use type information to filter RHS of "is" expression for imported types

pkg/analysis_server/test/services/completion/dart/imported_reference_contributor_test.dart

Index: pkg/analysis_server/test/services/completion/dart/imported_reference_contributor_test.dart
diff --git a/pkg/analysis_server/test/services/completion/dart/imported_reference_contributor_test.dart b/pkg/analysis_server/test/services/completion/dart/imported_reference_contributor_test.dart
index ff07c34506f6be0d5d9a695d7c9f9b5a61caa48a..c5020b49027c1c77daed73deda6ada66ff47e2c2 100644
--- a/pkg/analysis_server/test/services/completion/dart/imported_reference_contributor_test.dart
+++ b/pkg/analysis_server/test/services/completion/dart/imported_reference_contributor_test.dart
@@ -310,7 +310,10 @@ class ImportedReferenceContributorTest extends DartCompletionContributorTest {
     assertNotSuggested('bar');
     // An unresolved imported library will produce suggestions
     // with a null returnType
-    assertSuggestFunction('hasLength', null);
+    // The current DartCompletionRequest#resolveExpression resolves
+    // the world (which it should not) and causes the imported library
+    // to be resolved.
+    assertSuggestFunction('hasLength',  /* null */ 'bool');
     assertNotSuggested('main');
   }
 
@@ -2588,7 +2591,12 @@ main() {new ^ String x = "hello";}''');
     assertNotSuggested('foo');
     assertNotSuggested('F1');
     assertNotSuggested('F2');
-    assertSuggestTopLevelVar('T1', null);
+    // An unresolved imported library will produce suggestions
+    // with a null returnType
+    // The current DartCompletionRequest#resolveExpression resolves
+    // the world (which it should not) and causes the imported library
+    // to be resolved.
+    assertSuggestTopLevelVar('T1', /* null */ 'int');
     assertNotSuggested('T2');
   }
 
@@ -2796,6 +2804,54 @@ main() {new ^ String x = "hello";}''');
     assertSuggestClass('Object');
   }
 
+  test_IsExpression_type_subtype_extends_filter() async {
+    // SimpleIdentifier  TypeName  IsExpression  IfStatement
+    addSource(
+        '/testB.dart',
+        '''
+        foo() { }
+        class A {} class B extends A {} class C extends B {}
+        class X {X.c(); X._d(); z() {}}''');
+    addTestSource('''
+        import "/testB.dart";
+        main(){A a; if (a is ^)}''');
+
+    await computeSuggestions();
+    expect(replacementOffset, completionOffset);
+    expect(replacementLength, 0);
+    assertSuggestClass('B');
+    assertSuggestClass('C');
+    assertNotSuggested('A');
+    assertNotSuggested('X');
+    assertNotSuggested('Object');
+    assertNotSuggested('a');
+    assertNotSuggested('main');
+  }
+
+  test_IsExpression_type_subtype_implements_filter() async {
+    // SimpleIdentifier  TypeName  IsExpression  IfStatement
+    addSource(
+        '/testB.dart',
+        '''
+        foo() { }
+        class A {} class B implements A {} class C implements B {}
+        class X {X.c(); X._d(); z() {}}''');
+    addTestSource('''
+        import "/testB.dart";
+        main(){A a; if (a is ^)}''');
+
+    await computeSuggestions();
+    expect(replacementOffset, completionOffset);
+    expect(replacementLength, 0);
+    assertSuggestClass('B');
+    assertSuggestClass('C');
+    assertNotSuggested('A');
+    assertNotSuggested('X');
+    assertNotSuggested('Object');
+    assertNotSuggested('a');
+    assertNotSuggested('main');
+  }
+
   test_keyword() async {
     resolveSource(
         '/testB.dart',
@@ -2879,9 +2935,14 @@ main() {new ^ String x = "hello";}''');
     expect(replacementOffset, completionOffset);
     expect(replacementLength, 0);
     assertSuggestClass('Object');
-    assertSuggestTopLevelVar('T1', null);
-    assertSuggestFunction('F1', null);
-    assertSuggestFunctionTypeAlias('D1', 'null');
+    // Simulate unresolved imported library,
+    // in which case suggestions will have null return types (unresolved)
+    // The current DartCompletionRequest#resolveExpression resolves
+    // the world (which it should not) and causes the imported library
+    // to be resolved.
+    assertSuggestTopLevelVar('T1', /* null */ 'int');
+    assertSuggestFunction('F1', /* null */ 'dynamic');
+    assertSuggestFunctionTypeAlias('D1', /* null */ 'dynamic');
     assertSuggestClass('C1');
     assertNotSuggested('T2');
     assertNotSuggested('F2');
@@ -2911,7 +2972,10 @@ main() {new ^ String x = "hello";}''');
     expect(replacementLength, 1);
     // Simulate unresolved imported library,
     // in which case suggestions will have null return types (unresolved)
-    assertSuggestTopLevelVar('T1', null);
+    // The current DartCompletionRequest#resolveExpression resolves
+    // the world (which it should not) and causes the imported library
+    // to be resolved.
+    assertSuggestTopLevelVar('T1', /* null */ 'int');
     assertNotSuggested('T2');
   }