[model][vm] Add Target flag for Closure Contexts in AST experiment

The flag is enabled in some of the bytecode generator tests.

Part of #61572

TEST=existing

Change-Id: I65f491d90aad3a8d923f1a740012bad0ae8f318a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/451280
Commit-Queue: Chloe Stefantsova <[email protected]>
Reviewed-by: Alexander Markov <[email protected]>

Author: chloestefantsova

pkg/dart2bytecode/lib/dart2bytecode.dart

@@ -226,8 +226,15 @@ Future<int> runCompilerWithOptions({
     ..invocationModes = InvocationMode.parseArguments(cfeInvocationModes)
     ..verbosity = verbosity;
 
+  final BytecodeOptions bytecodeOptions =
+      BytecodeOptions(enableAsserts: enableAsserts)
+        ..parseCommandLineFlags(bytecodeGeneratorOptions);
+
   compilerOptions.target = createFrontEndTarget(targetName,
-      trackWidgetCreation: trackWidgetCreation, supportMirrors: false);
+      trackWidgetCreation: trackWidgetCreation,
+      supportMirrors: false,
+      isClosureContextLoweringEnabled:
+          bytecodeOptions.isClosureContextLoweringEnabled);
   if (compilerOptions.target == null) {
     printMessage('Failed to create front-end target $targetName.');
     return badUsageExitCode;
@@ -248,10 +255,6 @@ Future<int> runCompilerWithOptions({
     return compileTimeErrorExitCode;
   }
 
-  final BytecodeOptions bytecodeOptions =
-      BytecodeOptions(enableAsserts: enableAsserts)
-        ..parseCommandLineFlags(bytecodeGeneratorOptions);
-
   if (bytecodeOptions.showBytecodeSizeStatistics) {
     BytecodeSizeStatistics.reset();
   }

pkg/dart2bytecode/lib/options.dart

@@ -13,6 +13,8 @@ class BytecodeOptions {
     'instance-field-initializers': 'Emit separate instance field initializers',
     'keep-unreachable-code':
         'Do not remove unreachable code (useful if collecting code coverage)',
+    'closure-context-lowering':
+        'Use the closure context lowering in Kernel AST instead of computing it',
   };
 
   bool enableAsserts;
@@ -24,6 +26,7 @@ class BytecodeOptions {
   bool omitAssertSourcePositions;
   bool keepUnreachableCode;
   bool showBytecodeSizeStatistics;
+  bool isClosureContextLoweringEnabled;
 
   BytecodeOptions({
     this.enableAsserts = false,
@@ -35,6 +38,7 @@ class BytecodeOptions {
     this.omitAssertSourcePositions = false,
     this.keepUnreachableCode = false,
     this.showBytecodeSizeStatistics = false,
+    this.isClosureContextLoweringEnabled = false,
   }) {}
 
   void parseCommandLineFlags(List<String>? flags) {
@@ -64,6 +68,9 @@ class BytecodeOptions {
         case 'show-bytecode-size-stat':
           showBytecodeSizeStatistics = true;
           break;
+        case 'closure-context-lowering':
+          isClosureContextLoweringEnabled = true;
+          break;
         default:
           throw 'Unexpected bytecode flag $flag';
       }

pkg/dart2bytecode/test/bytecode_generator_test.dart

@@ -30,8 +30,9 @@ const kUpdateExpectations = 'updateExpectations';
 
 final String dartSdkPkgDir = Platform.script.resolve('../..').toFilePath();
 
-runTestCase(Uri source) async {
-  final target = VmTarget(TargetFlags());
+runTestCase(Uri source, {bool isClosureContextLoweringEnabled = false}) async {
+  final target = VmTarget(TargetFlags(
+      isClosureContextLoweringEnabled: isClosureContextLoweringEnabled));
   Component component =
       await compileTestCaseToKernelProgram(source, target: target);
 
@@ -158,4 +159,19 @@ main() {
       }
     }
   });
+
+  group('gen-bytecode-with-closure-context-lowering', () {
+    final testCasesDir =
+        new Directory(dartSdkPkgDir + 'dart2bytecode/testcases');
+
+    for (var entry
+        in testCasesDir.listSync(recursive: true, followLinks: false)) {
+      if (entry.path.endsWith(".dart")) {
+        test(
+            entry.path,
+            () =>
+                runTestCase(entry.uri, isClosureContextLoweringEnabled: true));
+      }
+    }
+  });
 }

pkg/kernel/lib/target/targets.dart

@@ -15,13 +15,22 @@ class TargetFlags {
   final bool trackWidgetCreation;
   final bool supportMirrors;
 
+  /// Whether the backend expects closure contexts to be present in the AST.
+  ///
+  /// This flag is currently experimental. Generally, the backends rely on their
+  /// own analysis of captured variables to create closure contexts.
+  // TODO(cstefantsova): Update the comment when the feature is no longer
+  // experimental.
+  final bool isClosureContextLoweringEnabled;
+
   /// Indicator for the const backend setting "keep locals".
   /// Targets can overwrite based on other things.
   final bool? constKeepLocalsIndicator;
 
   const TargetFlags(
       {this.trackWidgetCreation = false,
       this.supportMirrors = true,
+      this.isClosureContextLoweringEnabled = false,
       this.constKeepLocalsIndicator});
 
   @override

pkg/vm/lib/kernel_front_end.dart

@@ -960,6 +960,7 @@ Target? createFrontEndTarget(
   bool trackWidgetCreation = false,
   bool supportMirrors = true,
   bool? constKeepLocalsIndicator,
+  bool isClosureContextLoweringEnabled = false,
 }) {
   // Make sure VM-specific targets are available.
   installAdditionalTargets();
@@ -968,6 +969,7 @@ Target? createFrontEndTarget(
     trackWidgetCreation: trackWidgetCreation,
     supportMirrors: supportMirrors,
     constKeepLocalsIndicator: constKeepLocalsIndicator,
+    isClosureContextLoweringEnabled: isClosureContextLoweringEnabled,
   );
   return getTarget(targetName, targetFlags);
 }