Print a block when encountering consequents that are if statements

packages/babel-core/test/fixtures/plugins/nested-if-alternate/exec.js

@@ -5,6 +5,7 @@ var res = transform('', {
       visitor: {
         Program: function(path) {
           if (this.done) return;
+          // if (false) { if (true) 42; } else 23;
           var inner = t.ifStatement(t.booleanLiteral(true), t.expressionStatement(t.numericLiteral(42)), null);
           var outer = t.ifStatement(t.booleanLiteral(false), inner, t.expressionStatement(t.numericLiteral(23)));
           path.replaceWith(t.program([outer]));

packages/babel-generator/src/generators/statements.js

@@ -16,8 +16,21 @@ export function IfStatement(node: Object) {
   this.push(")");
   this.space();
 
+  let consequentIsIf = t.isIfStatement(node.consequent);
+  if (consequentIsIf) {
+    this.push("{");
+    this.newline();
+    this.indent();
+  }
+
   this.printAndIndentOnComments(node.consequent, node);
 
+  if (consequentIsIf) {
+    this.dedent();
+    this.newline();
+    this.push("}");
+  }
+
   if (node.alternate) {
     if (this.isLast("}")) this.space();
     this.push("else ");