1 use crate::utils::{match_qpath, paths, snippet, span_lint_and_then};
3 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
4 use rustc::{declare_tool_lint, lint_array};
5 use rustc_errors::Applicability;
6 use syntax::ast::LitKind;
10 /// **What it does:** Lint for redundant pattern matching over `Result` or
13 /// **Why is this bad?** It's more concise and clear to just use the proper
16 /// **Known problems:** None.
21 /// if let Ok(_) = Ok::<i32, i32>(42) {}
22 /// if let Err(_) = Err::<i32, i32>(42) {}
23 /// if let None = None::<()> {}
24 /// if let Some(_) = Some(42) {}
25 /// match Ok::<i32, i32>(42) {
31 /// The more idiomatic use would be:
34 /// if Ok::<i32, i32>(42).is_ok() {}
35 /// if Err::<i32, i32>(42).is_err() {}
36 /// if None::<()>.is_none() {}
37 /// if Some(42).is_some() {}
38 /// Ok::<i32, i32>(42).is_ok();
40 pub REDUNDANT_PATTERN_MATCHING,
42 "use the proper utility function avoiding an `if let`"
45 #[derive(Copy, Clone)]
48 impl LintPass for Pass {
49 fn get_lints(&self) -> LintArray {
50 lint_array!(REDUNDANT_PATTERN_MATCHING)
53 fn name(&self) -> &'static str {
54 "RedundantPatternMatching"
58 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
59 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
60 if let ExprKind::Match(ref op, ref arms, ref match_source) = expr.node {
62 MatchSource::Normal => find_sugg_for_match(cx, expr, op, arms),
63 MatchSource::IfLetDesugar { .. } => find_sugg_for_if_let(cx, expr, op, arms),
70 fn find_sugg_for_if_let<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr, op: &P<Expr>, arms: &HirVec<Arm>) {
71 if arms[0].pats.len() == 1 {
72 let good_method = match arms[0].pats[0].node {
73 PatKind::TupleStruct(ref path, ref patterns, _) if patterns.len() == 1 => {
74 if let PatKind::Wild = patterns[0].node {
75 if match_qpath(path, &paths::RESULT_OK) {
77 } else if match_qpath(path, &paths::RESULT_ERR) {
79 } else if match_qpath(path, &paths::OPTION_SOME) {
89 PatKind::Path(ref path) if match_qpath(path, &paths::OPTION_NONE) => "is_none()",
96 REDUNDANT_PATTERN_MATCHING,
98 &format!("redundant pattern matching, consider using `{}`", good_method),
100 let span = expr.span.to(op.span);
104 format!("if {}.{}", snippet(cx, op.span, "_"), good_method),
105 Applicability::MachineApplicable, // snippet
114 fn find_sugg_for_match<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr, op: &P<Expr>, arms: &HirVec<Arm>) {
116 let node_pair = (&arms[0].pats[0].node, &arms[1].pats[0].node);
118 let found_good_method = match node_pair {
120 PatKind::TupleStruct(ref path_left, ref patterns_left, _),
121 PatKind::TupleStruct(ref path_right, ref patterns_right, _),
122 ) if patterns_left.len() == 1 && patterns_right.len() == 1 => {
123 if let (PatKind::Wild, PatKind::Wild) = (&patterns_left[0].node, &patterns_right[0].node) {
124 find_good_method_for_match(
137 (PatKind::TupleStruct(ref path_left, ref patterns, _), PatKind::Path(ref path_right))
138 | (PatKind::Path(ref path_left), PatKind::TupleStruct(ref path_right, ref patterns, _))
139 if patterns.len() == 1 =>
141 if let PatKind::Wild = patterns[0].node {
142 find_good_method_for_match(
158 if let Some(good_method) = found_good_method {
161 REDUNDANT_PATTERN_MATCHING,
163 &format!("redundant pattern matching, consider using `{}`", good_method),
165 let span = expr.span.to(op.span);
169 format!("{}.{}", snippet(cx, op.span, "_"), good_method),
170 Applicability::MachineApplicable, // snippet
180 fn find_good_method_for_match<'a>(
184 expected_left: &[&str],
185 expected_right: &[&str],
186 should_be_left: &'a str,
187 should_be_right: &'a str,
188 ) -> Option<&'a str> {
189 let body_node_pair = if match_qpath(path_left, expected_left) && match_qpath(path_right, expected_right) {
190 (&(*arms[0].body).node, &(*arms[1].body).node)
191 } else if match_qpath(path_right, expected_left) && match_qpath(path_left, expected_right) {
192 (&(*arms[1].body).node, &(*arms[0].body).node)
197 match body_node_pair {
198 (ExprKind::Lit(ref lit_left), ExprKind::Lit(ref lit_right)) => match (&lit_left.node, &lit_right.node) {
199 (LitKind::Bool(true), LitKind::Bool(false)) => Some(should_be_left),
200 (LitKind::Bool(false), LitKind::Bool(true)) => Some(should_be_right),