Add some command line options to debug AST parsing of illegal dart

compiler/java/com/google/dart/compiler/DartCompiler.java

Index: compiler/java/com/google/dart/compiler/DartCompiler.java
diff --git a/compiler/java/com/google/dart/compiler/DartCompiler.java b/compiler/java/com/google/dart/compiler/DartCompiler.java
index aff1a5359b1b90e32ecaad14d362ed50ddd4296f..8a89af73d9d9c6db96d5fa77372938f9f3ff13a1 100644
--- a/compiler/java/com/google/dart/compiler/DartCompiler.java
+++ b/compiler/java/com/google/dart/compiler/DartCompiler.java
@@ -16,6 +16,7 @@ import com.google.dart.compiler.UnitTestBatchRunner.Invocation;
 import com.google.dart.compiler.ast.DartDirective;
 import com.google.dart.compiler.ast.DartLibraryDirective;
 import com.google.dart.compiler.ast.DartNode;
+import com.google.dart.compiler.ast.DartToSourceVisitor;
 import com.google.dart.compiler.ast.DartUnit;
 import com.google.dart.compiler.ast.LibraryNode;
 import com.google.dart.compiler.ast.LibraryUnit;
@@ -41,6 +42,7 @@ import com.google.dart.compiler.resolver.ResolverErrorCode;
 import com.google.dart.compiler.resolver.SupertypeResolver;
 import com.google.dart.compiler.resolver.TopLevelElementBuilder;
 import com.google.dart.compiler.type.TypeAnalyzer;
+import com.google.dart.compiler.util.DefaultTextOutput;
 
 import org.kohsuke.args4j.CmdLineException;
 import org.kohsuke.args4j.CmdLineParser;
@@ -1027,11 +1029,25 @@ public class DartCompiler {
     try {
       File outputDirectory = config.getOutputDirectory();
       DefaultDartArtifactProvider provider = new DefaultDartArtifactProvider(outputDirectory);
-      DefaultDartCompilerListener listener = new DefaultDartCompilerListener(
-          config.printErrorFormat());
-
       // Compile the Dart application and its dependencies.
-      LibrarySource lib = new UrlLibrarySource(sourceFile);
+      final LibrarySource lib = new UrlLibrarySource(sourceFile);
+      DefaultDartCompilerListener listener;
+      if (config.getCompilerOptions().showSourceFromAst()) {
+        listener = new DefaultDartCompilerListener(config.printErrorFormat()) {
+          @Override
+          public void unitCompiled(DartUnit unit) {
+            if (unit.getLibrary() != null) {
+              if (unit.getLibrary().getSource() == lib) {
+                DefaultTextOutput output = new DefaultTextOutput(false);
+                unit.accept(new DartToSourceVisitor(output));
+                System.out.println(output.toString());
+              }
+            }
+          }
+        };
+      } else {
+        listener = new DefaultDartCompilerListener(config.printErrorFormat());
+      }
       String errorString = compileLib(lib, config, provider, listener);
       return errorString;
     } finally {