1 use clippy_utils::diagnostics::span_lint_and_sugg;
2 use clippy_utils::source::{expr_block, snippet};
3 use clippy_utils::ty::{implements_trait, is_type_diagnostic_item, peel_mid_ty_refs};
4 use clippy_utils::{is_lint_allowed, is_unit_expr, is_wild, peel_blocks, peel_hir_pat_refs, peel_n_hir_expr_refs};
6 use rustc_errors::Applicability;
7 use rustc_hir::{Arm, BindingAnnotation, Block, Expr, ExprKind, Pat, PatKind};
8 use rustc_lint::LateContext;
9 use rustc_middle::ty::{self, Ty};
12 use super::{MATCH_BOOL, SINGLE_MATCH, SINGLE_MATCH_ELSE};
15 pub(crate) fn check(cx: &LateContext<'_>, ex: &Expr<'_>, arms: &[Arm<'_>], expr: &Expr<'_>) {
16 if arms.len() == 2 && arms[0].guard.is_none() && arms[1].guard.is_none() {
17 if expr.span.from_expansion() {
18 // Don't lint match expressions present in
22 if let PatKind::Or(..) = arms[0].pat.kind {
23 // don't lint for or patterns for now, this makes
24 // the lint noisy in unnecessary situations
27 let els = arms[1].body;
28 let els = if is_unit_expr(peel_blocks(els)) {
30 } else if let ExprKind::Block(Block { stmts, expr: block_expr, .. }, _) = els.kind {
31 if stmts.len() == 1 && block_expr.is_none() || stmts.is_empty() && block_expr.is_some() {
32 // single statement/expr "else" block, don't lint
35 // block with 2+ statements or 1 expr and 1+ statement
38 // not a block, don't lint
42 let ty = cx.typeck_results().expr_ty(ex);
43 if *ty.kind() != ty::Bool || is_lint_allowed(cx, MATCH_BOOL, ex.hir_id) {
44 check_single_pattern(cx, ex, arms, expr, els);
45 check_opt_like(cx, ex, arms, expr, ty, els);
50 fn check_single_pattern(
55 els: Option<&Expr<'_>>,
57 if is_wild(arms[1].pat) {
58 report_single_pattern(cx, ex, arms, expr, els);
62 fn report_single_pattern(
67 els: Option<&Expr<'_>>,
69 let lint = if els.is_some() { SINGLE_MATCH_ELSE } else { SINGLE_MATCH };
70 let els_str = els.map_or(String::new(), |els| {
71 format!(" else {}", expr_block(cx, els, None, "..", Some(expr.span)))
74 let (pat, pat_ref_count) = peel_hir_pat_refs(arms[0].pat);
75 let (msg, sugg) = if_chain! {
76 if let PatKind::Path(_) | PatKind::Lit(_) = pat.kind;
77 let (ty, ty_ref_count) = peel_mid_ty_refs(cx.typeck_results().expr_ty(ex));
78 if let Some(spe_trait_id) = cx.tcx.lang_items().structural_peq_trait();
79 if let Some(pe_trait_id) = cx.tcx.lang_items().eq_trait();
80 if ty.is_integral() || ty.is_char() || ty.is_str()
81 || (implements_trait(cx, ty, spe_trait_id, &[])
82 && implements_trait(cx, ty, pe_trait_id, &[ty.into()]));
84 // scrutinee derives PartialEq and the pattern is a constant.
85 let pat_ref_count = match pat.kind {
86 // string literals are already a reference.
87 PatKind::Lit(Expr { kind: ExprKind::Lit(lit), .. }) if lit.node.is_str() => pat_ref_count + 1,
90 // References are only implicitly added to the pattern, so no overflow here.
91 // e.g. will work: match &Some(_) { Some(_) => () }
92 // will not: match Some(_) { &Some(_) => () }
93 let ref_count_diff = ty_ref_count - pat_ref_count;
95 // Try to remove address of expressions first.
96 let (ex, removed) = peel_n_hir_expr_refs(ex, ref_count_diff);
97 let ref_count_diff = ref_count_diff - removed;
99 let msg = "you seem to be trying to use `match` for an equality check. Consider using `if`";
101 "if {} == {}{} {}{els_str}",
102 snippet(cx, ex.span, ".."),
103 // PartialEq for different reference counts may not exist.
104 "&".repeat(ref_count_diff),
105 snippet(cx, arms[0].pat.span, ".."),
106 expr_block(cx, arms[0].body, None, "..", Some(expr.span)),
110 let msg = "you seem to be trying to use `match` for destructuring a single pattern. Consider using `if let`";
112 "if let {} = {} {}{els_str}",
113 snippet(cx, arms[0].pat.span, ".."),
114 snippet(cx, ex.span, ".."),
115 expr_block(cx, arms[0].body, None, "..", Some(expr.span)),
128 Applicability::HasPlaceholders,
132 fn check_opt_like<'a>(
133 cx: &LateContext<'a>,
138 els: Option<&Expr<'_>>,
140 // We don't want to lint if the second arm contains an enum which could
141 // have more variants in the future.
142 if form_exhaustive_matches(cx, ty, arms[0].pat, arms[1].pat) {
143 report_single_pattern(cx, ex, arms, expr, els);
147 /// Returns `true` if all of the types in the pattern are enums which we know
148 /// won't be expanded in the future
149 fn pat_in_candidate_enum<'a>(cx: &LateContext<'a>, ty: Ty<'a>, pat: &Pat<'_>) -> bool {
150 let mut paths_and_types = Vec::new();
151 collect_pat_paths(&mut paths_and_types, cx, pat, ty);
152 paths_and_types.iter().all(|ty| in_candidate_enum(cx, *ty))
155 /// Returns `true` if the given type is an enum we know won't be expanded in the future
156 fn in_candidate_enum(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
157 // list of candidate `Enum`s we know will never get any more members
158 let candidates = [sym::Cow, sym::Option, sym::Result];
160 for candidate_ty in candidates {
161 if is_type_diagnostic_item(cx, ty, candidate_ty) {
168 /// Collects types from the given pattern
169 fn collect_pat_paths<'a>(acc: &mut Vec<Ty<'a>>, cx: &LateContext<'a>, pat: &Pat<'_>, ty: Ty<'a>) {
171 PatKind::Tuple(inner, _) => inner.iter().for_each(|p| {
172 let p_ty = cx.typeck_results().pat_ty(p);
173 collect_pat_paths(acc, cx, p, p_ty);
175 PatKind::TupleStruct(..) | PatKind::Binding(BindingAnnotation::NONE, .., None) | PatKind::Path(_) => {
182 /// Returns true if the given arm of pattern matching contains wildcard patterns.
183 fn contains_only_wilds(pat: &Pat<'_>) -> bool {
185 PatKind::Wild => true,
186 PatKind::Tuple(inner, _) | PatKind::TupleStruct(_, inner, ..) => inner.iter().all(contains_only_wilds),
191 /// Returns true if the given patterns forms only exhaustive matches that don't contain enum
192 /// patterns without a wildcard.
193 fn form_exhaustive_matches<'a>(cx: &LateContext<'a>, ty: Ty<'a>, left: &Pat<'_>, right: &Pat<'_>) -> bool {
194 match (&left.kind, &right.kind) {
195 (PatKind::Wild, _) | (_, PatKind::Wild) => true,
196 (PatKind::Tuple(left_in, left_pos), PatKind::Tuple(right_in, right_pos)) => {
197 // We don't actually know the position and the presence of the `..` (dotdot) operator
198 // in the arms, so we need to evaluate the correct offsets here in order to iterate in
199 // both arms at the same time.
200 let left_pos = left_pos.as_opt_usize();
201 let right_pos = right_pos.as_opt_usize();
203 left_in.len() + usize::from(left_pos.is_some()),
204 right_in.len() + usize::from(right_pos.is_some()),
206 let mut left_pos = left_pos.unwrap_or(usize::MAX);
207 let mut right_pos = right_pos.unwrap_or(usize::MAX);
208 let mut left_dot_space = 0;
209 let mut right_dot_space = 0;
211 let mut found_dotdot = false;
214 if left_dot_space < len - left_in.len() {
220 right_dot_space += 1;
221 if right_dot_space < len - right_in.len() {
229 if !contains_only_wilds(&left_in[i - left_dot_space])
230 && !contains_only_wilds(&right_in[i - right_dot_space])
237 (PatKind::TupleStruct(..), PatKind::Path(_)) => pat_in_candidate_enum(cx, ty, right),
238 (PatKind::TupleStruct(..), PatKind::TupleStruct(_, inner, _)) => {
239 pat_in_candidate_enum(cx, ty, right) && inner.iter().all(contains_only_wilds)