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, LateLintPass};
10 use rustc_middle::lint::in_external_macro;
11 use rustc_middle::ty::{self, Ty};
12 use rustc_session::{declare_lint_pass, declare_tool_lint};
13 use rustc_span::{hygiene, sym};
15 declare_clippy_lint! {
17 /// Checks for usages of `Err(x)?`.
19 /// ### Why is this bad?
20 /// The `?` operator is designed to allow calls that
21 /// can fail to be easily chained. For example, `foo()?.bar()` or
22 /// `foo(bar()?)`. Because `Err(x)?` can't be used that way (it will
23 /// always return), it is more clear to write `return Err(x)`.
27 /// fn foo(fail: bool) -> Result<i32, String> {
37 /// fn foo(fail: bool) -> Result<i32, String> {
39 /// return Err("failed".into());
44 #[clippy::version = "1.38.0"]
47 "return errors explicitly rather than hiding them behind a `?`"
50 declare_lint_pass!(TryErr => [TRY_ERR]);
52 impl<'tcx> LateLintPass<'tcx> for TryErr {
53 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
54 // Looks for a structure like this:
55 // match ::std::ops::Try::into_result(Err(5)) {
56 // ::std::result::Result::Err(err) =>
57 // #[allow(unreachable_code)]
58 // return ::std::ops::Try::from_error(::std::convert::From::from(err)),
59 // ::std::result::Result::Ok(val) =>
60 // #[allow(unreachable_code)]
64 if !in_external_macro(cx.tcx.sess, expr.span);
65 if let ExprKind::Match(match_arg, _, MatchSource::TryDesugar) = expr.kind;
66 if let ExprKind::Call(match_fun, try_args) = match_arg.kind;
67 if let ExprKind::Path(ref match_fun_path) = match_fun.kind;
68 if matches!(match_fun_path, QPath::LangItem(LangItem::TryTraitBranch, _));
69 if let Some(try_arg) = try_args.get(0);
70 if let ExprKind::Call(err_fun, err_args) = try_arg.kind;
71 if let Some(err_arg) = err_args.get(0);
72 if let ExprKind::Path(ref err_fun_path) = err_fun.kind;
73 if is_lang_ctor(cx, err_fun_path, ResultErr);
74 if let Some(return_ty) = find_return_type(cx, &expr.kind);
80 if let Some(ty) = result_error_type(cx, return_ty) {
84 } else if let Some(ty) = poll_result_error_type(cx, return_ty) {
85 prefix = "Poll::Ready(Err(";
88 } else if let Some(ty) = poll_option_result_error_type(cx, return_ty) {
89 prefix = "Poll::Ready(Some(Err(";
96 let expr_err_ty = cx.typeck_results().expr_ty(err_arg);
97 let span = hygiene::walk_chain(err_arg.span, try_arg.span.ctxt());
98 let mut applicability = Applicability::MachineApplicable;
99 let origin_snippet = snippet_with_applicability(cx, span, "_", &mut applicability);
100 let ret_prefix = if get_parent_expr(cx, expr).map_or(false, |e| matches!(e.kind, ExprKind::Ret(_))) {
101 "" // already returns
105 let suggestion = if err_ty == expr_err_ty {
106 format!("{}{}{}{}", ret_prefix, prefix, origin_snippet, suffix)
108 format!("{}{}{}.into(){}", ret_prefix, prefix, origin_snippet, suffix)
115 "returning an `Err(_)` with the `?` operator",
125 /// Finds function return type by examining return expressions in match arms.
126 fn find_return_type<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx ExprKind<'_>) -> Option<Ty<'tcx>> {
127 if let ExprKind::Match(_, arms, MatchSource::TryDesugar) = expr {
128 for arm in arms.iter() {
129 if let ExprKind::Ret(Some(ret)) = arm.body.kind {
130 return Some(cx.typeck_results().expr_ty(ret));
137 /// Extracts the error type from Result<T, E>.
138 fn result_error_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
140 if let ty::Adt(_, subst) = ty.kind();
141 if is_type_diagnostic_item(cx, ty, sym::Result);
143 Some(subst.type_at(1))
150 /// Extracts the error type from Poll<Result<T, E>>.
151 fn poll_result_error_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
153 if let ty::Adt(def, subst) = ty.kind();
154 if match_def_path(cx, def.did, &paths::POLL);
155 let ready_ty = subst.type_at(0);
157 if let ty::Adt(ready_def, ready_subst) = ready_ty.kind();
158 if cx.tcx.is_diagnostic_item(sym::Result, ready_def.did);
160 Some(ready_subst.type_at(1))
167 /// Extracts the error type from Poll<Option<Result<T, E>>>.
168 fn poll_option_result_error_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
170 if let ty::Adt(def, subst) = ty.kind();
171 if match_def_path(cx, def.did, &paths::POLL);
172 let ready_ty = subst.type_at(0);
174 if let ty::Adt(ready_def, ready_subst) = ready_ty.kind();
175 if cx.tcx.is_diagnostic_item(sym::Option, ready_def.did);
176 let some_ty = ready_subst.type_at(0);
178 if let ty::Adt(some_def, some_subst) = some_ty.kind();
179 if cx.tcx.is_diagnostic_item(sym::Result, some_def.did);
181 Some(some_subst.type_at(1))