1 use clippy_utils::diagnostics::span_lint_and_sugg;
2 use clippy_utils::source::snippet_with_context;
3 use clippy_utils::ty::implements_trait;
4 use if_chain::if_chain;
5 use rustc_errors::Applicability;
6 use rustc_hir::{Expr, ExprKind, Pat, PatKind};
7 use rustc_lint::{LateContext, LateLintPass};
8 use rustc_middle::ty::Ty;
9 use rustc_session::{declare_lint_pass, declare_tool_lint};
11 declare_clippy_lint! {
13 /// Checks for pattern matchings that can be expressed using equality.
15 /// ### Why is this bad?
17 /// * It reads better and has less cognitive load because equality won't cause binding.
18 /// * It is a [Yoda condition](https://en.wikipedia.org/wiki/Yoda_conditions). Yoda conditions are widely
19 /// criticized for increasing the cognitive load of reading the code.
20 /// * Equality is a simple bool expression and can be merged with `&&` and `||` and
25 /// if let Some(2) = x {
37 "using pattern matching instead of equality"
40 declare_lint_pass!(PatternEquality => [EQUATABLE_IF_LET]);
42 /// detects if pattern matches just one thing
43 fn unary_pattern(pat: &Pat<'_>) -> bool {
44 fn array_rec(pats: &[Pat<'_>]) -> bool {
45 pats.iter().all(unary_pattern)
48 PatKind::Slice(_, _, _) | PatKind::Range(_, _, _) | PatKind::Binding(..) | PatKind::Wild | PatKind::Or(_) => {
51 PatKind::Struct(_, a, etc) => !etc && a.iter().all(|x| unary_pattern(x.pat)),
52 PatKind::Tuple(a, etc) | PatKind::TupleStruct(_, a, etc) => !etc.is_some() && array_rec(a),
53 PatKind::Ref(x, _) | PatKind::Box(x) => unary_pattern(x),
54 PatKind::Path(_) | PatKind::Lit(_) => true,
58 fn is_structural_partial_eq(cx: &LateContext<'tcx>, ty: Ty<'tcx>, other: Ty<'tcx>) -> bool {
59 if let Some(def_id) = cx.tcx.lang_items().eq_trait() {
60 implements_trait(cx, ty, def_id, &[other.into()])
66 impl<'tcx> LateLintPass<'tcx> for PatternEquality {
67 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
69 if let ExprKind::Let(pat, exp, _) = expr.kind;
70 if unary_pattern(pat);
71 let exp_ty = cx.typeck_results().expr_ty(exp);
72 let pat_ty = cx.typeck_results().pat_ty(pat);
73 if is_structural_partial_eq(cx, exp_ty, pat_ty);
76 let mut applicability = Applicability::MachineApplicable;
77 let pat_str = match pat.kind {
78 PatKind::Struct(..) => format!(
80 snippet_with_context(cx, pat.span, expr.span.ctxt(), "..", &mut applicability).0,
82 _ => snippet_with_context(cx, pat.span, expr.span.ctxt(), "..", &mut applicability).0.to_string(),
88 "this pattern matching can be expressed using equality",
92 snippet_with_context(cx, exp.span, expr.span.ctxt(), "..", &mut applicability).0,