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| 1 | +use clippy_utils::diagnostics::span_lint_and_sugg; |
| 2 | +use clippy_utils::source::snippet_with_applicability; |
| 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}; |
| 10 | + |
| 11 | +declare_clippy_lint! { |
| 12 | + /// ### What it does |
| 13 | + /// Checks for pattern matchings that can be expressed using equality. |
| 14 | + /// |
| 15 | + /// ### Why is this bad? |
| 16 | + /// |
| 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 |
| 21 | + /// reuse if blocks |
| 22 | + /// |
| 23 | + /// ### Example |
| 24 | + /// ```rust,ignore |
| 25 | + /// if let Some(2) = x { |
| 26 | + /// do_thing(); |
| 27 | + /// } |
| 28 | + /// ``` |
| 29 | + /// Should be written |
| 30 | + /// ```rust,ignore |
| 31 | + /// if x == Some(2) { |
| 32 | + /// do_thing(); |
| 33 | + /// } |
| 34 | + /// ``` |
| 35 | + pub EQUATABLE_IF_LET, |
| 36 | + nursery, |
| 37 | + "using pattern matching instead of equality" |
| 38 | +} |
| 39 | + |
| 40 | +declare_lint_pass!(PatternEquality => [EQUATABLE_IF_LET]); |
| 41 | + |
| 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) |
| 46 | + } |
| 47 | + match &pat.kind { |
| 48 | + PatKind::Slice(_, _, _) | PatKind::Range(_, _, _) | PatKind::Binding(..) | PatKind::Wild | PatKind::Or(_) => { |
| 49 | + false |
| 50 | + }, |
| 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, |
| 55 | + } |
| 56 | +} |
| 57 | + |
| 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()]) |
| 61 | + } else { |
| 62 | + false |
| 63 | + } |
| 64 | +} |
| 65 | + |
| 66 | +impl<'tcx> LateLintPass<'tcx> for PatternEquality { |
| 67 | + fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) { |
| 68 | + if_chain! { |
| 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); |
| 74 | + then { |
| 75 | + |
| 76 | + let mut applicability = Applicability::MachineApplicable; |
| 77 | + let pat_str = match pat.kind { |
| 78 | + PatKind::Struct(..) => format!( |
| 79 | + "({})", |
| 80 | + snippet_with_applicability(cx, pat.span, "..", &mut applicability), |
| 81 | + ), |
| 82 | + _ => snippet_with_applicability(cx, pat.span, "..", &mut applicability).to_string(), |
| 83 | + }; |
| 84 | + span_lint_and_sugg( |
| 85 | + cx, |
| 86 | + EQUATABLE_IF_LET, |
| 87 | + expr.span, |
| 88 | + "this pattern matching can be expressed using equality", |
| 89 | + "try", |
| 90 | + format!( |
| 91 | + "{} == {}", |
| 92 | + snippet_with_applicability(cx, exp.span, "..", &mut applicability), |
| 93 | + pat_str, |
| 94 | + ), |
| 95 | + applicability, |
| 96 | + ); |
| 97 | + } |
| 98 | + } |
| 99 | + } |
| 100 | +} |
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