Rollup merge of #91437 - dtolnay:emptybrace, r=nagisa

Pretty print empty blocks as {}

**Example:**

```rust
macro_rules! p {
    ($e:expr) => {
        println!("{}", stringify!($e));
    };
    ($i:item) => {
        println!("{}", stringify!($i));
    };
}

fn main() {
    p!(if true {});
    p!(struct S {});
}
```

**Before:**

```console
if true { }
struct S {
}
```

**After:**

```console
if true {}
struct S {}
```

This affects [`dbg!`](https://doc.rust-lang.org/std/macro.dbg.html), as well as ecosystem uses of stringify such as in [`anyhow::ensure!`](https://docs.rs/anyhow/1/anyhow/macro.ensure.html). Printing a `{ }` in today's heavily rustfmt'd world comes out looking jarring/sloppy.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/test/ui/const-generics/defaults/pretty-printing-ast.stdout b/src/test/ui/const-generics/defaults/pretty-printing-ast.stdout
index 1bceb8cbb94..9f65b8f25ba 100644
--- a/src/test/ui/const-generics/defaults/pretty-printing-ast.stdout
+++ b/src/test/ui/const-generics/defaults/pretty-printing-ast.stdout
@@ -11,9 +11,9 @@ use ::std::prelude::rust_2015::*;
 #[macro_use]
 extern crate std;
 
-trait Foo<const KIND : bool = true> { }
+trait Foo<const KIND : bool = true> {}
 
-fn foo<const SIZE : usize = 5>() { }
+fn foo<const SIZE : usize = 5>() {}
 
 struct Range<const FROM : usize = 0, const LEN : usize = 0, const TO : usize =
              FROM>;