clippy_lints/src/loops/for_kv_map.rs

   1 use super::FOR_KV_MAP;
   2 use clippy_utils::diagnostics::{multispan_sugg, span_lint_and_then};
   3 use clippy_utils::source::snippet;
   4 use clippy_utils::sugg;
   5 use clippy_utils::ty::is_type_diagnostic_item;
   6 use clippy_utils::visitors::LocalUsedVisitor;
   7 use rustc_hir::{BorrowKind, Expr, ExprKind, Mutability, Pat, PatKind};
   8 use rustc_lint::LateContext;
   9 use rustc_middle::ty;
  10 use rustc_span::sym;
  11
  12 /// Checks for the `FOR_KV_MAP` lint.
  13 pub(super) fn check<'tcx>(
  14     cx: &LateContext<'tcx>,
  15     pat: &'tcx Pat<'_>,
  16     arg: &'tcx Expr<'_>,
  17     body: &'tcx Expr<'_>,
  18     expr: &'tcx Expr<'_>,
  19 ) {
  20     let pat_span = pat.span;
  21
  22     if let PatKind::Tuple(pat, _) = pat.kind {
  23         if pat.len() == 2 {
  24             let arg_span = arg.span;
  25             let (new_pat_span, kind, ty, mutbl) = match *cx.typeck_results().expr_ty(arg).kind() {
  26                 ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
  27                     (key, _) if pat_is_wild(cx, key, body) => (pat[1].span, "value", ty, mutbl),
  28                     (_, value) if pat_is_wild(cx, value, body) => (pat[0].span, "key", ty, Mutability::Not),
  29                     _ => return,
  30                 },
  31                 _ => return,
  32             };
  33             let mutbl = match mutbl {
  34                 Mutability::Not => "",
  35                 Mutability::Mut => "_mut",
  36             };
  37             let arg = match arg.kind {
  38                 ExprKind::AddrOf(BorrowKind::Ref, _, expr) => expr,
  39                 _ => arg,
  40             };
  41
  42             if is_type_diagnostic_item(cx, ty, sym::hashmap_type) || is_type_diagnostic_item(cx, ty, sym::BTreeMap) {
  43                 span_lint_and_then(
  44                     cx,
  45                     FOR_KV_MAP,
  46                     expr.span,
  47                     &format!("you seem to want to iterate on a map's {}s", kind),
  48                     |diag| {
  49                         let map = sugg::Sugg::hir(cx, arg, "map");
  50                         multispan_sugg(
  51                             diag,
  52                             "use the corresponding method",
  53                             vec![
  54                                 (pat_span, snippet(cx, new_pat_span, kind).into_owned()),
  55                                 (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
  56                             ],
  57                         );
  58                     },
  59                 );
  60             }
  61         }
  62     }
  63 }
  64
  65 /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
  66 fn pat_is_wild<'tcx>(cx: &LateContext<'tcx>, pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool {
  67     match *pat {
  68         PatKind::Wild => true,
  69         PatKind::Binding(_, id, ident, None) if ident.as_str().starts_with('_') => {
  70             !LocalUsedVisitor::new(cx, id).check_expr(body)
  71         },
  72         _ => false,
  73     }
  74 }