clippy_lints/src/matches/match_like_matches.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::source::snippet_with_applicability;
   3 use clippy_utils::{higher, is_wild};
   4 use rustc_ast::{Attribute, LitKind};
   5 use rustc_errors::Applicability;
   6 use rustc_hir::{BorrowKind, Expr, ExprKind, Guard, MatchSource, Pat};
   7 use rustc_lint::LateContext;
   8 use rustc_middle::ty;
   9 use rustc_span::source_map::Spanned;
  10
  11 use super::MATCH_LIKE_MATCHES_MACRO;
  12
  13 /// Lint a `match` or `if let .. { .. } else { .. }` expr that could be replaced by `matches!`
  14 pub(crate) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
  15     if let Some(higher::IfLet {
  16         let_pat,
  17         let_expr,
  18         if_then,
  19         if_else: Some(if_else),
  20     }) = higher::IfLet::hir(cx, expr)
  21     {
  22         return find_matches_sugg(
  23             cx,
  24             let_expr,
  25             IntoIterator::into_iter([(&[][..], Some(let_pat), if_then, None), (&[][..], None, if_else, None)]),
  26             expr,
  27             true,
  28         );
  29     }
  30
  31     if let ExprKind::Match(scrut, arms, MatchSource::Normal) = expr.kind {
  32         return find_matches_sugg(
  33             cx,
  34             scrut,
  35             arms.iter().map(|arm| {
  36                 (
  37                     cx.tcx.hir().attrs(arm.hir_id),
  38                     Some(arm.pat),
  39                     arm.body,
  40                     arm.guard.as_ref(),
  41                 )
  42             }),
  43             expr,
  44             false,
  45         );
  46     }
  47
  48     false
  49 }
  50
  51 /// Lint a `match` or `if let` for replacement by `matches!`
  52 fn find_matches_sugg<'a, 'b, I>(
  53     cx: &LateContext<'_>,
  54     ex: &Expr<'_>,
  55     mut iter: I,
  56     expr: &Expr<'_>,
  57     is_if_let: bool,
  58 ) -> bool
  59 where
  60     'b: 'a,
  61     I: Clone
  62         + DoubleEndedIterator
  63         + ExactSizeIterator
  64         + Iterator<
  65             Item = (
  66                 &'a [Attribute],
  67                 Option<&'a Pat<'b>>,
  68                 &'a Expr<'b>,
  69                 Option<&'a Guard<'b>>,
  70             ),
  71         >,
  72 {
  73     if_chain! {
  74         if iter.len() >= 2;
  75         if cx.typeck_results().expr_ty(expr).is_bool();
  76         if let Some((_, last_pat_opt, last_expr, _)) = iter.next_back();
  77         let iter_without_last = iter.clone();
  78         if let Some((first_attrs, _, first_expr, first_guard)) = iter.next();
  79         if let Some(b0) = find_bool_lit(&first_expr.kind, is_if_let);
  80         if let Some(b1) = find_bool_lit(&last_expr.kind, is_if_let);
  81         if b0 != b1;
  82         if first_guard.is_none() || iter.len() == 0;
  83         if first_attrs.is_empty();
  84         if iter
  85             .all(|arm| {
  86                 find_bool_lit(&arm.2.kind, is_if_let).map_or(false, |b| b == b0) && arm.3.is_none() && arm.0.is_empty()
  87             });
  88         then {
  89             if let Some(last_pat) = last_pat_opt {
  90                 if !is_wild(last_pat) {
  91                     return false;
  92                 }
  93             }
  94
  95             // The suggestion may be incorrect, because some arms can have `cfg` attributes
  96             // evaluated into `false` and so such arms will be stripped before.
  97             let mut applicability = Applicability::MaybeIncorrect;
  98             let pat = {
  99                 use itertools::Itertools as _;
 100                 iter_without_last
 101                     .filter_map(|arm| {
 102                         let pat_span = arm.1?.span;
 103                         Some(snippet_with_applicability(cx, pat_span, "..", &mut applicability))
 104                     })
 105                     .join(" | ")
 106             };
 107             let pat_and_guard = if let Some(Guard::If(g)) = first_guard {
 108                 format!("{} if {}", pat, snippet_with_applicability(cx, g.span, "..", &mut applicability))
 109             } else {
 110                 pat
 111             };
 112
 113             // strip potential borrows (#6503), but only if the type is a reference
 114             let mut ex_new = ex;
 115             if let ExprKind::AddrOf(BorrowKind::Ref, .., ex_inner) = ex.kind {
 116                 if let ty::Ref(..) = cx.typeck_results().expr_ty(ex_inner).kind() {
 117                     ex_new = ex_inner;
 118                 }
 119             };
 120             span_lint_and_sugg(
 121                 cx,
 122                 MATCH_LIKE_MATCHES_MACRO,
 123                 expr.span,
 124                 &format!("{} expression looks like `matches!` macro", if is_if_let { "if let .. else" } else { "match" }),
 125                 "try this",
 126                 format!(
 127                     "{}matches!({}, {})",
 128                     if b0 { "" } else { "!" },
 129                     snippet_with_applicability(cx, ex_new.span, "..", &mut applicability),
 130                     pat_and_guard,
 131                 ),
 132                 applicability,
 133             );
 134             true
 135         } else {
 136             false
 137         }
 138     }
 139 }
 140
 141 /// Extract a `bool` or `{ bool }`
 142 fn find_bool_lit(ex: &ExprKind<'_>, is_if_let: bool) -> Option<bool> {
 143     match ex {
 144         ExprKind::Lit(Spanned {
 145             node: LitKind::Bool(b), ..
 146         }) => Some(*b),
 147         ExprKind::Block(
 148             rustc_hir::Block {
 149                 stmts: &[],
 150                 expr: Some(exp),
 151                 ..
 152             },
 153             _,
 154         ) if is_if_let => {
 155             if let ExprKind::Lit(Spanned {
 156                 node: LitKind::Bool(b), ..
 157             }) = exp.kind
 158             {
 159                 Some(b)
 160             } else {
 161                 None
 162             }
 163         },
 164         _ => None,
 165     }
 166 }