1 files changed, 36 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/methods/suspicious_to_owned.rs b/src/tools/clippy/clippy_lints/src/methods/suspicious_to_owned.rs
new file mode 100644
index 000000000..6b306fbf0
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/methods/suspicious_to_owned.rs
@@ -0,0 +1,36 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::is_diag_trait_item;
+use clippy_utils::source::snippet_with_context;
+use if_chain::if_chain;
+use rustc_errors::Applicability;
+use rustc_hir as hir;
+use rustc_lint::LateContext;
+use rustc_middle::ty;
+use rustc_span::sym;
+
+use super::SUSPICIOUS_TO_OWNED;
+
+pub fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, recv: &hir::Expr<'_>) -> bool {
+    if_chain! {
+        if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
+        if is_diag_trait_item(cx, method_def_id, sym::ToOwned);
+        let input_type = cx.typeck_results().expr_ty(expr);
+        if let ty::Adt(adt, _) = cx.typeck_results().expr_ty(expr).kind();
+        if cx.tcx.is_diagnostic_item(sym::Cow, adt.did());
+        then {
+            let mut app = Applicability::MaybeIncorrect;
+            let recv_snip = snippet_with_context(cx, recv.span, expr.span.ctxt(), "..", &mut app).0;
+            span_lint_and_sugg(
+                cx,
+                SUSPICIOUS_TO_OWNED,
+                expr.span,
+                &format!("this `to_owned` call clones the {0} itself and does not cause the {0} contents to become owned", input_type),
+                "consider using, depending on intent",
+                format!("{0}.clone()` or `{0}.into_owned()", recv_snip),
+                app,
+            );
+            return true;
+        }
+    }
+    false
+}