Shorten lifetime of panic temporaries in panic_fmt case

Author: dtolnay

library/core/src/panic.rs

@@ -35,9 +35,11 @@ pub macro panic_2015 {
     ("{}", $arg:expr $(,)?) => (
         $crate::panicking::panic_display(&$arg)
     ),
-    ($fmt:expr, $($arg:tt)+) => (
-        $crate::panicking::panic_fmt($crate::const_format_args!($fmt, $($arg)+))
-    ),
+    ($fmt:expr, $($arg:tt)+) => ({
+        // Semicolon to prevent temporaries inside the formatting machinery from
+        // being considered alive in the caller after the panic_fmt call.
+        $crate::panicking::panic_fmt($crate::const_format_args!($fmt, $($arg)+));
+    }),
 }
 
 #[doc(hidden)]
@@ -53,9 +55,11 @@ pub macro panic_2021 {
     ("{}", $arg:expr $(,)?) => (
         $crate::panicking::panic_display(&$arg)
     ),
-    ($($t:tt)+) => (
-        $crate::panicking::panic_fmt($crate::const_format_args!($($t)+))
-    ),
+    ($($t:tt)+) => ({
+        // Semicolon to prevent temporaries inside the formatting machinery from
+        // being considered alive in the caller after the panic_fmt call.
+        $crate::panicking::panic_fmt($crate::const_format_args!($($t)+));
+    }),
 }
 
 #[doc(hidden)]

library/std/src/panic.rs

@@ -26,7 +26,9 @@ pub macro panic_2015 {
         $crate::rt::panic_display(&$arg)
     }),
     ($fmt:expr, $($arg:tt)+) => ({
-        $crate::rt::panic_fmt($crate::const_format_args!($fmt, $($arg)+))
+        // Semicolon to prevent temporaries inside the formatting machinery from
+        // being considered alive in the caller after the panic_fmt call.
+        $crate::rt::panic_fmt($crate::const_format_args!($fmt, $($arg)+));
     }),
 }
 

tests/ui/macros/panic-temporaries.rs

@@ -1,4 +1,4 @@
-// check-fail
+// check-pass
 // edition:2021
 
 #![allow(unreachable_code)]
@@ -15,5 +15,5 @@ async fn g() {
 fn require_send(_: impl Send) {}
 
 fn main() {
-    require_send(g()); //~ future cannot be sent between threads safely
+    require_send(g());
 }

tests/ui/macros/panic-temporaries.stderr

@@ -26,7 +26,7 @@ fn arbitrary_consuming_method_for_demonstration_purposes() {
 
                 {
                     ::std::rt::panic_fmt(format_args!("Assertion failed: elem as usize\nWith captures:\n  elem = {0:?}\n",
-                            __capture0))
+                            __capture0));
                 }
             }
     };
@@ -42,7 +42,7 @@ fn addr_of() {
                 (&::core::asserting::Wrapper(__local_bind0)).try_capture(&mut __capture0);
                 {
                     ::std::rt::panic_fmt(format_args!("Assertion failed: &elem\nWith captures:\n  elem = {0:?}\n",
-                            __capture0))
+                            __capture0));
                 }
             }
     };
@@ -58,7 +58,7 @@ fn binary() {
                 (&::core::asserting::Wrapper(__local_bind0)).try_capture(&mut __capture0);
                 {
                     ::std::rt::panic_fmt(format_args!("Assertion failed: elem == 1\nWith captures:\n  elem = {0:?}\n",
-                            __capture0))
+                            __capture0));
                 }
             }
     };
@@ -71,7 +71,7 @@ fn binary() {
                 (&::core::asserting::Wrapper(__local_bind0)).try_capture(&mut __capture0);
                 {
                     ::std::rt::panic_fmt(format_args!("Assertion failed: elem >= 1\nWith captures:\n  elem = {0:?}\n",
-                            __capture0))
+                            __capture0));
                 }
             }
     };
@@ -84,7 +84,7 @@ fn binary() {
                 (&::core::asserting::Wrapper(__local_bind0)).try_capture(&mut __capture0);
                 {
                     ::std::rt::panic_fmt(format_args!("Assertion failed: elem > 0\nWith captures:\n  elem = {0:?}\n",
-                            __capture0))
+                            __capture0));
                 }
             }
     };
@@ -97,7 +97,7 @@ fn binary() {
                 (&::core::asserting::Wrapper(__local_bind0)).try_capture(&mut __capture0);
                 {
                     ::std::rt::panic_fmt(format_args!("Assertion failed: elem < 3\nWith captures:\n  elem = {0:?}\n",
-                            __capture0))
+                            __capture0));
                 }
             }
     };
@@ -110,7 +110,7 @@ fn binary() {
                 (&::core::asserting::Wrapper(__local_bind0)).try_capture(&mut __capture0);
                 {
                     ::std::rt::panic_fmt(format_args!("Assertion failed: elem <= 3\nWith captures:\n  elem = {0:?}\n",
-                            __capture0))
+                            __capture0));
                 }
             }
     };
@@ -123,7 +123,7 @@ fn binary() {
                 (&::core::asserting::Wrapper(__local_bind0)).try_capture(&mut __capture0);
                 {
                     ::std::rt::panic_fmt(format_args!("Assertion failed: elem != 3\nWith captures:\n  elem = {0:?}\n",
-                            __capture0))
+                            __capture0));
                 }
             }
     };
@@ -139,7 +139,7 @@ fn unary() {
                 (&::core::asserting::Wrapper(__local_bind0)).try_capture(&mut __capture0);
                 {
                     ::std::rt::panic_fmt(format_args!("Assertion failed: *elem\nWith captures:\n  elem = {0:?}\n",
-                            __capture0))
+                            __capture0));
                 }
             }
     };