Improve empty definitions of contracts and functions

src/printer.js

@@ -54,24 +54,29 @@ function genericPrint(path, options, print) {
         ]);
       }
       return concat(['import ', doc, ';']);
-    case 'ContractDefinition':
-      doc = concat([node.kind, ' ', node.name]);
+    case 'ContractDefinition': {
+      let parts = [node.kind, ' ', node.name];
+
       if (node.baseContracts.length > 0) {
-        doc = concat([
-          doc,
+        parts = parts.concat([
           ' is ',
           join(', ', path.map(print, 'baseContracts'))
         ]);
       }
-      return concat([
-        doc,
-        ' {',
-        indent(line),
-        indent(printPreservingEmptyLines(path, 'subNodes', options, print)),
-        line,
-        '}',
-        line
-      ]);
+
+      parts.push(' {');
+      if (node.subNodes.length > 0) {
+        parts = parts.concat([
+          indent(line),
+          indent(printPreservingEmptyLines(path, 'subNodes', options, print)),
+          line
+        ]);
+      }
+      parts.push('}');
+      parts.push(line);
+
+      return concat(parts);
+    }
     case 'InheritanceSpecifier': {
       let parts = [path.call(print, 'baseName')];
 
@@ -159,6 +164,11 @@ function genericPrint(path, options, print) {
       }
       return doc;
     case 'Block': {
+      // if block is empty, just return the pair of braces
+      if (node.statements.length === 0 && !node.comments) {
+        return '{}';
+      }
+
       const parts = [
         '{',
         indent(line),

tests/AllSolidityFeatures/__snapshots__/jsfmt.spec.js.snap

@@ -466,9 +466,7 @@ contract Base {
 }
 
 contract Derived is Base(0) {
-  function Derived(uint i) Base(i) {
-
-  }
+  function Derived(uint i) Base(i) {}
 }
 
 
@@ -636,19 +634,13 @@ contract DualIndex {
 }
 
 
-contract A {
-
-}
-
-
-contract B {
+contract A {}
 
-}
 
+contract B {}
 
-contract C is A, B {
 
-}
+contract C is A, B {}
 
 
 contract TestPrivate {
@@ -673,9 +665,7 @@ contract FromSolparse is A, B, TestPrivate, TestInternal {
 contract CommentedOutFunction {
   // FYI: This empty function, as well as the commented
   // out function below (bad code) is important to this test.
-  function() {
-
-  }
+  function() {}
 
   // function something()
   //  uint x = 10;
@@ -714,9 +704,7 @@ contract NewStuff {
 
 // modifier with expression
 contract MyContract {
-  function fun() mymodifier(foo.bar()) {
-
-  }
+  function fun() mymodifier(foo.bar()) {}
 }
 
 
@@ -843,9 +831,7 @@ contract Ballot {
     uint[],
     address myAdd,
     string[] names
-  ) {
-
-  }
+  ) {}
   function foobar() payable owner(myPrice) returns (
     uint[],
     address myAdd,