Unnamed libraries

Fixes https://github.com/dart-lang/language/issues/1073

Spec: https://github.com/dart-lang/language/blob/master/accepted/future-releases/unnamed-libraries/feature-specification.md

This work allows library directives without a name. Every single one would look like this:

```
library;
```

:) it was a little anti-climactic implementing a non-feature like this, but there it is.

The affordance for a library directive without a name is guarded by an experiment flag, `--unnamed-libraries`.

Change-Id: I8612238359e88d6082f7e89d0d0fc624fdb45273
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/257490
Commit-Queue: Samuel Rawlins <srawlins@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Reviewed-by: Kevin Moore <kevmoo@google.com>

pkg/_fe_analyzer_shared/lib/src/parser/forwarding_listener.dart

@@ -973,8 +973,8 @@ class ForwardingListener implements Listener {
   }
 
   @override
-  void endLibraryName(Token libraryKeyword, Token semicolon) {
-    listener?.endLibraryName(libraryKeyword, semicolon);
+  void endLibraryName(Token libraryKeyword, Token semicolon, bool hasName) {
+    listener?.endLibraryName(libraryKeyword, semicolon, hasName);
   }
 
   @override

pkg/_fe_analyzer_shared/lib/src/parser/listener.dart

@@ -968,7 +968,7 @@ class Listener implements UnescapeErrorListener {
   /// Handle the end of a library directive.  Substructures:
   /// - Metadata
   /// - Library name (a qualified identifier)
-  void endLibraryName(Token libraryKeyword, Token semicolon) {
+  void endLibraryName(Token libraryKeyword, Token semicolon, bool hasName) {
     logEvent("LibraryName");
   }
 

pkg/_fe_analyzer_shared/lib/src/parser/parser_impl.dart

@@ -654,17 +654,23 @@ class Parser {
 
   /// ```
   /// libraryDirective:
-  ///   'library' qualified ';'
+  ///   'library' qualified? ';'
   /// ;
   /// ```
   Token parseLibraryName(Token libraryKeyword) {
     assert(optional('library', libraryKeyword));
     listener.beginUncategorizedTopLevelDeclaration(libraryKeyword);
     listener.beginLibraryName(libraryKeyword);
-    Token token = parseQualified(libraryKeyword, IdentifierContext.libraryName,
-        IdentifierContext.libraryNameContinuation);
-    token = ensureSemicolon(token);
-    listener.endLibraryName(libraryKeyword, token);
+    Token token = libraryKeyword.next!;
+    bool hasName = !optional(';', token);
+    if (hasName) {
+      token = parseQualified(libraryKeyword, IdentifierContext.libraryName,
+          IdentifierContext.libraryNameContinuation);
+      token = ensureSemicolon(token);
+    } else {
+      token = ensureSemicolon(libraryKeyword);
+    }
+    listener.endLibraryName(libraryKeyword, token, hasName);
     return token;
   }
 

pkg/analysis_server/lib/src/operation/operation_analysis.dart

@@ -130,7 +130,7 @@ void sendAnalysisNotificationOverrides(
 String? _computeLibraryName(CompilationUnit unit) {
   for (var directive in unit.directives) {
     if (directive is LibraryDirective) {
-      return directive.name.name;
+      return directive.name2?.name;
     }
   }
   for (var directive in unit.directives) {

pkg/analysis_server/lib/src/services/kythe/kythe_visitors.dart

@@ -432,12 +432,9 @@ class KytheDartVisitor extends GeneralizingAstVisitor<void> with OutputUtils {
           }
         }
 
-        var start = 0;
-        var end = 0;
-        if (libraryDirective != null) {
-          start = libraryDirective.name.offset;
-          end = libraryDirective.name.end;
-        }
+        final libraryName = libraryDirective?.name2;
+        final start = libraryName?.offset ?? 0;
+        final end = libraryName?.end ?? 0;
 
         // package node
         var packageVName = addNodeAndFacts(schema.PACKAGE_KIND,

pkg/analysis_server/tool/code_completion/code_metrics.dart

@@ -871,7 +871,7 @@ class CodeShapeDataCollector extends RecursiveAstVisitor<void> {
     _visitChildren(node, {
       'documentationComment': node.documentationComment,
       'metadata': node.metadata,
-      'name': node.name,
+      'name': node.name2,
     });
     super.visitLibraryDirective(node);
   }

pkg/analyzer/lib/dart/analysis/features.dart

@@ -66,6 +66,9 @@ abstract class Feature {
   static final nonfunction_type_aliases =
       ExperimentalFeatures.nonfunction_type_aliases;
 
+  /// Feature information for unnamed libraries.
+  static final unnamedLibraries = ExperimentalFeatures.unnamed_libraries;
+
   /// Feature information for variance.
   static final variance = ExperimentalFeatures.variance;
 

pkg/analyzer/lib/dart/ast/ast.dart

@@ -3334,7 +3334,7 @@ abstract class LibraryAugmentationDirective implements UriBasedDirective {
 /// A library directive.
 ///
 ///    libraryDirective ::=
-///        [Annotation] 'library' [Identifier] ';'
+///        [Annotation] 'library' [LibraryIdentifier]? ';'
 ///
 /// Clients may not extend, implement or mix-in this class.
 abstract class LibraryDirective implements Directive {
@@ -3342,8 +3342,12 @@ abstract class LibraryDirective implements Directive {
   Token get libraryKeyword;
 
   /// Return the name of the library being defined.
+  @Deprecated('Use name2')
   LibraryIdentifier get name;
 
+  /// Return the name of the library being defined.
+  LibraryIdentifier? get name2;
+
   /// Return the semicolon terminating the directive.
   Token get semicolon;
 }

pkg/analyzer/lib/src/dart/analysis/experiments.g.dart

@@ -40,6 +40,7 @@ final _knownFeatures = <String, ExperimentalFeature>{
   EnableString.super_parameters: ExperimentalFeatures.super_parameters,
   EnableString.test_experiment: ExperimentalFeatures.test_experiment,
   EnableString.triple_shift: ExperimentalFeatures.triple_shift,
+  EnableString.unnamed_libraries: ExperimentalFeatures.unnamed_libraries,
   EnableString.value_class: ExperimentalFeatures.value_class,
   EnableString.variance: ExperimentalFeatures.variance,
 };
@@ -110,6 +111,9 @@ class EnableString {
   /// String to enable the experiment "triple-shift"
   static const String triple_shift = 'triple-shift';
 
+  /// String to enable the experiment "unnamed-libraries"
+  static const String unnamed_libraries = 'unnamed-libraries';
+
   /// String to enable the experiment "value-class"
   static const String value_class = 'value-class';
 
@@ -333,8 +337,18 @@ class ExperimentalFeatures {
     releaseVersion: Version.parse('2.14.0'),
   );
 
-  static final value_class = ExperimentalFeature(
+  static final unnamed_libraries = ExperimentalFeature(
     index: 21,
+    enableString: EnableString.unnamed_libraries,
+    isEnabledByDefault: IsEnabledByDefault.unnamed_libraries,
+    isExpired: IsExpired.unnamed_libraries,
+    documentation: 'Unnamed libraries',
+    experimentalReleaseVersion: null,
+    releaseVersion: null,
+  );
+
+  static final value_class = ExperimentalFeature(
+    index: 22,
     enableString: EnableString.value_class,
     isEnabledByDefault: IsEnabledByDefault.value_class,
     isExpired: IsExpired.value_class,
@@ -344,7 +358,7 @@ class ExperimentalFeatures {
   );
 
   static final variance = ExperimentalFeature(
-    index: 22,
+    index: 23,
     enableString: EnableString.variance,
     isEnabledByDefault: IsEnabledByDefault.variance,
     isExpired: IsExpired.variance,
@@ -420,6 +434,9 @@ class IsEnabledByDefault {
   /// Default state of the experiment "triple-shift"
   static const bool triple_shift = true;
 
+  /// Default state of the experiment "unnamed-libraries"
+  static const bool unnamed_libraries = false;
+
   /// Default state of the experiment "value-class"
   static const bool value_class = false;
 
@@ -494,6 +511,9 @@ class IsExpired {
   /// Expiration status of the experiment "triple-shift"
   static const bool triple_shift = true;
 
+  /// Expiration status of the experiment "unnamed-libraries"
+  static const bool unnamed_libraries = false;
+
   /// Expiration status of the experiment "value-class"
   static const bool value_class = false;
 
@@ -574,6 +594,10 @@ mixin _CurrentState {
   /// Current state for the flag "triple-shift"
   bool get triple_shift => isEnabled(ExperimentalFeatures.triple_shift);
 
+  /// Current state for the flag "unnamed-libraries"
+  bool get unnamed_libraries =>
+      isEnabled(ExperimentalFeatures.unnamed_libraries);
+
   /// Current state for the flag "value-class"
   bool get value_class => isEnabled(ExperimentalFeatures.value_class);
 

pkg/analyzer/lib/src/dart/analysis/file_state.dart

@@ -872,7 +872,7 @@ class FileState {
         }
       } else if (directive is LibraryDirective) {
         libraryDirective = UnlinkedLibraryDirective(
-          name: directive.name.name,
+          name: directive.name2?.name,
         );
       } else if (directive is PartDirective) {
         parts.add(

pkg/analyzer/lib/src/dart/analysis/library_analyzer.dart

@@ -704,7 +704,7 @@ class LibraryAnalyzer {
         directive.element = containerElement;
       } else if (directive is LibraryDirectiveImpl) {
         directive.element = containerElement;
-        libraryNameNode = directive.name;
+        libraryNameNode = directive.name2;
       } else if (directive is PartDirectiveImpl) {
         if (containerKind is LibraryFileKind &&
             containerElement is LibraryElementImpl) {

pkg/analyzer/lib/src/dart/analysis/unlinked_data.dart

@@ -181,7 +181,7 @@ class UnlinkedLibraryAugmentationDirective {
 }
 
 class UnlinkedLibraryDirective {
-  final String name;
+  final String? name;
 
   UnlinkedLibraryDirective({
     required this.name,
@@ -191,12 +191,12 @@ class UnlinkedLibraryDirective {
     SummaryDataReader reader,
   ) {
     return UnlinkedLibraryDirective(
-      name: reader.readStringUtf8(),
+      name: reader.readOptionalStringUtf8(),
     );
   }
 
   void write(BufferedSink sink) {
-    sink.writeStringUtf8(name);
+    sink.writeOptionalStringUtf8(name);
   }
 }
 

pkg/analyzer/lib/src/dart/ast/ast.dart

@@ -7804,7 +7804,7 @@ class LibraryDirectiveImpl extends DirectiveImpl implements LibraryDirective {
   Token libraryKeyword;
 
   /// The name of the library being defined.
-  LibraryIdentifierImpl _name;
+  LibraryIdentifierImpl? _name;
 
   /// The semicolon terminating the directive.
   @override
@@ -7817,7 +7817,7 @@ class LibraryDirectiveImpl extends DirectiveImpl implements LibraryDirective {
     required super.comment,
     required super.metadata,
     required this.libraryKeyword,
-    required LibraryIdentifierImpl name,
+    required LibraryIdentifierImpl? name,
     required this.semicolon,
   }) : _name = name {
     _becomeParentOf(_name);
@@ -7830,16 +7830,20 @@ class LibraryDirectiveImpl extends DirectiveImpl implements LibraryDirective {
   Token get firstTokenAfterCommentAndMetadata => libraryKeyword;
 
   @override
-  LibraryIdentifierImpl get name => _name;
+  @Deprecated('Use name2')
+  LibraryIdentifierImpl get name => _name!;
 
-  set name(LibraryIdentifier name) {
-    _name = _becomeParentOf(name as LibraryIdentifierImpl);
+  set name(LibraryIdentifier? name) {
+    _name = _becomeParentOf(name as LibraryIdentifierImpl?);
   }
 
+  @override
+  LibraryIdentifierImpl? get name2 => _name;
+
   @override
   ChildEntities get _childEntities => super._childEntities
     ..addToken('libraryKeyword', libraryKeyword)
-    ..addNode('name', name)
+    ..addNode('name', name2)
     ..addToken('semicolon', semicolon);
 
   @override
@@ -7848,7 +7852,7 @@ class LibraryDirectiveImpl extends DirectiveImpl implements LibraryDirective {
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _name.accept(visitor);
+    _name?.accept(visitor);
   }
 }
 

pkg/analyzer/lib/src/dart/ast/to_source_visitor.dart

@@ -793,7 +793,7 @@ class ToSourceVisitor implements AstVisitor<void> {
   void visitLibraryDirective(LibraryDirective node) {
     _visitNodeList(node.metadata, separator: ' ', suffix: ' ');
     sink.write('library ');
-    _visitNode(node.name);
+    _visitNode(node.name2);
     sink.write(';');
   }
 

pkg/analyzer/lib/src/dart/ast/utilities.dart

@@ -915,7 +915,7 @@ class AstComparator implements AstVisitor<bool> {
             node.documentationComment, other.documentationComment) &&
         _isEqualNodeLists(node.metadata, other.metadata) &&
         isEqualTokens(node.libraryKeyword, other.libraryKeyword) &&
-        isEqualNodes(node.name, other.name) &&
+        isEqualNodes(node.name2, other.name2) &&
         isEqualTokens(node.semicolon, other.semicolon);
   }
 
@@ -2780,7 +2780,7 @@ class NodeReplacer extends ThrowingAstVisitor<bool> {
 
   @override
   bool visitLibraryDirective(covariant LibraryDirectiveImpl node) {
-    if (identical(node.name, _oldNode)) {
+    if (identical(node.name2, _oldNode)) {
       node.name = _newNode as LibraryIdentifier;
       return true;
     }

pkg/analyzer/lib/src/fasta/ast_builder.dart

@@ -141,6 +141,9 @@ class AstBuilder extends StackListener {
   /// `true` if records are enabled
   final bool enableRecords;
 
+  /// `true` if unnamed-library behavior is enabled
+  final bool enableUnnamedLibraries;
+
   final FeatureSet _featureSet;
 
   final LineInfo _lineInfo;
@@ -163,6 +166,8 @@ class AstBuilder extends StackListener {
         enableEnhancedEnums = _featureSet.isEnabled(Feature.enhanced_enums),
         enableMacros = _featureSet.isEnabled(Feature.macros),
         enableRecords = _featureSet.isEnabled(Feature.records),
+        enableUnnamedLibraries =
+            _featureSet.isEnabled(Feature.unnamedLibraries),
         uri = uri ?? fileUri;
 
   @override
@@ -2131,13 +2136,20 @@ class AstBuilder extends StackListener {
   }
 
   @override
-  void endLibraryName(Token libraryKeyword, Token semicolon) {
+  void endLibraryName(Token libraryKeyword, Token semicolon, bool hasName) {
     assert(optional('library', libraryKeyword));
     assert(optional(';', semicolon));
     debugEvent("LibraryName");
 
-    var libraryName = pop() as List<SimpleIdentifier>;
-    var name = ast.libraryIdentifier(libraryName);
+    var libraryName = hasName ? pop() as List<SimpleIdentifier>? : null;
+
+    if (!hasName && !enableUnnamedLibraries) {
+      _reportFeatureNotEnabled(
+        feature: ExperimentalFeatures.unnamed_libraries,
+        startToken: libraryKeyword,
+      );
+    }
+    var name = libraryName == null ? null : ast.libraryIdentifier(libraryName);
     var metadata = pop() as List<Annotation>?;
     var comment = _findComment(metadata, libraryKeyword);
     directives.add(

pkg/analyzer/lib/src/generated/testing/ast_test_factory.dart

@@ -399,17 +399,20 @@ class AstTestFactory {
       astFactory.labeledStatement(labels, statement);
 
   static LibraryDirectiveImpl libraryDirective(
-          List<Annotation> metadata, LibraryIdentifier libraryName) =>
+          List<Annotation> metadata, LibraryIdentifier? libraryName) =>
       LibraryDirectiveImpl(
         comment: null,
         metadata: metadata,
         libraryKeyword: TokenFactory.tokenFromKeyword(Keyword.LIBRARY),
-        name: libraryName as LibraryIdentifierImpl,
+        name: libraryName as LibraryIdentifierImpl?,
         semicolon: TokenFactory.tokenFromType(TokenType.SEMICOLON),
       );
 
-  static LibraryDirectiveImpl libraryDirective2(String libraryName) =>
-      libraryDirective(<Annotation>[], libraryIdentifier2([libraryName]));
+  static LibraryDirectiveImpl libraryDirective2(String? libraryName) =>
+      libraryDirective(
+        <Annotation>[],
+        libraryName == null ? null : libraryIdentifier2([libraryName]),
+      );
 
   static LibraryIdentifierImpl libraryIdentifier(
           List<SimpleIdentifier> components) =>

pkg/analyzer/lib/src/summary2/ast_text_printer.dart

@@ -670,7 +670,7 @@ class AstTextPrinter extends ThrowingAstVisitor<void> {
   void visitLibraryDirective(LibraryDirective node) {
     _directive(node);
     _token(node.libraryKeyword);
-    node.name.accept(this);
+    node.name2?.accept(this);
     _token(node.semicolon);
   }
 

pkg/analyzer/lib/src/summary2/informative_data.dart

@@ -1423,8 +1423,11 @@ class _InformativeDataWriter {
     for (var directive in unit.directives) {
       firstDirective ??= directive;
       if (directive is LibraryDirective) {
-        nameOffset = directive.name.offset;
-        nameLength = directive.name.length;
+        final libraryName = directive.name2;
+        if (libraryName != null) {
+          nameOffset = libraryName.offset;
+          nameLength = libraryName.length;
+        }
         break;
       }
     }

pkg/analyzer/lib/src/summary2/library_builder.dart

@@ -760,9 +760,12 @@ class LibraryBuilder {
     var nameLength = 0;
     for (final directive in libraryUnitNode.directives) {
       if (directive is ast.LibraryDirective) {
-        name = directive.name.components.map((e) => e.name).join('.');
-        nameOffset = directive.name.offset;
-        nameLength = directive.name.length;
+        final nameIdentifier = directive.name2;
+        if (nameIdentifier != null) {
+          name = nameIdentifier.components.map((e) => e.name).join('.');
+          nameOffset = nameIdentifier.offset;
+          nameLength = nameIdentifier.length;
+        }
         break;
       }
     }

pkg/analyzer/test/generated/error_parser_test.dart

@@ -2172,12 +2172,6 @@ class Wrong<T> {
     expect(parameter.name, isNotNull);
   }
 
-  void test_missingNameInLibraryDirective() {
-    CompilationUnit unit = parseCompilationUnit("library;",
-        errors: [expectedError(ParserErrorCode.MISSING_IDENTIFIER, 7, 1)]);
-    expect(unit, isNotNull);
-  }
-
   void test_missingNameInPartOfDirective() {
     CompilationUnit unit = parseCompilationUnit("part of;",
         errors: [expectedError(ParserErrorCode.EXPECTED_STRING_LITERAL, 7, 1)]);
@@ -2837,6 +2831,18 @@ main() {
         errors: [expectedError(ParserErrorCode.UNEXPECTED_TOKEN, 7, 1)]);
   }
 
+  void test_unnamedLibraryDirective() {
+    CompilationUnit unit = parseCompilationUnit("library;",
+        errors: [expectedError(ParserErrorCode.EXPERIMENT_NOT_ENABLED, 0, 7)]);
+    expect(unit, isNotNull);
+  }
+
+  void test_unnamedLibraryDirective_enabled() {
+    CompilationUnit unit = parseCompilationUnit("library;",
+        featureSet: FeatureSets.latestWithExperiments);
+    expect(unit, isNotNull);
+  }
+
   void test_unterminatedString_at_eof() {
     // Although the "unterminated string" error message is produced by the
     // scanner, we need to verify that the parser can handle the tokens

pkg/analyzer/test/generated/parser_fasta_listener.dart

@@ -1021,9 +1021,9 @@ class ForwardingTestListener extends ForwardingListener {
   }
 
   @override
-  void endLibraryName(Token libraryKeyword, Token semicolon) {
+  void endLibraryName(Token libraryKeyword, Token semicolon, bool hasName) {
     end('LibraryName');
-    super.endLibraryName(libraryKeyword, semicolon);
+    super.endLibraryName(libraryKeyword, semicolon, hasName);
   }
 
   @override

pkg/analyzer/test/generated/simple_parser_test.dart

@@ -63,13 +63,13 @@ class SimpleParserTest extends FastaParserTestCase {
     return classDecl.implementsClause!;
   }
 
-  LibraryIdentifier parseLibraryIdentifier(String name) {
+  LibraryIdentifier? parseLibraryIdentifier(String name) {
     createParser('library $name;');
     CompilationUnit unit = parser.parseCompilationUnit2();
     expect(unit, isNotNull);
     expect(unit.directives, hasLength(1));
     var directive = unit.directives[0] as LibraryDirective;
-    return directive.name;
+    return directive.name2;
   }
 
   /// Parse the given [content] as a sequence of statements by enclosing it in a
@@ -1468,7 +1468,7 @@ void main() {final c = C<int, int Function(String)>();}
 
   void test_parseLibraryIdentifier_builtin() {
     String name = "deferred";
-    LibraryIdentifier identifier = parseLibraryIdentifier(name);
+    LibraryIdentifier identifier = parseLibraryIdentifier(name)!;
     expectNotNullIfNoErrors(identifier);
     assertNoErrors();
     expect(identifier.name, name);
@@ -1484,7 +1484,7 @@ void main() {final c = C<int, int Function(String)>();}
 
   void test_parseLibraryIdentifier_multiple() {
     String name = "a.b.c";
-    LibraryIdentifier identifier = parseLibraryIdentifier(name);
+    LibraryIdentifier identifier = parseLibraryIdentifier(name)!;
     expectNotNullIfNoErrors(identifier);
     assertNoErrors();
     expect(identifier.name, name);
@@ -1492,7 +1492,7 @@ void main() {final c = C<int, int Function(String)>();}
 
   void test_parseLibraryIdentifier_pseudo() {
     String name = "await";
-    LibraryIdentifier identifier = parseLibraryIdentifier(name);
+    LibraryIdentifier identifier = parseLibraryIdentifier(name)!;
     expectNotNullIfNoErrors(identifier);
     assertNoErrors();
     expect(identifier.name, name);
@@ -1501,7 +1501,7 @@ void main() {final c = C<int, int Function(String)>();}
 
   void test_parseLibraryIdentifier_single() {
     String name = "a";
-    LibraryIdentifier identifier = parseLibraryIdentifier(name);
+    LibraryIdentifier identifier = parseLibraryIdentifier(name)!;
     expectNotNullIfNoErrors(identifier);
     assertNoErrors();
     expect(identifier.name, name);

pkg/analyzer/test/generated/top_level_parser_test.dart

@@ -1121,32 +1121,32 @@ Function(int, String) v;
     expect(directive, TypeMatcher<LibraryDirective>());
     var libraryDirective = directive as LibraryDirective;
     expect(libraryDirective.libraryKeyword, isNotNull);
-    expect(libraryDirective.name, isNotNull);
+    expect(libraryDirective.name2, isNotNull);
     expect(libraryDirective.semicolon, isNotNull);
   }
 
   void test_parseDirective_library_1_component() {
     createParser("library a;");
     var lib = parseFullDirective() as LibraryDirective;
-    expect(lib.name.components, hasLength(1));
-    expect(lib.name.components[0].name, 'a');
+    expect(lib.name2!.components, hasLength(1));
+    expect(lib.name2!.components[0].name, 'a');
   }
 
   void test_parseDirective_library_2_components() {
     createParser("library a.b;");
     var lib = parseFullDirective() as LibraryDirective;
-    expect(lib.name.components, hasLength(2));
-    expect(lib.name.components[0].name, 'a');
-    expect(lib.name.components[1].name, 'b');
+    expect(lib.name2!.components, hasLength(2));
+    expect(lib.name2!.components[0].name, 'a');
+    expect(lib.name2!.components[1].name, 'b');
   }
 
   void test_parseDirective_library_3_components() {
     createParser("library a.b.c;");
     var lib = parseFullDirective() as LibraryDirective;
-    expect(lib.name.components, hasLength(3));
-    expect(lib.name.components[0].name, 'a');
-    expect(lib.name.components[1].name, 'b');
-    expect(lib.name.components[2].name, 'c');
+    expect(lib.name2!.components, hasLength(3));
+    expect(lib.name2!.components[0].name, 'a');
+    expect(lib.name2!.components[1].name, 'b');
+    expect(lib.name2!.components[2].name, 'c');
   }
 
   void test_parseDirective_library_annotation() {
@@ -1157,7 +1157,7 @@ Function(int, String) v;
     expect(directive, TypeMatcher<LibraryDirective>());
     var libraryDirective = directive as LibraryDirective;
     expect(libraryDirective.libraryKeyword, isNotNull);
-    expect(libraryDirective.name, isNotNull);
+    expect(libraryDirective.name2, isNotNull);
     expect(libraryDirective.semicolon, isNotNull);
     expect(libraryDirective.metadata, hasLength(1));
     expect(libraryDirective.metadata[0].name.name, 'A');
@@ -1172,12 +1172,18 @@ Function(int, String) v;
     expect(directive, TypeMatcher<LibraryDirective>());
     var libraryDirective = directive as LibraryDirective;
     expect(libraryDirective.libraryKeyword, isNotNull);
-    expect(libraryDirective.name, isNotNull);
+    expect(libraryDirective.name2, isNotNull);
     expect(libraryDirective.semicolon, isNotNull);
     expect(libraryDirective.metadata, hasLength(1));
     expect(libraryDirective.metadata[0].name.name, 'A');
   }
 
+  void test_parseDirective_library_unnamed() {
+    createParser("library;");
+    var lib = parseFullDirective() as LibraryDirective;
+    expect(lib.name2, isNull);
+  }
+
   void test_parseDirective_library_withDocumentationComment() {
     createParser('/// Doc\nlibrary l;');
     var directive = parseFullDirective() as LibraryDirective;
@@ -1904,7 +1910,7 @@ enum E {
     expect(directive, isNotNull);
     assertNoErrors();
     expect(directive.libraryKeyword, isNotNull);
-    expect(directive.name, isNotNull);
+    expect(directive.name2, isNotNull);
     expect(directive.semicolon, isNotNull);
   }
 

pkg/analyzer/test/generated/utilities_test.dart

@@ -1238,7 +1238,7 @@ library foo;
       destination: node,
       source: node,
       childAccessors: [
-        (node) => node.name,
+        (node) => node.name2!,
       ],
     );
   }

pkg/analyzer/test/src/dart/ast/to_source_visitor_test.dart

@@ -638,6 +638,13 @@ void f() {}
     _assertSource("", AstTestFactory.compilationUnit());
   }
 
+  void test_visitCompilationUnit_libraryWithoutName() {
+    _assertSource(
+      "library ;",
+      AstTestFactory.compilationUnit3([AstTestFactory.libraryDirective2(null)]),
+    );
+  }
+
   void test_visitCompilationUnit_script() {
     _assertSource(
         "!#/bin/dartvm", AstTestFactory.compilationUnit5("!#/bin/dartvm"));

pkg/analyzer/test/src/fasta/ast_builder_test.dart

@@ -748,6 +748,42 @@ LibraryAugmentationDirective
 ''');
   }
 
+  void test_library_with_name() {
+    var parseResult = parseStringWithErrors(r'''
+library name.and.dots;
+''');
+    parseResult.assertNoErrors();
+
+    var node = parseResult.findNode.library('library');
+    assertParsedNodeText(node, r'''
+LibraryDirective
+  libraryKeyword: library
+  name: LibraryIdentifier
+    components
+      SimpleIdentifier
+        token: name
+      SimpleIdentifier
+        token: and
+      SimpleIdentifier
+        token: dots
+  semicolon: ;
+''');
+  }
+
+  void test_library_without_name() {
+    var parseResult = parseStringWithErrors(r'''
+library;
+''');
+    parseResult.assertNoErrors();
+
+    var node = parseResult.findNode.library('library');
+    assertParsedNodeText(node, r'''
+LibraryDirective
+  libraryKeyword: library
+  semicolon: ;
+''');
+  }
+
   void test_mixin_implementsClause_recordType() {
     var parseResult = parseStringWithErrors(r'''
 class C {}

pkg/analyzer/test/util/feature_sets.dart

@@ -32,6 +32,11 @@ class FeatureSets {
     flags: [],
   );
 
+  static final FeatureSet language_2_19 = FeatureSet.fromEnableFlags2(
+    sdkLanguageVersion: Version.parse('2.19.0'),
+    flags: [],
+  );
+
   static final FeatureSet latest = FeatureSet.latestLanguageVersion();
 
   static final FeatureSet latestWithExperiments = FeatureSet.fromEnableFlags2(
@@ -43,6 +48,7 @@ class FeatureSets {
       EnableString.named_arguments_anywhere,
       EnableString.records,
       EnableString.super_parameters,
+      EnableString.unnamed_libraries,
     ],
   );
 

pkg/analyzer/tool/summary/mini_ast.dart

@@ -328,9 +328,11 @@ class MiniAstBuilder extends StackListener {
   }
 
   @override
-  void endLibraryName(Token libraryKeyword, Token semicolon) {
+  void endLibraryName(Token libraryKeyword, Token semicolon, bool hasName) {
     debugEvent("LibraryName");
-    pop(); // Library name
+    if (hasName) {
+      pop(); // Library name
+    }
     pop(); // Metadata
     pop(); // Comment
   }

pkg/analyzer_plugin/lib/utilities/navigation/navigation_dart.dart

@@ -399,7 +399,7 @@ class _DartNavigationComputerVisitor extends RecursiveAstVisitor<void> {
 
   @override
   void visitLibraryDirective(LibraryDirective node) {
-    computer._addRegionForNode(node.name, node.element2);
+    computer._addRegionForNode(node.name2, node.element2);
   }
 
   @override

pkg/front_end/lib/src/api_prototype/experimental_flags_generated.dart

@@ -227,6 +227,14 @@ class ExperimentalFlag {
       experimentEnabledVersion: const Version(2, 14),
       experimentReleasedVersion: const Version(2, 14));
 
+  static const ExperimentalFlag unnamedLibraries = const ExperimentalFlag(
+      name: 'unnamed-libraries',
+      isEnabledByDefault: false,
+      isExpired: false,
+      enabledVersion: const Version(2, 19),
+      experimentEnabledVersion: const Version(2, 19),
+      experimentReleasedVersion: const Version(2, 19));
+
   static const ExperimentalFlag valueClass = const ExperimentalFlag(
       name: 'value-class',
       isEnabledByDefault: false,
@@ -378,6 +386,10 @@ class GlobalFeatures {
   GlobalFeature get tripleShift =>
       _tripleShift ??= _computeGlobalFeature(ExperimentalFlag.tripleShift);
 
+  GlobalFeature? _unnamedLibraries;
+  GlobalFeature get unnamedLibraries => _unnamedLibraries ??=
+      _computeGlobalFeature(ExperimentalFlag.unnamedLibraries);
+
   GlobalFeature? _valueClass;
   GlobalFeature get valueClass =>
       _valueClass ??= _computeGlobalFeature(ExperimentalFlag.valueClass);
@@ -515,6 +527,11 @@ class LibraryFeatures {
       _tripleShift ??= globalFeatures._computeLibraryFeature(
           ExperimentalFlag.tripleShift, canonicalUri, libraryVersion);
 
+  LibraryFeature? _unnamedLibraries;
+  LibraryFeature get unnamedLibraries =>
+      _unnamedLibraries ??= globalFeatures._computeLibraryFeature(
+          ExperimentalFlag.unnamedLibraries, canonicalUri, libraryVersion);
+
   LibraryFeature? _valueClass;
   LibraryFeature get valueClass =>
       _valueClass ??= globalFeatures._computeLibraryFeature(
@@ -572,6 +589,8 @@ ExperimentalFlag? parseExperimentalFlag(String flag) {
       return ExperimentalFlag.testExperiment;
     case "triple-shift":
       return ExperimentalFlag.tripleShift;
+    case "unnamed-libraries":
+      return ExperimentalFlag.unnamedLibraries;
     case "value-class":
       return ExperimentalFlag.valueClass;
     case "variance":
@@ -619,6 +638,8 @@ final Map<ExperimentalFlag, bool> defaultExperimentalFlags = {
   ExperimentalFlag.testExperiment:
       ExperimentalFlag.testExperiment.isEnabledByDefault,
   ExperimentalFlag.tripleShift: ExperimentalFlag.tripleShift.isEnabledByDefault,
+  ExperimentalFlag.unnamedLibraries:
+      ExperimentalFlag.unnamedLibraries.isEnabledByDefault,
   ExperimentalFlag.valueClass: ExperimentalFlag.valueClass.isEnabledByDefault,
   ExperimentalFlag.variance: ExperimentalFlag.variance.isEnabledByDefault,
 };

pkg/front_end/lib/src/fasta/kernel/macro/annotation_parser.dart

@@ -1309,7 +1309,7 @@ class _MacroListener implements Listener {
   }
 
   @override
-  void endLibraryName(Token libraryKeyword, Token semicolon) {
+  void endLibraryName(Token libraryKeyword, Token semicolon, bool hasName) {
     _unexpected();
   }
 

pkg/front_end/lib/src/fasta/source/diet_listener.dart

@@ -438,9 +438,11 @@ class DietListener extends StackListenerImpl {
   }
 
   @override
-  void endLibraryName(Token libraryKeyword, Token semicolon) {
+  void endLibraryName(Token libraryKeyword, Token semicolon, bool hasName) {
     debugEvent("endLibraryName");
-    pop(); // Name.
+    if (hasName) {
+      pop(); // Name.
+    }
     pop(); // Annotations.
   }
 

pkg/front_end/lib/src/fasta/source/outline_builder.dart

@@ -832,14 +832,20 @@ class OutlineBuilder extends StackListenerImpl {
   }
 
   @override
-  void endLibraryName(Token libraryKeyword, Token semicolon) {
+  void endLibraryName(Token libraryKeyword, Token semicolon, bool hasName) {
     debugEvent("endLibraryName");
-    popCharOffset();
-    Object? name = pop();
+    Object? name = null;
+    if (hasName) {
+      popCharOffset();
+      name = pop();
+    }
     List<MetadataBuilder>? metadata = pop() as List<MetadataBuilder>?;
-    if (name is! ParserRecovery) {
+    if (name != null && name is! ParserRecovery) {
       libraryBuilder.name =
-          flattenName(name!, offsetForToken(libraryKeyword), uri);
+          flattenName(name, offsetForToken(libraryKeyword), uri);
+    } else {
+      reportIfNotEnabled(
+          libraryFeatures.unnamedLibraries, semicolon.charOffset, noLength);
     }
     libraryBuilder.metadata = metadata;
   }

pkg/front_end/lib/src/fasta/util/parser_ast_helper.dart

@@ -1275,9 +1275,9 @@ abstract class AbstractParserAstListener implements Listener {
   }
 
   @override
-  void endLibraryName(Token libraryKeyword, Token semicolon) {
+  void endLibraryName(Token libraryKeyword, Token semicolon, bool hasName) {
     LibraryNameEnd data = new LibraryNameEnd(ParserAstType.END,
-        libraryKeyword: libraryKeyword, semicolon: semicolon);
+        libraryKeyword: libraryKeyword, semicolon: semicolon, hasName: hasName);
     seen(data);
   }
 
@@ -4960,15 +4960,19 @@ class LibraryNameBegin extends ParserAstNode {
 class LibraryNameEnd extends ParserAstNode {
   final Token libraryKeyword;
   final Token semicolon;
+  final bool hasName;
 
   LibraryNameEnd(ParserAstType type,
-      {required this.libraryKeyword, required this.semicolon})
+      {required this.libraryKeyword,
+      required this.semicolon,
+      required this.hasName})
       : super("LibraryName", type);
 
   @override
   Map<String, Object?> get deprecatedArguments => {
         "libraryKeyword": libraryKeyword,
         "semicolon": semicolon,
+        "hasName": hasName,
       };
 }
 

pkg/front_end/lib/src/fasta/util/textual_outline.dart

@@ -768,7 +768,7 @@ class TextualOutlineListener extends Listener {
   }
 
   @override
-  void endLibraryName(Token libraryKeyword, Token semicolon) {
+  void endLibraryName(Token libraryKeyword, Token semicolon, bool hasName) {
     unsortableElementStartToChunk[libraryKeyword] =
         new _LibraryNameChunk(libraryKeyword, semicolon);
   }

pkg/front_end/parser_testcases/error_recovery/issue_48371_prime1.dart.expect

@@ -11,7 +11,7 @@ beginCompilationUnit(library)
     beginLibraryName(library)
       handleRecoverableError(Message[ExpectedIdentifierButGotKeyword, 'enum' can't be used as an identifier because it's a keyword., Try renaming this to be an identifier that isn't a keyword., {lexeme: enum}], enum, enum)
       handleIdentifier(enum, libraryName)
-    endLibraryName(library, ;)
+    endLibraryName(library, ;, true)
   endTopLevelDeclaration(main)
   beginMetadataStar(main)
   endMetadataStar(0)

pkg/front_end/parser_testcases/error_recovery/issue_48371_prime1.dart.intertwined.expect

@@ -16,7 +16,7 @@ parseUnit(library)
               listener: handleRecoverableError(Message[ExpectedIdentifierButGotKeyword, 'enum' can't be used as an identifier because it's a keyword., Try renaming this to be an identifier that isn't a keyword., {lexeme: enum}], enum, enum)
             listener: handleIdentifier(enum, libraryName)
         ensureSemicolon(enum)
-        listener: endLibraryName(library, ;)
+        listener: endLibraryName(library, ;, true)
   listener: endTopLevelDeclaration(main)
   parseTopLevelDeclarationImpl(;, Instance of 'DirectiveContext')
     parseMetadataStar(;)

pkg/front_end/test/parser_test_listener.dart

@@ -1387,11 +1387,11 @@ class ParserTestListener implements Listener {
   }
 
   @override
-  void endLibraryName(Token libraryKeyword, Token semicolon) {
+  void endLibraryName(Token libraryKeyword, Token semicolon, bool hasName) {
     indent--;
     seen(libraryKeyword);
     seen(semicolon);
-    doPrint('endLibraryName(' '$libraryKeyword, ' '$semicolon)');
+    doPrint('endLibraryName(' '$libraryKeyword, ' '$semicolon, ' '$hasName)');
   }
 
   @override

tools/experimental_features.yaml

@@ -17,8 +17,8 @@
 #   dart pkg/analyzer/tool/experiments/generate.dart
 #
 # Also, pkg/analyzer/lib/src/dart/analysis/driver.dart will need a bump in
-# DATA_VERSION if making changes that changes previous flags' "index", e.g.
-# if adding a new flag that doesn't happen to be lexicographically last.
+# DATA_VERSION if making changes that change the "index" of any previous flags,
+# e.g. if adding a new flag that doesn't happen to be lexicographically last.
 #
 # kernel:
 #   pkg/front_end/tool/fasta generate-experimental-flags
@@ -134,6 +134,9 @@ features:
   patterns:
     help: "Patterns"
 
+  unnamed-libraries:
+    help: "Unnamed libraries"
+
 # Experiment flag only used for testing.
   test-experiment:
     help: >-