JS: Format if statements with no else on a single line

lib/src/js/printer.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of js_ast;
 
 
 class JavaScriptPrintingOptions {
   final bool shouldCompressOutput;
   final bool minifyLocalVariables;
   final bool preferSemicolonToNewlineInMinifiedOutput;
+  final bool allowSingleLineIfStatements;
 
   /// True to allow keywords in properties, such as `obj.var` or `obj.function`
   /// Modern JS engines support this.
   final bool allowKeywordsInProperties;
 
   /// Workaround if `this` is not bound in arrow functions.
   final bool arrowFnBindThisWorkaround;
 
   JavaScriptPrintingOptions(
       {this.shouldCompressOutput: false,
        this.minifyLocalVariables: false,
        this.preferSemicolonToNewlineInMinifiedOutput: false,
        this.allowKeywordsInProperties: false,
+       this.allowSingleLineIfStatements: false,
        this.arrowFnBindThisWorkaround: false});
 }
 
 
 /// An environment in which JavaScript printing is done.  Provides emitting of
 /// text and pre- and post-visit callbacks.
 abstract class JavaScriptPrintingContext {
   /// Signals an error.  This should happen only for serious internal errors.
   void error(String message) { throw message; }
 
@@ skipping 29 matching lines @@
   bool inForInit = false;
   bool atStatementBegin = false;
   bool inNewTarget = false;
   bool pendingSemicolon = false;
   bool pendingSpace = false;
 
   // The current indentation level.
   int _indentLevel = 0;
   // A cache of all indentation strings used so far.
   List<String> _indentList = <String>[""];
+  /// Whether the next call to [indent] should just be a no-op.
+  bool _skipNextIndent = false;
 
   static final identifierCharacterRegExp = new RegExp(r'^[a-zA-Z_0-9$]');
   static final expressionContinuationRegExp = new RegExp(r'^[-+([]');
 
   Printer(JavaScriptPrintingOptions options,
           JavaScriptPrintingContext context,
           {LocalNamer localNamer})
       : options = options,
         context = context,
         shouldCompressOutput = options.shouldCompressOutput,
@@ skipping 90 matching lines @@
     if (shouldCompressOutput) {
       pendingSemicolon = true;
     } else {
       out(";");
       forceLine();
     }
   }
 
   void outIndent(String str) { indent(); out(str); }
   void outIndentLn(String str) { indent(); outLn(str); }
+
+  void skipNextIndent() {
+    _skipNextIndent = true;
+  }
+
   void indent() {
+    if (_skipNextIndent) {
+      _skipNextIndent = false;
+      return;
+    }
     if (!shouldCompressOutput) {
       out(indentation);
     }
   }
 
   visit(Node node) {
     context.enterNode(node);
     node.accept(this);
     context.exitNode(node);
   }
@@ skipping 97 matching lines @@
         then = new Block(<Statement>[then]);
       }
     }
     if (shouldIndent) indent();
     out("if");
     spaceOut();
     out("(");
     visitNestedExpression(node.condition, EXPRESSION,
                           newInForInit: false, newAtStatementBegin: false);
     out(")");
-    bool thenWasBlock =
-        blockBody(then, needsSeparation: false, needsNewline: !hasElse);
+    bool thenWasBlock;
+    if (options.allowSingleLineIfStatements && !hasElse && then is! Block) {
+      thenWasBlock = false;
+      spaceOut();
+      skipNextIndent();
+      visit(then);
+    } else {
+      thenWasBlock =
+          blockBody(then, needsSeparation: false, needsNewline: !hasElse);
+    }
     if (hasElse) {
       if (thenWasBlock) {
         spaceOut();
       } else {
         indent();
       }
       out("else");
       if (elsePart is If) {
         pendingSpace = true;
         ifOut(elsePart, false);
@@ skipping 1294 matching lines @@
     declare(node.name);
     node.function.accept(this);
   }
 
   visitClassExpression(ClassExpression node) {
     declare(node.name);
     if (node.heritage != null) node.heritage.accept(this);
     for (Method element in node.methods) element.accept(this);
   }
 }