1 files changed, 37 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/methods/bytes_count_to_len.rs b/src/tools/clippy/clippy_lints/src/methods/bytes_count_to_len.rs
new file mode 100644
index 000000000..fcfc25b52
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/methods/bytes_count_to_len.rs
@@ -0,0 +1,37 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::snippet_with_applicability;
+use clippy_utils::ty::is_type_diagnostic_item;
+use if_chain::if_chain;
+use rustc_errors::Applicability;
+use rustc_hir as hir;
+use rustc_lint::LateContext;
+use rustc_span::sym;
+
+use super::BYTES_COUNT_TO_LEN;
+
+pub(super) fn check<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx hir::Expr<'_>,
+    count_recv: &'tcx hir::Expr<'_>,
+    bytes_recv: &'tcx hir::Expr<'_>,
+) {
+    if_chain! {
+        if let Some(bytes_id) = cx.typeck_results().type_dependent_def_id(count_recv.hir_id);
+        if let Some(impl_id) = cx.tcx.impl_of_method(bytes_id);
+        if cx.tcx.type_of(impl_id).is_str();
+        let ty = cx.typeck_results().expr_ty(bytes_recv).peel_refs();
+        if ty.is_str() || is_type_diagnostic_item(cx, ty, sym::String);
+        then {
+            let mut applicability = Applicability::MachineApplicable;
+            span_lint_and_sugg(
+                cx,
+                BYTES_COUNT_TO_LEN,
+                expr.span,
+                "using long and hard to read `.bytes().count()`",
+                "consider calling `.len()` instead",
+                format!("{}.len()", snippet_with_applicability(cx, bytes_recv.span, "..", &mut applicability)),
+                applicability
+            );
+        }
+    };
+}