Rollup merge of #99689 - dtolnay:write, r=Mark-Simulacrum

Revert `write!` and `writeln!` to late drop temporaries

Closes (on master, but not on beta) #99684 by reverting the `write!` and `writeln!` parts of #96455.

argument position | before<br>#94868 | after<br>#94868 | after<br>#96455 | after<br>this PR | desired<br>(unimplementable)
--- |:---:|:---:|:---:|:---:|:---:
`write!($tmp, "…", …)` | **⸺late** | **⸺late** | *early⸺* | **⸺late** | **⸺late**
`write!(…, "…", $tmp)` | **⸺late** | **⸺late** | *early⸺* | **⸺late** | *early⸺*
`writeln!($tmp, "…", …)` | **⸺late** | **⸺late** | *early⸺* | **⸺late** | **⸺late**
`writeln!(…, "…", $tmp)` | **⸺late** | **⸺late** | *early⸺* | **⸺late** | *early⸺*
`print!("…", $tmp)` | **⸺late** | **⸺late** | *early⸺* | *early⸺* | *early⸺*
`println!("…", $tmp)` | *early⸺* | **⸺late** | *early⸺* | *early⸺* | *early⸺*
`eprint!("…", $tmp)` | **⸺late** | **⸺late** | *early⸺* | *early⸺* | *early⸺*
`eprintln!("…", $tmp)` | *early⸺* | **⸺late**| *early⸺* | *early⸺* | *early⸺*
`panic!("…", $tmp)` | *early⸺* | *early⸺* | *early⸺* | *early⸺* | *early⸺*

"Late drop" refers to dropping temporaries at the nearest semicolon **outside** of the macro invocation.

"Early drop" refers to dropping temporaries inside of the macro invocation.

Author: Dylan-DPC

core/src/macros/mod.rs

@@ -496,10 +496,9 @@ macro_rules! r#try {
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "write_macro")]
 macro_rules! write {
-    ($dst:expr, $($arg:tt)*) => {{
-        let result = $dst.write_fmt($crate::format_args!($($arg)*));
-        result
-    }};
+    ($dst:expr, $($arg:tt)*) => {
+        $dst.write_fmt($crate::format_args!($($arg)*))
+    };
 }
 
 /// Write formatted data into a buffer, with a newline appended.
@@ -554,10 +553,9 @@ macro_rules! writeln {
     ($dst:expr $(,)?) => {
         $crate::write!($dst, "\n")
     };
-    ($dst:expr, $($arg:tt)*) => {{
-        let result = $dst.write_fmt($crate::format_args_nl!($($arg)*));
-        result
-    }};
+    ($dst:expr, $($arg:tt)*) => {
+        $dst.write_fmt($crate::format_args_nl!($($arg)*))
+    };
 }
 
 /// Indicates unreachable code.