1 files changed, 25 insertions, 5 deletions
diff --git a/src/tools/clippy/clippy_lints/src/drop_forget_ref.rs b/src/tools/clippy/clippy_lints/src/drop_forget_ref.rs
index b35f0b8ca..4721a7b37 100644
--- a/src/tools/clippy/clippy_lints/src/drop_forget_ref.rs
+++ b/src/tools/clippy/clippy_lints/src/drop_forget_ref.rs
@@ -1,7 +1,8 @@
 use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_note};
+use clippy_utils::get_parent_node;
 use clippy_utils::is_must_use_func_call;
 use clippy_utils::ty::{is_copy, is_must_use_ty, is_type_lang_item};
-use rustc_hir::{Expr, ExprKind, LangItem};
+use rustc_hir::{Arm, Expr, ExprKind, LangItem, Node};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::sym;
@@ -202,11 +203,13 @@ impl<'tcx> LateLintPass<'tcx> for DropForgetRef {
             && let Some(fn_name) = cx.tcx.get_diagnostic_name(def_id)
         {
             let arg_ty = cx.typeck_results().expr_ty(arg);
+            let is_copy = is_copy(cx, arg_ty);
+            let drop_is_single_call_in_arm = is_single_call_in_arm(cx, arg, expr);
             let (lint, msg) = match fn_name {
                 sym::mem_drop if arg_ty.is_ref() => (DROP_REF, DROP_REF_SUMMARY),
                 sym::mem_forget if arg_ty.is_ref() => (FORGET_REF, FORGET_REF_SUMMARY),
-                sym::mem_drop if is_copy(cx, arg_ty) => (DROP_COPY, DROP_COPY_SUMMARY),
-                sym::mem_forget if is_copy(cx, arg_ty) => (FORGET_COPY, FORGET_COPY_SUMMARY),
+                sym::mem_drop if is_copy && !drop_is_single_call_in_arm => (DROP_COPY, DROP_COPY_SUMMARY),
+                sym::mem_forget if is_copy => (FORGET_COPY, FORGET_COPY_SUMMARY),
                 sym::mem_drop if is_type_lang_item(cx, arg_ty, LangItem::ManuallyDrop) => {
                     span_lint_and_help(
                         cx,
@@ -221,7 +224,9 @@ impl<'tcx> LateLintPass<'tcx> for DropForgetRef {
                 sym::mem_drop
                     if !(arg_ty.needs_drop(cx.tcx, cx.param_env)
                         || is_must_use_func_call(cx, arg)
-                        || is_must_use_ty(cx, arg_ty)) =>
+                        || is_must_use_ty(cx, arg_ty)
+                        || drop_is_single_call_in_arm
+                        ) =>
                 {
                     (DROP_NON_DROP, DROP_NON_DROP_SUMMARY)
                 },
@@ -236,8 +241,23 @@ impl<'tcx> LateLintPass<'tcx> for DropForgetRef {
                 expr.span,
                 msg,
                 Some(arg.span),
-                &format!("argument has type `{}`", arg_ty),
+                &format!("argument has type `{arg_ty}`"),
             );
         }
     }
 }
+
+// dropping returned value of a function like in the following snippet is considered idiomatic, see
+// #9482 for examples match <var> {
+//     <pat> => drop(fn_with_side_effect_and_returning_some_value()),
+//     ..
+// }
+fn is_single_call_in_arm<'tcx>(cx: &LateContext<'tcx>, arg: &'tcx Expr<'_>, drop_expr: &'tcx Expr<'_>) -> bool {
+    if matches!(arg.kind, ExprKind::Call(..) | ExprKind::MethodCall(..)) {
+        let parent_node = get_parent_node(cx.tcx, drop_expr.hir_id);
+        if let Some(Node::Arm(Arm { body, .. })) = &parent_node {
+            return body.hir_id == drop_expr.hir_id;
+        }
+    }
+    false
+}