1 use crate::utils::{match_qpath, paths, snippet, span_lint_and_then};
2 use rustc_ast::ast::LitKind;
3 use rustc_errors::Applicability;
4 use rustc_hir::{Arm, Expr, ExprKind, MatchSource, PatKind, QPath};
5 use rustc_lint::{LateContext, LateLintPass};
6 use rustc_session::{declare_lint_pass, declare_tool_lint};
9 /// **What it does:** Lint for redundant pattern matching over `Result` or
12 /// **Why is this bad?** It's more concise and clear to just use the proper
15 /// **Known problems:** None.
20 /// if let Ok(_) = Ok::<i32, i32>(42) {}
21 /// if let Err(_) = Err::<i32, i32>(42) {}
22 /// if let None = None::<()> {}
23 /// if let Some(_) = Some(42) {}
24 /// match Ok::<i32, i32>(42) {
30 /// The more idiomatic use would be:
33 /// if Ok::<i32, i32>(42).is_ok() {}
34 /// if Err::<i32, i32>(42).is_err() {}
35 /// if None::<()>.is_none() {}
36 /// if Some(42).is_some() {}
37 /// Ok::<i32, i32>(42).is_ok();
39 pub REDUNDANT_PATTERN_MATCHING,
41 "use the proper utility function avoiding an `if let`"
44 declare_lint_pass!(RedundantPatternMatching => [REDUNDANT_PATTERN_MATCHING]);
46 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for RedundantPatternMatching {
47 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
48 if let ExprKind::Match(op, arms, ref match_source) = &expr.kind {
50 MatchSource::Normal => find_sugg_for_match(cx, expr, op, arms),
51 MatchSource::IfLetDesugar { contains_else_clause } => {
52 find_sugg_for_if_let(cx, expr, op, arms, *contains_else_clause)
60 fn find_sugg_for_if_let<'a, 'tcx>(
61 cx: &LateContext<'a, 'tcx>,
67 let good_method = match arms[0].pat.kind {
68 PatKind::TupleStruct(ref path, ref patterns, _) if patterns.len() == 1 => {
69 if let PatKind::Wild = patterns[0].kind {
70 if match_qpath(path, &paths::RESULT_OK) {
72 } else if match_qpath(path, &paths::RESULT_ERR) {
74 } else if match_qpath(path, &paths::OPTION_SOME) {
84 PatKind::Path(ref path) if match_qpath(path, &paths::OPTION_NONE) => "is_none()",
89 let maybe_semi = if has_else { "" } else { ";" };
93 REDUNDANT_PATTERN_MATCHING,
95 &format!("redundant pattern matching, consider using `{}`", good_method),
97 let span = expr.span.to(op.span);
101 format!("{}.{}{}", snippet(cx, op.span, "_"), good_method, maybe_semi),
102 Applicability::MaybeIncorrect, // snippet
108 fn find_sugg_for_match<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>, op: &Expr<'_>, arms: &[Arm<'_>]) {
110 let node_pair = (&arms[0].pat.kind, &arms[1].pat.kind);
112 let found_good_method = match node_pair {
114 PatKind::TupleStruct(ref path_left, ref patterns_left, _),
115 PatKind::TupleStruct(ref path_right, ref patterns_right, _),
116 ) if patterns_left.len() == 1 && patterns_right.len() == 1 => {
117 if let (PatKind::Wild, PatKind::Wild) = (&patterns_left[0].kind, &patterns_right[0].kind) {
118 find_good_method_for_match(
131 (PatKind::TupleStruct(ref path_left, ref patterns, _), PatKind::Path(ref path_right))
132 | (PatKind::Path(ref path_left), PatKind::TupleStruct(ref path_right, ref patterns, _))
133 if patterns.len() == 1 =>
135 if let PatKind::Wild = patterns[0].kind {
136 find_good_method_for_match(
152 if let Some(good_method) = found_good_method {
155 REDUNDANT_PATTERN_MATCHING,
157 &format!("redundant pattern matching, consider using `{}`", good_method),
159 let span = expr.span.to(op.span);
163 format!("{}.{}", snippet(cx, op.span, "_"), good_method),
164 Applicability::MaybeIncorrect, // snippet
172 fn find_good_method_for_match<'a>(
174 path_left: &QPath<'_>,
175 path_right: &QPath<'_>,
176 expected_left: &[&str],
177 expected_right: &[&str],
178 should_be_left: &'a str,
179 should_be_right: &'a str,
180 ) -> Option<&'a str> {
181 let body_node_pair = if match_qpath(path_left, expected_left) && match_qpath(path_right, expected_right) {
182 (&(*arms[0].body).kind, &(*arms[1].body).kind)
183 } else if match_qpath(path_right, expected_left) && match_qpath(path_left, expected_right) {
184 (&(*arms[1].body).kind, &(*arms[0].body).kind)
189 match body_node_pair {
190 (ExprKind::Lit(ref lit_left), ExprKind::Lit(ref lit_right)) => match (&lit_left.node, &lit_right.node) {
191 (LitKind::Bool(true), LitKind::Bool(false)) => Some(should_be_left),
192 (LitKind::Bool(false), LitKind::Bool(true)) => Some(should_be_right),