Auto merge of #96490 - dtolnay:writetmpbackport, r=Mark-Simulacrum

Make [e]println macros eagerly drop temporaries (for backport)

This PR extracts the subset of #96455 which is only the parts necessary for fixing the 1.61-beta regressions in #96434.

My larger PR #96455 contains a few other changes relative to the pre-#94868 behavior; those are not necessary to backport into 1.61.

argument position | before #94868 | after #94868 | after this PR
--- |:---:|:---:|:---:
`write!($tmp, "…", …)` | :rage: | :rage: | :rage:
`write!(…, "…", $tmp)` | :rage: | :rage: | :rage:
`writeln!($tmp, "…", …)` | :rage: | :rage: | :rage:
`writeln!(…, "…", $tmp)` | :rage: | :rage: | :rage:
`print!("…", $tmp)` | :rage: | :rage: | :rage:
`println!("…", $tmp)` | :smiley_cat: | :rage: | :smiley_cat:
`eprint!("…", $tmp)` | :rage: | :rage: | :rage:
`eprintln!("…", $tmp)` | :smiley_cat: | :rage: | :smiley_cat:
`panic!("…", $tmp)` | :smiley_cat: | :smiley_cat: | :smiley_cat:

Author: bors

library/std/src/macros.rs

@@ -99,9 +99,9 @@ macro_rules! println {
     () => {
         $crate::print!("\n")
     };
-    ($($arg:tt)*) => {
-        $crate::io::_print($crate::format_args_nl!($($arg)*))
-    };
+    ($($arg:tt)*) => {{
+        $crate::io::_print($crate::format_args_nl!($($arg)*));
+    }};
 }
 
 /// Prints to the standard error.
@@ -164,9 +164,9 @@ macro_rules! eprintln {
     () => {
         $crate::eprint!("\n")
     };
-    ($($arg:tt)*) => {
-        $crate::io::_eprint($crate::format_args_nl!($($arg)*))
-    };
+    ($($arg:tt)*) => {{
+        $crate::io::_eprint($crate::format_args_nl!($($arg)*));
+    }};
 }
 
 /// Prints and returns the value of a given expression for quick and dirty

src/test/pretty/dollar-crate.pp

@@ -9,5 +9,5 @@
 // pp-exact:dollar-crate.pp
 
 fn main() {
-    ::std::io::_print(::core::fmt::Arguments::new_v1(&["rust\n"], &[]));
+    { ::std::io::_print(::core::fmt::Arguments::new_v1(&["rust\n"], &[])); };
 }

src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.closure.txt

@@ -116,8 +116,8 @@
   116|      1|
   117|      1|    let
   118|      1|        _unused_closure
-  119|      1|    =
-  120|      1|        |
+  119|       |    =
+  120|       |        |
   121|       |            mut countdown
   122|       |        |
   123|      0|    {
@@ -173,7 +173,7 @@
   169|       |    ;
   170|       |
   171|      1|    let short_used_not_covered_closure_line_break_no_block_embedded_branch =
-  172|      1|        | _unused_arg: u8 |
+  172|       |        | _unused_arg: u8 |
   173|      0|            println!(
   174|      0|                "not called: {}",
   175|      0|                if is_true { "check" } else { "me" }
@@ -191,7 +191,7 @@
   187|       |    ;
   188|       |
   189|      1|    let short_used_covered_closure_line_break_no_block_embedded_branch =
-  190|       |        | _unused_arg: u8 |
+  190|      1|        | _unused_arg: u8 |
   191|      1|            println!(
   192|      1|                "not called: {}",
   193|      1|                if is_true { "check" } else { "me" }

src/test/ui/macros/trace-macro.stderr

@@ -5,5 +5,5 @@ LL |     println!("Hello, World!");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: expanding `println! { "Hello, World!" }`
-   = note: to `$crate :: io :: _print($crate :: format_args_nl! ("Hello, World!"))`
+   = note: to `{ $crate :: io :: _print($crate :: format_args_nl! ("Hello, World!")) ; }`
 

src/test/ui/pattern/usefulness/tuple-struct-nonexhaustive.stderr

@@ -12,7 +12,7 @@ LL | struct Foo(isize, isize);
    = note: the matched value is of type `Foo`
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |
-LL ~         Foo(2, b) => println!("{}", b),
+LL ~         Foo(2, b) => println!("{}", b)
 LL +         Foo(_, _) => todo!()
    |