Format core and std macro rules, removing needless surrounding blocks

[dtolnay]

Many of the asserting and printing macros in core and std are written with prehistoric-looking formatting, like this:

rust/library/std/src/macros.rs

Lines 96 to 101 in 335ffbf

	macro_rules! println {
	() => ($crate::print!("\n"));
	($($arg:tt)*) => ({
	$crate::io::_print($crate::format_args_nl!($($arg)*));
	})
	}

In modern Rust style this would conventionally be written as follows instead, always using braces and a trailing semicolon on the macro arms:

rust/library/std/src/macros.rs

Lines 98 to 105 in af53809

	macro_rules! println {
	() => {
	$crate::print!("\n")
	};
	($($arg:tt)*) => {
	$crate::io::_print($crate::format_args_nl!($($arg)*))
	};
	}

Getting rid of the unneeded braces inside the expansion reduces extraneous indentation in macro-expanded code. For example:

println!("repro {}", true);

// before:

{
    ::std::io::_print(
        ::core::fmt::Arguments::new_v1(
            &["repro ", "\n"],
            &[::core::fmt::ArgumentV1::new_display(&true)],
        ),
    );
};

// after:

::std::io::_print(
    ::core::fmt::Arguments::new_v1(
        &["repro ", "\n"],
        &[::core::fmt::ArgumentV1::new_display(&true)],
    ),
);

[rust-highfive]

r? @yaahc

(rust-highfive has picked a reviewer for you, use r? to override)

[dtolnay]

This now avoids #94866

[Dylan-DPC]

r? @Dylan-DPC

[Dylan-DPC]

@bors r+ rollup

[bors]

📌 Commit af53809 has been approved by Dylan-DPC

[bors]

⌛ Testing commit af53809 with merge 28838f68c28e8f45725d715555a73c55dbd9323d...

[bors]

💔 Test failed - checks-actions

[dtolnay]

I don't know how to reproduce the run-make-fulldeps/coverage-reports failure on aarch64-gnu, but I noticed this snippet in the logs which looks relevant, so I will try to make the change that it shows.

--- expected_show_coverage.closure.txt	2022-03-13 10:25:55.192734369 +0000
+++ /checkout/obj/build/aarch64-unknown-linux-gnu/test/run-make-fulldeps/coverage-reports/coverage-reports/actual_show_coverage.closure.txt	2022-03-13 11:10:50.435023772 +0000
@@ -116,8 +116,8 @@
   116|      1|
   117|      1|    let
   118|      1|        _unused_closure
-  119|       |    =
-  120|       |        |
+  119|      1|    =
+  120|      1|        |
   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|       |        | _unused_arg: u8 |
+  172|      1|        | _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|      1|        | _unused_arg: u8 |
+  190|       |        | _unused_arg: u8 |
   191|      1|            println!(
   192|      1|                "not called: {}",
   193|      1|                if is_true { "check" } else { "me" }

[dtolnay]

@bors r=Dylan-DPC

[bors]

📌 Commit ac5c657 has been approved by Dylan-DPC