Rollup merge of #92418 - dtolnay:emptystructpat, r=michaelwoerister

Fix spacing in pretty printed PatKind::Struct with no fields

Follow-up to #92238 fixing one of the FIXMEs.

```rust
macro_rules! repro {
    ($pat:pat) => {
        stringify!($pat)
    };
}

fn main() {
    println!("{}", repro!(Struct {}));
}
```

Before:&ensp;<code>Struct&nbsp;{&nbsp;&nbsp;}</code>
After:&ensp;<code>Struct&nbsp;{}</code>

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -2461,7 +2461,11 @@ impl<'a> State<'a> {
                     self.print_path(path, true, 0);
                 }
                 self.nbsp();
-                self.word_space("{");
+                self.word("{");
+                let empty = fields.is_empty() && !etc;
+                if !empty {
+                    self.space();
+                }
                 self.commasep_cmnt(
                     Consistent,
                     &fields,
@@ -2482,7 +2486,9 @@ impl<'a> State<'a> {
                     }
                     self.word("..");
                 }
+                if !empty {
                     self.space();
+                }
                 self.word("}");
             }
             PatKind::Tuple(ref elts) => {

compiler/rustc_hir_pretty/src/lib.rs

@@ -1874,7 +1874,11 @@ impl<'a> State<'a> {
             PatKind::Struct(ref qpath, ref fields, etc) => {
                 self.print_qpath(qpath, true);
                 self.nbsp();
-                self.word_space("{");
+                self.word("{");
+                let empty = fields.is_empty() && !etc;
+                if !empty {
+                    self.space();
+                }
                 self.commasep_cmnt(
                     Consistent,
                     &fields,
@@ -1895,7 +1899,9 @@ impl<'a> State<'a> {
                     }
                     self.word("..");
                 }
+                if !empty {
                     self.space();
+                }
                 self.word("}");
             }
             PatKind::Or(ref pats) => {

src/test/ui/macros/stringify.rs

@@ -661,7 +661,7 @@ fn test_pat() {
     assert_eq!(stringify_pat!(ref mut _x @ _), "ref mut _x @ _");
 
     // PatKind::Struct
-    assert_eq!(stringify_pat!(Struct {}), "Struct {  }"); // FIXME
+    assert_eq!(stringify_pat!(Struct {}), "Struct {}");
     assert_eq!(stringify_pat!(Struct::<u8> {}), "Struct::<u8> {}");
     assert_eq!(stringify_pat!(Struct::<'static> {}), "Struct::<'static> {}");
     assert_eq!(stringify_pat!(Struct { x }), "Struct { x }");