
135 if let ty::Adt(some_def, some_subst) = some_ty.kind();
136 if cx.tcx.is_diagnostic_item(sym::Result, some_def.did());
138 Some(some_subst.type_at(1))