Add an UNUSED_SHOWN_NAMES hint to the analyzer

pkg/analyzer/test/generated/hint_code_test.dart

Index: pkg/analyzer/test/generated/hint_code_test.dart
diff --git a/pkg/analyzer/test/generated/hint_code_test.dart b/pkg/analyzer/test/generated/hint_code_test.dart
index fa3da216fadc4f776d7becfc8124e281c4ad2bae..783300a34f91e86461b576e21ef223e6e6e933df 100644
--- a/pkg/analyzer/test/generated/hint_code_test.dart
+++ b/pkg/analyzer/test/generated/hint_code_test.dart
@@ -2838,6 +2838,60 @@ class B {}''');
     verify([source, source2]);
   }
 
+  void test_unusedShownName() {
+    Source source = addSource(r'''
+library L;
+import 'lib1.dart' show A, B;
+A a;''');
+    Source source2 = addNamedSource(
+        "/lib1.dart", r'''
+library lib1;
+class A {}
+class B {}''');
+    computeLibrarySourceErrors(source);
+    assertErrors(source, [HintCode.UNUSED_SHOWN_NAME]);
+    assertNoErrors(source2);
+    verify([source, source2]);
+  }
+
+  void test_unusedShownName_as() {
+    Source source = addSource(r'''
+library L;
+import 'lib1.dart' as p show A, B;
+p.A a;''');
+    Source source2 = addNamedSource(
+        "/lib1.dart", r'''
+library lib1;
+class A {}
+class B {}''');
+    computeLibrarySourceErrors(source);
+    assertErrors(source, [HintCode.UNUSED_SHOWN_NAME]);
+    assertNoErrors(source2);
+    verify([source, source2]);
+  }
+
+  void test_unusedShownName_duplicates() {
+    Source source = addSource(r'''
+library L;
+import 'lib1.dart' show A, B;
+import 'lib1.dart' show C, D;
+A a;
+C c;''');
+    Source source2 = addNamedSource(
+        "/lib1.dart", r'''
+library lib1;
+class A {}
+class B {}
+class C {}
+class D {}''');
+    computeLibrarySourceErrors(source);
+    assertErrors(source, [
+        HintCode.UNUSED_SHOWN_NAME,
+        HintCode.UNUSED_SHOWN_NAME]);
+    assertNoErrors(source2);
+    verify([source, source2]);
+  }
+
   void test_unusedLocalVariable_inCatch_exception() {
     enableUnusedLocalVariable = true;
     Source source = addSource(r'''