src/tools/clippy/clippy_lints/src/methods/filter_next.rs

   1 use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg};
   2 use clippy_utils::source::snippet;
   3 use clippy_utils::ty::implements_trait;
   4 use rustc_errors::Applicability;
   5 use rustc_hir as hir;
   6 use rustc_lint::LateContext;
   7 use rustc_span::sym;
   8
   9 use super::FILTER_NEXT;
  10
  11 /// lint use of `filter().next()` for `Iterators`
  12 pub(super) fn check<'tcx>(
  13     cx: &LateContext<'tcx>,
  14     expr: &'tcx hir::Expr<'_>,
  15     recv: &'tcx hir::Expr<'_>,
  16     filter_arg: &'tcx hir::Expr<'_>,
  17 ) {
  18     // lint if caller of `.filter().next()` is an Iterator
  19     let recv_impls_iterator = cx.tcx.get_diagnostic_item(sym::Iterator).map_or(false, |id| {
  20         implements_trait(cx, cx.typeck_results().expr_ty(recv), id, &[])
  21     });
  22     if recv_impls_iterator {
  23         let msg = "called `filter(..).next()` on an `Iterator`. This is more succinctly expressed by calling \
  24                    `.find(..)` instead";
  25         let filter_snippet = snippet(cx, filter_arg.span, "..");
  26         if filter_snippet.lines().count() <= 1 {
  27             let iter_snippet = snippet(cx, recv.span, "..");
  28             // add note if not multi-line
  29             span_lint_and_sugg(
  30                 cx,
  31                 FILTER_NEXT,
  32                 expr.span,
  33                 msg,
  34                 "try this",
  35                 format!("{}.find({})", iter_snippet, filter_snippet),
  36                 Applicability::MachineApplicable,
  37             );
  38         } else {
  39             span_lint(cx, FILTER_NEXT, expr.span, msg);
  40         }
  41     }
  42 }