Fix prefer_iterable_wheretype in analyzer.

R=brianwilkerson@google.com

Change-Id: Id683ec62a7bdfddb5b2662afbcf57d884767a736
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/127454
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

Author: scheglov

pkg/analyzer/analysis_options.yaml

@@ -10,7 +10,6 @@ analyzer:
     # Ignoring "style" lint rules from pedantic for now. There are pre-existing
     # violations that need to be cleaned up. Each one can be cleaned up and
     # enabled according to the value provided.
-    prefer_iterable_wheretype: ignore
     # TODO(srawlins): At the time of writing, 2600 violations in lib/. The fix
     # is mechanical, via `dartfmt --fix-doc-comments`, but not worth the churn
     # today.

pkg/analyzer/lib/src/dart/resolver/scope.dart

@@ -454,9 +454,10 @@ class LibraryImportScope extends Scope {
   @override
   bool shouldIgnoreUndefined(Identifier node) {
     Iterable<NamespaceCombinator> getShowCombinators(
-            ImportElement importElement) =>
-        importElement.combinators.where((NamespaceCombinator combinator) =>
-            combinator is ShowElementCombinator);
+        ImportElement importElement) {
+      return importElement.combinators.whereType<ShowElementCombinator>();
+    }
+
     if (node is PrefixedIdentifier) {
       String prefix = node.prefix.name;
       String name = node.identifier.name;

pkg/analyzer/lib/src/workspace/gn.dart

@@ -252,8 +252,7 @@ class GnWorkspace extends Workspace {
     }
     return genDir
         .getChildren()
-        .where((resource) => resource is File)
-        .map((resource) => resource as File)
+        .whereType<File>()
         .where((File file) => pathContext.extension(file.path) == '.packages')
         .map((File file) => file.path)
         .toList();
@@ -285,11 +284,7 @@ class GnWorkspace extends Workspace {
     if (!outDirectory.exists) {
       return null;
     }
-    return outDirectory
-        .getChildren()
-        .where((resource) => resource is Folder)
-        .map((resource) => resource as Folder)
-        .firstWhere((Folder folder) {
+    return outDirectory.getChildren().whereType<Folder>().firstWhere((folder) {
       String baseName = pathContext.basename(folder.path);
       // Taking a best guess to identify a build dir. This is clearly a fallback
       // to the config-based method.

pkg/analyzer/test/utils.dart

@@ -16,8 +16,7 @@ import 'package:test/test.dart';
  */
 FunctionElement findLocalFunction(CompilationUnit unit, String name) {
   List<Element> elements = findElementsByName(unit, name);
-  List<Element> functions =
-      elements.where((e) => e is FunctionElement).toList();
+  List<Element> functions = elements.whereType<FunctionElement>().toList();
   expect(functions, hasLength(1));
   return functions[0];
 }
@@ -29,7 +28,7 @@ FunctionElement findLocalFunction(CompilationUnit unit, String name) {
 LocalVariableElement findLocalVariable(CompilationUnit unit, String name) {
   List<Element> elements = findElementsByName(unit, name);
   List<Element> localVariables =
-      elements.where((e) => e is LocalVariableElement).toList();
+      elements.whereType<LocalVariableElement>().toList();
   expect(localVariables, hasLength(1));
   return localVariables[0];
 }