Delegating AST Visitor and Linter refactoring.

pkg/analyzer/test/generated/engine_test.dart

Index: pkg/analyzer/test/generated/engine_test.dart
===================================================================
--- pkg/analyzer/test/generated/engine_test.dart	(revision 42890)
+++ pkg/analyzer/test/generated/engine_test.dart	(working copy)
@@ -4090,18 +4090,49 @@
 
     RecordingErrorListener errorListener = new RecordingErrorListener();
 
-    LintGeneratorTest_Verifier verifier = new LintGeneratorTest_Verifier();
+    LintGeneratorTest_Linter linter = new LintGeneratorTest_Linter();
 
     LintGenerator lintGenerator =
-        new LintGenerator(units, errorListener, [verifier]);
+        new LintGenerator(units, errorListener, [linter]);
     lintGenerator.generate();
 
-    verifier.testExpectations();
+    linter.testExpectations();
   }
+
+  void test_generate_null_visitor() {
+
+    InternalAnalysisContext context = AnalysisContextFactory.contextWithCore();
+    ChangeSet changeSet = new ChangeSet();
+    Source librarySource =
+        new FileBasedSource.con1(FileUtilities2.createFile("/test.dart"));
+    changeSet.addedSource(librarySource);
+    context.applyChanges(changeSet);
+    context.setContents(librarySource, r'''
+library lib;
+''');
+
+    CompilationUnit unit =
+        context.resolveCompilationUnit2(librarySource, librarySource);
+    List<CompilationUnit> units = <CompilationUnit>[];
+    units.add(unit);
+
+    RecordingErrorListener errorListener = new RecordingErrorListener();
+
+    Linter badLinter = new LintGeneratorTest_Linter_Null_Visitor();
+    LintGeneratorTest_Linter goodLinter = new LintGeneratorTest_Linter();
+
+    LintGenerator lintGenerator =
+        new LintGenerator(units, errorListener, [badLinter, goodLinter]);
+    // Test that generate does not fall down with a null visitor
+    lintGenerator.generate();
+    // Well-formed linter should still get called
+    goodLinter.testExpectations();
+  }
+
 }
 
 
-class LintGeneratorTest_Verifier extends LintVerifier {
+class LintGeneratorTest_Linter extends Linter with SimpleAstVisitor<Object> {

[Brian Wilkerson, 2015/01/15 14:59:54]

Note that the original class name was only chosen because in Java the class
Verifier was an inner class. (That's the only time you'll find underscores in
type names.) Up to you whether to change it.

[pquitslund, 2015/01/15 18:07:30]

Thanks.  Were this Java, it would be an inner class so I'll stick with it for
now.

 
   bool visited;
 
@@ -4115,9 +4146,17 @@
     expect(reporter, isNotNull);
     expect(visited, isTrue);
   }
+
+  @override
+  AstVisitor getVisitor() => this;
 }
 
+class LintGeneratorTest_Linter_Null_Visitor extends Linter {
+  @override
+  AstVisitor getVisitor() => null;
+}
 
+
 @reflectiveTest
 class GetContentTaskTest extends EngineTestCase {
   void test_accept() {