Migration: add support for Angular's @ViewChild() and @ContentChild() annotations.

Bug: https://github.com/dart-lang/sdk/issues/45661
Change-Id: Ie77d720677fb032585e17fe13358afe597e702bd
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/209820
Reviewed-by: Samuel Rawlins <srawlins@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>

pkg/nnbd_migration/lib/instrumentation.dart

@@ -240,6 +240,7 @@ abstract class EdgeOriginInfo {
 enum EdgeOriginKind {
   alreadyMigratedType,
   alwaysNullableType,
+  angularAnnotation,
   argumentErrorCheckNotNull,
   callTearOff,
   compoundAssignment,
@@ -272,7 +273,6 @@ enum EdgeOriginKind {
   nonNullableUsage,
   nonNullAssertion,
   nullabilityComment,
-  optionalAnnotation,
   optionalFormalParameter,
   parameterInheritance,
   quiverCheckNotNull,

pkg/nnbd_migration/lib/src/edge_origin.dart

@@ -64,6 +64,19 @@ class AlwaysNullableTypeOrigin extends EdgeOrigin {
   EdgeOriginKind get kind => EdgeOriginKind.alwaysNullableType;
 }
 
+/// Edge origin resulting from the presence of an Angular annotation such as
+/// `@Optional()`, `@ViewChild(...)`, or `@ContentChild(...)`.
+class AngularAnnotationOrigin extends EdgeOrigin {
+  AngularAnnotationOrigin(Source? source, AstNode node) : super(source, node);
+
+  @override
+  String get description =>
+      "annotated with an Angular annotation indicating nullability";
+
+  @override
+  EdgeOriginKind get kind => EdgeOriginKind.angularAnnotation;
+}
+
 /// Edge origin resulting from the presence of a call to
 /// `ArgumentError.checkNotNull`.
 ///
@@ -542,18 +555,6 @@ class NullabilityCommentOrigin extends EdgeOrigin {
   EdgeOriginKind get kind => EdgeOriginKind.nullabilityComment;
 }
 
-/// Edge origin resulting from the presence of an Angular `@Optional()`
-/// annotation.
-class OptionalAnnotationOrigin extends EdgeOrigin {
-  OptionalAnnotationOrigin(Source? source, AstNode node) : super(source, node);
-
-  @override
-  String get description => "annotated with Angular's @Optional() annotation";
-
-  @override
-  EdgeOriginKind get kind => EdgeOriginKind.optionalAnnotation;
-}
-
 /// Edge origin resulting from the presence of an optional formal parameter.
 ///
 /// For example, in the following code snippet:

pkg/nnbd_migration/lib/src/node_builder.dart

@@ -465,9 +465,13 @@ class NodeBuilder extends GeneralizingAstVisitor<DecoratedType>
         _variables!.recordDecoratedElementType(
             declaredElement.variable, decoratedType.returnType);
       } else {
-        _variables!.recordDecoratedElementType(
-            declaredElement.variable, decoratedType.positionalParameters![0],
+        var type = decoratedType.positionalParameters![0];
+        _variables!.recordDecoratedElementType(declaredElement.variable, type,
             soft: true);
+        if (_hasAngularChildAnnotation(node.metadata)) {
+          _graph.makeNullable(
+              type!.node!, AngularAnnotationOrigin(source, node));
+        }
       }
     }
     return null;
@@ -668,6 +672,12 @@ class NodeBuilder extends GeneralizingAstVisitor<DecoratedType>
       _variables!.recordDecoratedElementType(declaredElement, type);
       variable.initializer?.accept(this);
     }
+    var parent = node.parent;
+    if (parent is FieldDeclaration) {
+      if (_hasAngularChildAnnotation(parent.metadata)) {
+        _graph.makeNullable(type!.node!, AngularAnnotationOrigin(source, node));
+      }
+    }
     return null;
   }
 
@@ -800,7 +810,7 @@ class NodeBuilder extends GeneralizingAstVisitor<DecoratedType>
           element.enclosingElement.name == 'Optional' &&
           _isAngularUri(element.librarySource.uri)) {
         _graph.makeNullable(
-            decoratedType!.node!, OptionalAnnotationOrigin(source, node));
+            decoratedType!.node!, AngularAnnotationOrigin(source, node));
       }
     }
     if (declaredElement.isNamed) {
@@ -893,6 +903,23 @@ class NodeBuilder extends GeneralizingAstVisitor<DecoratedType>
         .recordDecoratedDirectSupertypes(declaredElement, decoratedSupertypes);
   }
 
+  /// Determines if the given [metadata] contains a reference to one of the
+  /// Angular annotations `ViewChild` or `ContentChild`, either of which implies
+  /// nullability of the underlying property.
+  bool _hasAngularChildAnnotation(NodeList<Annotation> metadata) {
+    for (var annotation in metadata) {
+      var element = annotation.element;
+      if (element is ConstructorElement) {
+        var name = element.enclosingElement.name;
+        if ((name == 'ViewChild' || name == 'ContentChild') &&
+            _isAngularUri(element.librarySource.uri)) {
+          return true;
+        }
+      }
+    }
+    return false;
+  }
+
   /// Determines whether the given [uri] comes from the Angular package.
   bool _isAngularUri(Uri uri) {
     if (uri.scheme != 'package') return false;

pkg/nnbd_migration/test/abstract_context.dart

@@ -55,9 +55,15 @@ class AbstractContextTest with ResourceProviderMixin {
     addPackageFile(
         internalUris ? 'third_party.dart_src.angular.angular' : 'angular',
         'angular.dart', '''
+class ContentChild {
+  const ContentChild(Object selector, {Object? read});
+}
 class Optional {
   const Optional();
 }
+class ViewChild {
+  const ViewChild(Object selector, {Object? read});
+}
 ''');
     if (internalUris) {
       addPackageFile('angular', 'angular.dart', '''

pkg/nnbd_migration/test/api_test.dart

@@ -356,6 +356,37 @@ g() {
     await _checkSingleFileChanges(content, expected);
   }
 
+  Future<void> test_angular_contentChild_field() async {
+    addAngularPackage();
+    var content = '''
+import 'dart:html';
+import 'package:angular/angular.dart';
+
+class MyComponent {
+  // Initialize this.bar in the constructor just so the migration tool doesn't
+  // decide to make it nullable due to the lack of initializer.
+  MyComponent(this.bar);
+
+  @ContentChild('foo')
+  Element bar;
+}
+''';
+    var expected = '''
+import 'dart:html';
+import 'package:angular/angular.dart';
+
+class MyComponent {
+  // Initialize this.bar in the constructor just so the migration tool doesn't
+  // decide to make it nullable due to the lack of initializer.
+  MyComponent(this.bar);
+
+  @ContentChild('foo')
+  Element? bar;
+}
+''';
+    await _checkSingleFileChanges(content, expected);
+  }
+
   Future<void> test_angular_optional_constructor_param() async {
     addAngularPackage();
     var content = '''
@@ -415,6 +446,91 @@ class MyComponent {
     await _checkSingleFileChanges(content, expected);
   }
 
+  Future<void> test_angular_viewChild_field() async {
+    addAngularPackage();
+    var content = '''
+import 'dart:html';
+import 'package:angular/angular.dart';
+
+class MyComponent {
+  // Initialize this.bar in the constructor just so the migration tool doesn't
+  // decide to make it nullable due to the lack of initializer.
+  MyComponent(this.bar);
+
+  @ViewChild('foo')
+  Element bar;
+}
+''';
+    var expected = '''
+import 'dart:html';
+import 'package:angular/angular.dart';
+
+class MyComponent {
+  // Initialize this.bar in the constructor just so the migration tool doesn't
+  // decide to make it nullable due to the lack of initializer.
+  MyComponent(this.bar);
+
+  @ViewChild('foo')
+  Element? bar;
+}
+''';
+    await _checkSingleFileChanges(content, expected);
+  }
+
+  Future<void> test_angular_viewChild_field_internal() async {
+    addAngularPackage(internalUris: true);
+    var content = '''
+import 'dart:html';
+import 'package:angular/angular.dart';
+
+class MyComponent {
+  // Initialize this.bar in the constructor just so the migration tool doesn't
+  // decide to make it nullable due to the lack of initializer.
+  MyComponent(this.bar);
+
+  @ViewChild('foo')
+  Element bar;
+}
+''';
+    var expected = '''
+import 'dart:html';
+import 'package:angular/angular.dart';
+
+class MyComponent {
+  // Initialize this.bar in the constructor just so the migration tool doesn't
+  // decide to make it nullable due to the lack of initializer.
+  MyComponent(this.bar);
+
+  @ViewChild('foo')
+  Element? bar;
+}
+''';
+    await _checkSingleFileChanges(content, expected);
+  }
+
+  Future<void> test_angular_viewChild_setter() async {
+    addAngularPackage();
+    var content = '''
+import 'dart:html';
+import 'package:angular/angular.dart';
+
+class MyComponent {
+  @ViewChild('foo')
+  set bar(Element element) {}
+}
+''';
+    var expected = '''
+import 'dart:html';
+import 'package:angular/angular.dart';
+
+class MyComponent {
+  @ViewChild('foo')
+  set bar(Element? element) {}
+}
+''';
+    await _checkSingleFileChanges(content, expected);
+  }
+
   Future<void> test_argumentError_checkNotNull_implies_non_null_intent() async {
     var content = '''
 void f(int i) {