[analysis_server] Add helper functions to support flags enums

In the new interactive forms, some of the enums can be combined (eg. `FileExistence.New | FileExisting.Existing`). This adds a flag that produces some helper functions for `hasFlag()` and `combine()`.

These helpers are not used outside of tests in this CL but will be used in a future CL (which I'm trying to avoid getting too big to simplify reviewing).

Change-Id: I1b5f06f05d96781c4bc6a246a0a9309a786c1987
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/505320
Reviewed-by: Keerti Parthasarathy <keertip@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Keerti Parthasarathy <keertip@google.com>

pkg/analysis_server/test/tool/lsp_spec/dart_test.dart

@@ -15,6 +15,30 @@ void main() {
 
 ast.ArrayType _array(String name) => ast.ArrayType(_simple(name));
 
+/// Helper to create a constant with defaults.
+ast.Constant _constant(Object value, {String name = 'x', String? type}) {
+  return ast.Constant(
+    name: name,
+    type: type != null ? ast.TypeReference(type) : ast.TypeReference.lspAny,
+    value: value.toString(),
+  );
+}
+
+/// Helper to create a enum with defaults.
+ast.LspEnum _enum({
+  String name = 'x',
+  String type = 'int',
+  bool flags = false,
+  required List<ast.Member> members,
+}) {
+  return ast.LspEnum(
+    name: name,
+    typeOfValues: ast.TypeReference(type),
+    flags: flags,
+    members: members,
+  );
+}
+
 ast.TypeReference _simple(String name) => ast.TypeReference(name);
 
 ast.UnionType _union(List<String> names) =>
@@ -22,6 +46,27 @@ ast.UnionType _union(List<String> names) =>
 
 @reflectiveTest
 class DartTest {
+  void test_flags_requiresPowerOfTwo_double() {
+    expect(
+      () => _enum(flags: true, members: [_constant(1.2)]),
+      throwsA(isA<AssertionError>()),
+    );
+  }
+
+  void test_flags_requiresPowerOfTwo_nonPowerOfTwo() {
+    expect(
+      () => _enum(flags: true, members: [_constant(3)]),
+      throwsA(isA<AssertionError>()),
+    );
+  }
+
+  void test_flags_requiresPowerOfTwo_string() {
+    expect(
+      () => _enum(flags: true, members: [_constant('test')]),
+      throwsA(isA<AssertionError>()),
+    );
+  }
+
   void test_mapping_arrays() {
     expect(_array('string').dartTypeWithTypeArgs, equals('List<String>'));
   }

pkg/analysis_server/test/tool/lsp_spec/generated_classes_test.dart

@@ -119,6 +119,23 @@ class GeneratedClassesTest {
     expect(a.hashCode, equals(b.hashCode));
   }
 
+  void test_generatedClasses_flagsEnum_combined() {
+    var combined = FileExistence.combine([
+      FileExistence.New,
+      FileExistence.Existing,
+    ]);
+
+    expect(combined.toJson(), 3);
+    expect(combined.hasFlag(FileExistence.New), isTrue);
+    expect(combined.hasFlag(FileExistence.Existing), isTrue);
+    expect(combined.hasFlag(FileExistence(64)), isFalse);
+  }
+
+  void test_generatedClasses_flagsEnum_notCombined() {
+    expect(FileExistence.New.hasFlag(FileExistence.New), isTrue);
+    expect(FileExistence.New.hasFlag(FileExistence.Existing), isFalse);
+  }
+
   void test_interactiveForms_deserialize_formFieldsIntoSubclasses() {
     var stringField = FormField.fromJson({
       'type': {'kind': 'string'},

pkg/analysis_server/tool/lsp_spec/codegen_dart.dart

@@ -686,6 +686,22 @@ void _writeEnumClass(IndentableStringBuffer buffer, LspEnum namespace) {
       'static const $memberName = $namespaceName$constructorName($value);',
     );
   });
+  if (namespace.flags) {
+    buffer
+      ..writeln()
+      ..writeIndentedln(
+        'static $namespaceName combine(List<$namespaceName> values) =>',
+      )
+      ..indent()
+      ..writeIndentedln(
+        '$namespaceName$constructorName(values.fold<$dartType>(0, (combinedValue, value) => combinedValue | value._value));',
+      )
+      ..outdent()
+      ..writeln()
+      ..writeIndentedln(
+        'bool hasFlag($namespaceName value) => (_value & value._value) == value._value;',
+      );
+  }
   buffer
     ..writeln()
     ..writeIndentedln('@override $dartType toJson() => _value;')

pkg/analysis_server/tool/lsp_spec/custom/interactive_forms.dart

@@ -136,6 +136,7 @@ final interactiveFormClasses = <LspEntity>[
   LspEnum(
     name: 'FileExistence',
     typeOfValues: TypeReference.int,
+    flags: true,
     members: [
       // Values should be powers of 2 to allow New|Existing.
       Constant(
@@ -159,6 +160,7 @@ final interactiveFormClasses = <LspEntity>[
   LspEnum(
     name: 'FileType',
     typeOfValues: TypeReference.int,
+    flags: true,
     members: [
       // Values should be powers of 2 to allow Regular|Directory.
       Constant(

pkg/analysis_server/tool/lsp_spec/meta_model.dart

@@ -23,6 +23,10 @@ bool isNullType(TypeBase t) =>
 bool isObjectType(TypeBase t) =>
     resolveTypeAlias(t).dartTypeWithTypeArgs == 'Object';
 
+bool _isPowerOfTwo(int x) {
+  return x > 0 && (x & (x - 1)) == 0;
+}
+
 class AbstractGetter extends Member {
   final TypeBase type;
 
@@ -178,14 +182,23 @@ abstract class LspEntity {
 /// An enum parsed from the LSP JSON model.
 class LspEnum extends LspEntity {
   final TypeBase typeOfValues;
+  final bool flags;
   final List<Member> members;
   LspEnum({
     required super.name,
     super.comment,
     super.isProposed,
     required this.typeOfValues,
+    this.flags = false,
     required this.members,
-  }) {
+  }) : assert(
+         !flags ||
+             members
+                 .whereType<Constant>()
+                 .map((member) => int.tryParse(member.value))
+                 .every((value) => value != null && _isPowerOfTwo(value)),
+         'flags enums require all enum values to be int powers of two.',
+       ) {
     members.sortBy((member) => member.name.toLowerCase());
   }
 }

pkg/analysis_server/tool/lsp_spec/meta_model_cleaner.dart

@@ -190,6 +190,7 @@ class LspMetaModelCleaner {
       comment: _cleanComment(namespace.comment),
       isProposed: namespace.isProposed,
       typeOfValues: namespace.typeOfValues,
+      flags: namespace.flags,
       members: namespace.members
           .where(_includeEntityInOutput)
           .map((member) => _cleanMember(namespace.name, member))
@@ -385,6 +386,7 @@ class LspMetaModelCleaner {
         comment: comment,
         isProposed: dest.isProposed,
         typeOfValues: dest.typeOfValues,
+        flags: dest.flags || source.flags,
         members: [...dest.members, ...source.members],
       );
     } else if (source is Interface && dest is Interface) {
@@ -530,6 +532,7 @@ class LspMetaModelCleaner {
           comment: type.comment,
           isProposed: type.isProposed,
           typeOfValues: type.typeOfValues,
+          flags: type.flags,
           members: type.members,
         );
       } else {

third_party/pkg/language_server_protocol/lib/protocol_custom_generated.dart

@@ -2244,6 +2244,8 @@ class FileExistence implements ToJsonable {
   bool operator ==(Object other) =>
       other is FileExistence && other._value == _value;
 
+  bool hasFlag(FileExistence value) => (_value & value._value) == value._value;
+
   @override
   int toJson() => _value;
 
@@ -2251,6 +2253,10 @@ class FileExistence implements ToJsonable {
   String toString() => _value.toString();
 
   static bool canParse(Object? obj, LspJsonReporter reporter) => obj is int;
+
+  static FileExistence combine(List<FileExistence> values) =>
+      FileExistence(values.fold<int>(
+          0, (combinedValue, value) => combinedValue | value._value));
 }
 
 /// FileType represents the expected filesystem resource type.
@@ -2274,6 +2280,8 @@ class FileType implements ToJsonable {
   @override
   bool operator ==(Object other) => other is FileType && other._value == _value;
 
+  bool hasFlag(FileType value) => (_value & value._value) == value._value;
+
   @override
   int toJson() => _value;
 
@@ -2281,6 +2289,9 @@ class FileType implements ToJsonable {
   String toString() => _value.toString();
 
   static bool canParse(Object? obj, LspJsonReporter reporter) => obj is int;
+
+  static FileType combine(List<FileType> values) => FileType(values.fold<int>(
+      0, (combinedValue, value) => combinedValue | value._value));
 }
 
 class FlutterOutline implements ToJsonable {