Format empty structs correctly

src/nodes/StructDefinition.js

@@ -7,17 +7,23 @@ const {
 const { printSeparatedList } = require('../common/printer-helpers');
 
 const StructDefinition = {
-  print: ({ node, path, print }) => [
-    'struct ',
-    node.name,
-    ' {',
-    printSeparatedList(path.map(print, 'members'), {
-      firstSeparator: hardline,
-      separator: [';', hardline],
-      lastSeparator: [';', hardline]
-    }),
-    '}'
-  ]
+  print: ({ node, path, print }) => {
+    const parts = ['struct ', node.name, ' {'];
+
+    if (node.members.length > 0) {
+      parts.push(
+        printSeparatedList(path.map(print, 'members'), {
+          firstSeparator: hardline,
+          separator: [';', hardline],
+          lastSeparator: [';', hardline]
+        })
+      );
+    }
+
+    parts.push('}');
+
+    return parts;
+  }
 };
 
 module.exports = StructDefinition;

tests/format/Issues/Issue799.sol

@@ -0,0 +1 @@
+struct EmptyStruct {}

tests/format/Issues/__snapshots__/jsfmt.spec.js.snap

@@ -170,3 +170,17 @@ contract Issue564 {
 
 ================================================================================
 `;
+
+exports[`Issue799.sol format 1`] = `
+====================================options=====================================
+parsers: ["solidity-parse"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+struct EmptyStruct {}
+
+=====================================output=====================================
+struct EmptyStruct {}
+
+================================================================================
+`;