Rollup merge of #113231 - Urgau:fix_false_positive_drop_copy, r=Nilstrieb

Fix `dropping_copy_types` lint from linting in match-arm with side-effects

This PR fixes an issue with the `dropping_copy_types` and `dropping_references` lints when not all patterns that can have side-effects were detected and ignored.

Nearly _fixes_ https://github.com/rust-lang/rust/issues/112653 (will need beta-backport to completely fix the issue)
r? ``@Nilstrieb``

2 files changed, 38 insertions, 0 deletions

diff --git a/tests/ui/lint/dropping_copy_types.rs b/tests/ui/lint/dropping_copy_types.rs
index 2937320e5d8..2412222d6d1 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 0d5d484f451..bb02cb75a90 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(())
+    }
+}