Use AnalysisDriver.getErrors() to get cached errors for already analyzed files.

pkg/analyzer/test/src/dart/analysis/driver_test.dart

 // Copyright (c) 2016, 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.
 
 library analyzer.test.driver;
 
 import 'dart:async';
 import 'dart:convert';
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 676 matching lines @@
 
     driver.priorityFiles = [templatePath];
     driver.changeFile(templatePath);
     await driver.waitForIdle();
     expect(allExceptions, isEmpty);
     expect(allResults, isEmpty);
 
     expect(driver.knownFiles, isNot(contains(templatePath)));
   }
 
+  test_getErrors() async {
+    String content = 'int f() => 42 + bar();';
+    addTestFile(content, priority: true);
+
+    ErrorsResult result = await driver.getErrors(testFile);
+    expect(result.path, testFile);
+    expect(result.uri.toString(), 'package:test/test.dart');
+    expect(result.contentHash, _md5(content));
+    expect(result.errors, hasLength(1));
+  }
+
   test_getFilesReferencingName() async {
     var a = _p('/test/bin/a.dart');
     var b = _p('/test/bin/b.dart');
     var c = _p('/test/bin/c.dart');
     var d = _p('/test/bin/d.dart');
     var e = _p('/test/bin/e.dart');
 
     provider.newFile(a, 'class A {}');
     provider.newFile(b, "import 'a.dart'; A a;");
     provider.newFile(c, "import 'a.dart'; var a = new A();");
@@ skipping 651 matching lines @@
     await driver.getResult(p);
 
     // Update the file.
     provider.newFile(p, 'class A2 {}');
 
     ParseResult parseResult = await driver.parseFile(p);
     var clazz = parseResult.unit.declarations[0] as ClassDeclaration;
     expect(clazz.name.name, 'A2');
   }
 
+  test_part_getErrors_afterLibrary() async {
+    var a = _p('/test/lib/a.dart');
+    var b = _p('/test/lib/b.dart');
+    var c = _p('/test/lib/c.dart');
+    provider.newFile(
+        a,
+        r'''
+library a;
+import 'b.dart';
+part 'c.dart';
+class A {}
+var c = new C();
+''');
+    provider.newFile(b, 'class B {}');
+    provider.newFile(
+        c,
+        r'''
+part of a;
+class C {}
+var a = new A();
+var b = new B();
+''');
+
+    driver.addFile(a);
+    driver.addFile(b);
+    driver.addFile(c);
+
+    // Process a.dart so that we know that it's a library for c.dart later.
+    {
+      ErrorsResult result = await driver.getErrors(a);
+      expect(result.errors, isEmpty);
+    }
+
+    // c.dart does not have errors in the context of a.dart
+    {
+      ErrorsResult result = await driver.getErrors(c);
+      expect(result.errors, isEmpty);
+    }
+  }
+
+  test_part_getErrors_beforeLibrary() async {
+    var a = _p('/test/lib/a.dart');
+    var b = _p('/test/lib/b.dart');
+    var c = _p('/test/lib/c.dart');
+    provider.newFile(
+        a,
+        r'''
+library a;
+import 'b.dart';
+part 'c.dart';
+class A {}
+var c = new C();
+''');
+    provider.newFile(b, 'class B {}');
+    provider.newFile(
+        c,
+        r'''
+part of a;
+class C {}
+var a = new A();
+var b = new B();
+''');
+
+    driver.addFile(a);
+    driver.addFile(b);
+    driver.addFile(c);
+
+    // c.dart is resolve in the context of a.dart, so have no errors
+    {
+      ErrorsResult result = await driver.getErrors(c);
+      expect(result.errors, isEmpty);
+    }
+  }
+
   test_part_getResult_afterLibrary() async {
     var a = _p('/test/lib/a.dart');
     var b = _p('/test/lib/b.dart');
     var c = _p('/test/lib/c.dart');
     provider.newFile(
         a,
         r'''
 library a;
 import 'b.dart';
 part 'c.dart';
@@ skipping 514 matching lines @@
    * Return the [provider] specific path for the given Posix [path].
    */
   String _p(String path) => provider.convertPath(path);
 
   static String _md5(String content) {
     return hex.encode(md5.convert(UTF8.encode(content)).bytes);
   }
 }
 
 class _SourceMock extends TypedMock implements Source {}