From 908574b5e761fca6e0b03ef4e2c8640fcff1218a Mon Sep 17 00:00:00 2001
From: Urgau <urgau@numericable.fr>
Date: Sat, 1 Jul 2023 16:05:55 +0200
Subject: [PATCH] Fix dropping_copy_types lint from linting in match-arm with
 side-effects

---
 .../rustc_lint/src/drop_forget_useless.rs     |  2 +-
 tests/ui/lint/dropping_copy_types.rs          | 19 +++++++++++++++++++
 tests/ui/lint/dropping_references.rs          | 19 +++++++++++++++++++
 3 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/compiler/rustc_lint/src/drop_forget_useless.rs b/compiler/rustc_lint/src/drop_forget_useless.rs
index 4cea6169dc3d9..467f53d445c15 100644
--- a/compiler/rustc_lint/src/drop_forget_useless.rs
+++ b/compiler/rustc_lint/src/drop_forget_useless.rs
@@ -194,7 +194,7 @@ fn is_single_call_in_arm<'tcx>(
     arg: &'tcx Expr<'_>,
     drop_expr: &'tcx Expr<'_>,
 ) -> bool {
-    if matches!(arg.kind, ExprKind::Call(..) | ExprKind::MethodCall(..)) {
+    if arg.can_have_side_effects() {
         let parent_node = cx.tcx.hir().find_parent(drop_expr.hir_id);
         if let Some(Node::Arm(Arm { body, .. })) = &parent_node {
             return body.hir_id == drop_expr.hir_id;
diff --git a/tests/ui/lint/dropping_copy_types.rs b/tests/ui/lint/dropping_copy_types.rs
index 2937320e5d833..2412222d6d16d 100644
--- a/tests/ui/lint/dropping_copy_types.rs
+++ b/tests/ui/lint/dropping_copy_types.rs
@@ -77,3 +77,22 @@ fn issue9482(x: u8) {
         _ => (),
     }
 }
+
+fn issue112653() {
+    fn foo() -> Result<u8, ()> {
+        println!("doing foo");
+        Ok(0) // result is not always useful, the side-effect matters
+    }
+    fn bar() {
+        println!("doing bar");
+    }
+
+    fn stuff() -> Result<(), ()> {
+        match 42 {
+            0 => drop(foo()?),  // drop is needed because we only care about side-effects
+            1 => bar(),
+            _ => (),  // doing nothing (no side-effects needed here)
+        }
+        Ok(())
+    }
+}
diff --git a/tests/ui/lint/dropping_references.rs b/tests/ui/lint/dropping_references.rs
index 0d5d484f4517f..bb02cb75a9014 100644
--- a/tests/ui/lint/dropping_references.rs
+++ b/tests/ui/lint/dropping_references.rs
@@ -97,3 +97,22 @@ fn issue10122(x: u8) {
         _ => (),
     }
 }
+
+fn issue112653() {
+    fn foo() -> Result<&'static u8, ()> {
+        println!("doing foo");
+        Ok(&0) // result is not always useful, the side-effect matters
+    }
+    fn bar() {
+        println!("doing bar");
+    }
+
+    fn stuff() -> Result<(), ()> {
+        match 42 {
+            0 => drop(foo()?),  // drop is needed because we only care about side-effects
+            1 => bar(),
+            _ => (),  // doing nothing (no side-effects needed here)
+        }
+        Ok(())
+    }
+}