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, LintContext};
8 use rustc_middle::lint::in_external_macro;
9 use rustc_middle::ty::Ty;
10 use rustc_session::{declare_lint_pass, declare_tool_lint};
12 declare_clippy_lint! {
14 /// Checks for pattern matchings that can be expressed using equality.
16 /// ### Why is this bad?
18 /// * It reads better and has less cognitive load because equality won't cause binding.
19 /// * It is a [Yoda condition](https://en.wikipedia.org/wiki/Yoda_conditions). Yoda conditions are widely
20 /// criticized for increasing the cognitive load of reading the code.
21 /// * Equality is a simple bool expression and can be merged with `&&` and `||` and
26 /// if let Some(2) = x {
36 #[clippy::version = "1.57.0"]
39 "using pattern matching instead of equality"
42 declare_lint_pass!(PatternEquality => [EQUATABLE_IF_LET]);
44 /// detects if pattern matches just one thing
45 fn unary_pattern(pat: &Pat<'_>) -> bool {
46 fn array_rec(pats: &[Pat<'_>]) -> bool {
47 pats.iter().all(unary_pattern)
50 PatKind::Slice(_, _, _) | PatKind::Range(_, _, _) | PatKind::Binding(..) | PatKind::Wild | PatKind::Or(_) => {
53 PatKind::Struct(_, a, etc) => !etc && a.iter().all(|x| unary_pattern(x.pat)),
54 PatKind::Tuple(a, etc) | PatKind::TupleStruct(_, a, etc) => {
55 !etc.as_opt_usize().is_some() && array_rec(a)
57 PatKind::Ref(x, _) | PatKind::Box(x) => unary_pattern(x),
58 PatKind::Path(_) | PatKind::Lit(_) => true,
62 fn is_structural_partial_eq<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, other: Ty<'tcx>) -> bool {
63 if let Some(def_id) = cx.tcx.lang_items().eq_trait() {
64 implements_trait(cx, ty, def_id, &[other.into()])
70 impl<'tcx> LateLintPass<'tcx> for PatternEquality {
71 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
73 if !in_external_macro(cx.sess(), expr.span);
74 if let ExprKind::Let(let_expr) = expr.kind;
75 if unary_pattern(let_expr.pat);
76 let exp_ty = cx.typeck_results().expr_ty(let_expr.init);
77 let pat_ty = cx.typeck_results().pat_ty(let_expr.pat);
78 if is_structural_partial_eq(cx, exp_ty, pat_ty);
81 let mut applicability = Applicability::MachineApplicable;
82 let pat_str = match let_expr.pat.kind {
83 PatKind::Struct(..) => format!(
85 snippet_with_context(cx, let_expr.pat.span, expr.span.ctxt(), "..", &mut applicability).0,
87 _ => snippet_with_context(cx, let_expr.pat.span, expr.span.ctxt(), "..", &mut applicability).0.to_string(),
93 "this pattern matching can be expressed using equality",
97 snippet_with_context(cx, let_expr.init.span, expr.span.ctxt(), "..", &mut applicability).0,