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

Author: dtolnay

Diff for: compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -2460,7 +2460,11 @@ 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,
@@ -2481,7 +2485,9 @@ impl<'a> State<'a> {
                     }
                     self.word("..");
                 }
-                self.space();
+                if !empty {
+                    self.space();
+                }
                 self.word("}");
             }
             PatKind::Tuple(ref elts) => {

Diff for: 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("..");
                 }
-                self.space();
+                if !empty {
+                    self.space();
+                }
                 self.word("}");
             }
             PatKind::Or(ref pats) => {

Diff for: src/test/ui/macros/stringify.rs

@@ -661,9 +661,9 @@ 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::<u8> {}), "Struct::<u8> {  }");
-    assert_eq!(stringify_pat!(Struct::<'static> {}), "Struct::<'static> {  }");
+    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 }");
     assert_eq!(stringify_pat!(Struct { x: _x }), "Struct { x: _x }");
     assert_eq!(stringify_pat!(Struct { .. }), "Struct { .. }");
@@ -672,7 +672,7 @@ fn test_pat() {
     #[rustfmt::skip] // https://github.com/rust-lang/rustfmt/issues/5151
     assert_eq!(
         stringify_pat!(<Struct as Trait>::Type {}),
-        "<Struct as Trait>::Type {  }",
+        "<Struct as Trait>::Type {}",
     );
 
     // PatKind::TupleStruct