[dart2js, ddc] Clean up conditional imports in dart2js_runtime_metrics

This CL:
* adds empty dart:_dart2js_only and dart:_ddc_only libraries for use in
  conditional imports,
* updates pkg/dart2js_runtime_metrics to use the new libraries rather
  than dart:_dart2js_runtime_metrics and dart:js,
* and removes some unnecessary libraries, including VM-specific
  implementations in pkg/dart2js_runtime_metrics and the DDC
  implementation of dart:_dart2js_runtime_metrics.

Change-Id: I9500aa303fa5ad8aba0e1d413f69957c268f3f11
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/350681
Reviewed-by: Sigmund Cherem <sigmund@google.com>

pkg/compiler/lib/src/kernel/dart2js_target.dart

@@ -260,6 +260,7 @@ const implicitlyUsedLibraries = <String>[
 const requiredLibraries = <String, List<String>>{
   'dart2js': [
     'dart:_async_status_codes',
+    'dart:_dart2js_only',
     'dart:_dart2js_runtime_metrics',
     'dart:_foreign_helper',
     'dart:_http',
@@ -301,6 +302,7 @@ const requiredLibraries = <String, List<String>>{
   ],
   'dart2js_server': [
     'dart:_async_status_codes',
+    'dart:_dart2js_only',
     'dart:_dart2js_runtime_metrics',
     'dart:_foreign_helper',
     'dart:_http',
@@ -360,6 +362,8 @@ class Dart2jsConstantsBackend extends ConstantsBackend {
 }
 
 class Dart2jsDartLibrarySupport extends CustomizedDartLibrarySupport {
-  const Dart2jsDartLibrarySupport()
-      : super(supported: const {'_dart2js_runtime_metrics'});
+  // This is required so that `dart.library._dart2js_only` can be used as an
+  // import condition. Libraries with leading underscores are otherwise
+  // considered unsupported regardless of the library specification.
+  const Dart2jsDartLibrarySupport() : super(supported: const {'_dart2js_only'});
 }

pkg/dart2js_runtime_metrics/lib/_runtime_metrics_vm.dart

@@ -1,12 +0,0 @@
-// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-/// A collection of metrics collected during the runtime of a Dart app.
-///
-/// The contents of the map depend on the platform. The map values are simple
-/// objects (strings, numbers, Booleans). There is always an entry for the key
-/// `'runtime'` with a [String] value.
-Map<String, Object> get runtimeMetrics {
-  return {'runtime': 'vm'};
-}

pkg/dart2js_runtime_metrics/lib/_startup_metrics_vm.dart

@@ -1,12 +0,0 @@
-// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-/// A collection of metrics for events that happen before `main()` is entered.
-///
-/// The contents of the map depend on the platform. The map values are simple
-/// objects (strings, numbers, Booleans). There is always an entry for the key
-/// `'runtime'` with a [String] value.
-Map<String, Object> get startupMetrics {
-  return {'runtime': 'vm'};
-}

pkg/dart2js_runtime_metrics/lib/null_safety.dart

@@ -3,5 +3,5 @@
 // BSD-style license that can be found in the LICENSE file.
 
 export '_null_safety_other.dart'
-    if (dart.library._dart2js_runtime_metrics) '_null_safety_dart2js.dart'
-    if (dart.library.js) '_null_safety_dartdevc.dart';
+    if (dart.library._dart2js_only) '_null_safety_dart2js.dart'
+    if (dart.library._ddc_only) '_null_safety_dartdevc.dart';

pkg/dart2js_runtime_metrics/lib/runtime_metrics.dart

@@ -3,6 +3,5 @@
 // BSD-style license that can be found in the LICENSE file.
 
 export '_runtime_metrics_unknown.dart'
-    if (dart.library._dart2js_runtime_metrics) '_runtime_metrics_dart2js.dart'
-    if (dart.library.ffi) '_runtime_metrics_vm.dart'
-    if (dart.library.js) '_runtime_metrics_dartdevc.dart';
+    if (dart.library._dart2js_only) '_runtime_metrics_dart2js.dart'
+    if (dart.library._ddc_only) '_runtime_metrics_dartdevc.dart';

pkg/dart2js_runtime_metrics/lib/startup_metrics.dart

@@ -3,6 +3,5 @@
 // BSD-style license that can be found in the LICENSE file.
 
 export '_startup_metrics_unknown.dart'
-    if (dart.library._dart2js_runtime_metrics) '_startup_metrics_dart2js.dart'
-    if (dart.library.ffi) '_startup_metrics_vm.dart'
-    if (dart.library.js) '_startup_metrics_dartdevc.dart';
+    if (dart.library._dart2js_only) '_startup_metrics_dart2js.dart'
+    if (dart.library._ddc_only) '_startup_metrics_dartdevc.dart';

pkg/dart2js_runtime_metrics/test/runtime_metrics_test.dart

@@ -12,7 +12,7 @@ void main() {
 
   String expectedRuntime;
   if (1.0 is! int) {
-    expectedRuntime = 'vm';
+    expectedRuntime = 'unknown';
   } else if (ClassWithLongName().toString().contains('minified:')) {
     // dart2js minified: "Instance of 'minified:xy'".
     expectedRuntime = 'dart2js';
@@ -42,7 +42,7 @@ void main() {
     return;
   }
 
-  if (expectedRuntime == 'vm') {
+  if (expectedRuntime == 'unknown') {
     return;
   }
 

pkg/dart2js_runtime_metrics/test/startup_metrics_test.dart

@@ -12,7 +12,7 @@ void main() {
 
   String expectedRuntime;
   if (1.0 is! int) {
-    expectedRuntime = 'vm';
+    expectedRuntime = 'unknown';
   } else if (ClassWithLongName().toString().contains('minified:')) {
     // dart2js minified: "Instance of 'minified:xy'".
     expectedRuntime = 'dart2js';
@@ -40,7 +40,7 @@ void main() {
     return;
   }
 
-  if (expectedRuntime == 'vm') {
+  if (expectedRuntime == 'unknown') {
     Expect.equals(1, metrics.length);
     return;
   }

pkg/dev_compiler/lib/src/kernel/target.dart

@@ -56,11 +56,11 @@ class DevCompilerTarget extends Target {
 
   @override
   List<String> get extraRequiredLibraries => const [
+        'dart:_ddc_only',
         'dart:_runtime',
         'dart:_js_shared_embedded_names',
         'dart:_recipe_syntax',
         'dart:_rti',
-        'dart:_dart2js_runtime_metrics',
         'dart:_debugger',
         'dart:_foreign_helper',
         'dart:_interceptors',
@@ -302,6 +302,17 @@ class DevCompilerTarget extends Target {
 
   @override
   ConstantsBackend get constantsBackend => const DevCompilerConstantsBackend();
+
+  @override
+  DartLibrarySupport get dartLibrarySupport =>
+      const DevCompilerDartLibrarySupport();
+}
+
+class DevCompilerDartLibrarySupport extends CustomizedDartLibrarySupport {
+  // This is required so that `dart.library._ddc_only` can be used as an import
+  // condition. Libraries with leading underscores are otherwise considered
+  // unsupported regardless of the library specification.
+  const DevCompilerDartLibrarySupport() : super(supported: const {'_ddc_only'});
 }
 
 /// Analyzes a component to determine if any covariance checks in private

pkg/dev_compiler/test/expression_compiler/scope_offset_test.dart

@@ -52,9 +52,10 @@ class ScopeOffsetValidator extends VisitorDefault<void> with VisitorVoidMixin {
   static void validate(Library library) {
     var validator = ScopeOffsetValidator._();
     validator.visitLibrary(library);
+    final importUri = library.importUri.toString();
     // TODO(joshualitt): Currently, there's nothing in `dart:_js_types` that
     // would be indexed. Remove this exception when we add things to it.
-    if (library.importUri.toString() != 'dart:_js_types') {
+    if (importUri != 'dart:_js_types' && importUri != 'dart:_ddc_only') {
       expect(validator.classCount + validator.memberCount, greaterThan(0),
           reason: 'Validation was not empty');
     }

pkg/kernel/lib/target/targets.dart

@@ -166,9 +166,9 @@ abstract class DartLibrarySupport {
   /// libraries specification.
   ///
   /// This is used to allow AOT to consider `dart:mirrors` as unsupported
-  /// despite it being supported in the platform dill, and dart2js to consider
-  /// `dart:_dart2js_runtime_metrics` to be supported despite it being an
-  /// internal library.
+  /// despite it being supported in the platform dill, and for dart2js and DDC
+  /// to consider `dart:_dart2js_only` and `dart:_ddc_only`, respectively, to be
+  /// supported despite them being internal libraries.
   bool computeDartLibrarySupport(String libraryName,
       {required bool isSupportedBySpec});
 

sdk/lib/_internal/js_dev_runtime/private/ddc_only.dart

@@ -0,0 +1,7 @@
+// Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// This library is only intended to be used to identify DDC in conditional
+/// imports and should not have any contents.
+library;

sdk/lib/_internal/js_dev_runtime/private/runtime_metrics.dart

@@ -1,10 +0,0 @@
-// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-// This file is a stub to allow dart:_dart2js_runtime_metrics to be discovered
-// across web contexts.
-
-get runtimeMetrics => throw UnimplementedError();
-
-get startupMetrics => throw UnimplementedError();

sdk/lib/_internal/js_runtime/lib/dart2js_only.dart

@@ -0,0 +1,7 @@
+// Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// This library is only intended to be used to identify dart2js in conditional
+/// imports and should not have any contents.
+library;

sdk/lib/_internal/sdk_library_metadata/lib/libraries.dart

@@ -224,6 +224,13 @@ const Map<String, LibraryInfo> libraries = const {
     documented: false,
     platforms: DART2JS_PLATFORM,
   ),
+  '_dart2js_only': const LibraryInfo(
+    '_internal/js_runtime/lib/dart2js_only.dart',
+    categories: '',
+    implementation: true,
+    documented: false,
+    platforms: DART2JS_PLATFORM,
+  ),
   '_dart2js_runtime_metrics': const LibraryInfo(
     '_internal/js_runtime/lib/dart2js_runtime_metrics.dart',
     categories: '',

sdk/lib/libraries.json

@@ -486,6 +486,9 @@
         "uri": "internal/internal.dart",
         "patches": "_internal/js_runtime/lib/internal_patch.dart"
       },
+      "_dart2js_only": {
+        "uri": "_internal/js_runtime/lib/dart2js_only.dart"
+      },
       "_dart2js_runtime_metrics": {
         "uri": "_internal/js_runtime/lib/dart2js_runtime_metrics.dart"
       },
@@ -580,8 +583,8 @@
       "_native_typed_data": {
         "uri": "_internal/js_dev_runtime/private/native_typed_data.dart"
       },
-      "_dart2js_runtime_metrics": {
-        "uri": "_internal/js_dev_runtime/private/runtime_metrics.dart"
+      "_ddc_only": {
+        "uri": "_internal/js_dev_runtime/private/ddc_only.dart"
       },
       "_rti": {
         "uri": "_internal/js_shared/lib/rti.dart"

sdk/lib/libraries.yaml

@@ -397,6 +397,9 @@ _dart2js_common:
       uri: "internal/internal.dart"
       patches: "_internal/js_runtime/lib/internal_patch.dart"
 
+    _dart2js_only:
+      uri: "_internal/js_runtime/lib/dart2js_only.dart"
+
     _dart2js_runtime_metrics:
       uri: "_internal/js_runtime/lib/dart2js_runtime_metrics.dart"
 
@@ -486,8 +489,8 @@ dartdevc:
     _native_typed_data:
       uri: "_internal/js_dev_runtime/private/native_typed_data.dart"
 
-    _dart2js_runtime_metrics:
-      uri: "_internal/js_dev_runtime/private/runtime_metrics.dart"
+    _ddc_only:
+      uri: "_internal/js_dev_runtime/private/ddc_only.dart"
 
     _rti:
       uri: "_internal/js_shared/lib/rti.dart"