1 files changed, 56 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/methods/into_iter_on_ref.rs b/src/tools/clippy/clippy_lints/src/methods/into_iter_on_ref.rs
new file mode 100644
index 000000000..da13b4ba3
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/methods/into_iter_on_ref.rs
@@ -0,0 +1,56 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::is_trait_method;
+use clippy_utils::ty::has_iter_method;
+use if_chain::if_chain;
+use rustc_errors::Applicability;
+use rustc_hir as hir;
+use rustc_lint::LateContext;
+use rustc_middle::ty::{self, Ty};
+use rustc_span::source_map::Span;
+use rustc_span::symbol::{sym, Symbol};
+
+use super::INTO_ITER_ON_REF;
+
+pub(super) fn check(
+    cx: &LateContext<'_>,
+    expr: &hir::Expr<'_>,
+    method_span: Span,
+    method_name: Symbol,
+    args: &[hir::Expr<'_>],
+) {
+    let self_ty = cx.typeck_results().expr_ty_adjusted(&args[0]);
+    if_chain! {
+        if let ty::Ref(..) = self_ty.kind();
+        if method_name == sym::into_iter;
+        if is_trait_method(cx, expr, sym::IntoIterator);
+        if let Some((kind, method_name)) = ty_has_iter_method(cx, self_ty);
+        then {
+            span_lint_and_sugg(
+                cx,
+                INTO_ITER_ON_REF,
+                method_span,
+                &format!(
+                    "this `.into_iter()` call is equivalent to `.{}()` and will not consume the `{}`",
+                    method_name, kind,
+                ),
+                "call directly",
+                method_name.to_string(),
+                Applicability::MachineApplicable,
+            );
+        }
+    }
+}
+
+fn ty_has_iter_method(cx: &LateContext<'_>, self_ref_ty: Ty<'_>) -> Option<(Symbol, &'static str)> {
+    has_iter_method(cx, self_ref_ty).map(|ty_name| {
+        let mutbl = match self_ref_ty.kind() {
+            ty::Ref(_, _, mutbl) => mutbl,
+            _ => unreachable!(),
+        };
+        let method_name = match mutbl {
+            hir::Mutability::Not => "iter",
+            hir::Mutability::Mut => "iter_mut",
+        };
+        (ty_name, method_name)
+    })
+}