[dart2js] rename null-safety flag and plumb through CFE

The new flag name follows the changes in dart-lang/language#779, the change also is converging on not having each tool infer a default on the input, but rely on build systems to provide the appropriate flag instead.

Fixes dart-lang/sdk#39979

Change-Id: I39c143b7985dbfe6dab5dfd9a7347a7a4420479b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/138569
Commit-Queue: Sigmund Cherem <sigmund@google.com>
Reviewed-by: Mayank Patke <fishythefish@google.com>

Author: sigmundch

pkg/compiler/lib/src/commandline_options.dart

@@ -95,8 +95,8 @@ class Flags {
 
   static const String serverMode = '--server-mode';
 
-  static const String runtimeNullSafety = '--runtime-null-safety';
-  static const String noRuntimeNullSafety = '--no-runtime-null-safety';
+  static const String nullSafety = '--null-safety';
+  static const String noNullSafety = '--no-null-safety';
 
   static const String newDeferredSplit = '--new-deferred-split';
   static const String reportInvalidInferredDeferredTypes =

pkg/compiler/lib/src/dart2js.dart

@@ -465,8 +465,8 @@ Future<api.CompilationResult> compile(List<String> argv,
     new OptionHandler(Flags.laxRuntimeTypeToString, passThrough),
     new OptionHandler(Flags.benchmarkingProduction, passThrough),
     new OptionHandler(Flags.benchmarkingExperiment, passThrough),
-    new OptionHandler(Flags.runtimeNullSafety, setNullSafetyMode),
-    new OptionHandler(Flags.noRuntimeNullSafety, setNullSafetyMode),
+    new OptionHandler(Flags.nullSafety, setNullSafetyMode),
+    new OptionHandler(Flags.noNullSafety, setNullSafetyMode),
 
     // TODO(floitsch): remove conditional directives flag.
     // We don't provide the info-message yet, since we haven't publicly

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

@@ -105,7 +105,10 @@ class KernelLoaderTask extends CompilerTask {
             _options.librariesSpecificationUri,
             dependencies,
             _options.packageConfig,
-            experimentalFlags: _options.languageExperiments);
+            experimentalFlags: _options.languageExperiments,
+            nnbdMode: _options.useLegacySubtyping
+                ? fe.NnbdMode.Weak
+                : fe.NnbdMode.Strong);
         component = await fe.compile(
             initializedCompilerState,
             false,

pkg/compiler/lib/src/options.dart

@@ -335,13 +335,13 @@ class CompilerOptions implements DiagnosticOptions {
 
   /// When null-safety is enabled, whether the compiler should emit code with
   /// weak or strong semantics.
-  bool useWeakNullSafetySemantics = false;
+  bool _useWeakNullSafetySemantics = true;
 
   /// Whether to use legacy subtype semantics rather than null-safe semantics.
   /// This is `true` if null-safety is disabled, i.e. all code is legacy code,
   /// or if weak null-safety semantics are being used, since we do not emit
   /// warnings.
-  bool get useLegacySubtyping => !useNullSafety || useWeakNullSafetySemantics;
+  bool get useLegacySubtyping => !useNullSafety || _useWeakNullSafetySemantics;
 
   /// The path to the file that contains the profiled allocations.
   ///
@@ -468,11 +468,7 @@ class CompilerOptions implements DiagnosticOptions {
       ..codegenShards = _extractIntOption(options, '${Flags.codegenShards}=')
       ..cfeOnly = _hasOption(options, Flags.cfeOnly)
       ..debugGlobalInference = _hasOption(options, Flags.debugGlobalInference)
-      // TODO(sigmund): if no flag is specified, the default should depend on
-      // whether the entry point library is opted-in (see
-      // https://github.com/dart-lang/language/pull/779)
-      ..useWeakNullSafetySemantics =
-          _hasOption(options, Flags.noRuntimeNullSafety);
+      .._useWeakNullSafetySemantics = !_hasOption(options, Flags.nullSafety);
   }
 
   void validate() {

pkg/front_end/lib/src/api_unstable/dart2js.dart

@@ -33,6 +33,8 @@ import '../base/processed_options.dart' show ProcessedOptions;
 
 import '../base/libraries_specification.dart' show LibrariesSpecification;
 
+import '../base/nnbd_mode.dart' show NnbdMode;
+
 import '../fasta/compiler_context.dart' show CompilerContext;
 
 import '../kernel_generator_impl.dart' show generateKernelInternal;
@@ -109,6 +111,8 @@ export '../api_prototype/kernel_generator.dart' show kernelForProgram;
 
 export '../api_prototype/standard_file_system.dart' show DataFileSystemEntity;
 
+export '../base/nnbd_mode.dart' show NnbdMode;
+
 export '../compute_platform_binaries_location.dart'
     show computePlatformBinariesLocation;
 
@@ -133,7 +137,8 @@ InitializedCompilerState initializeCompiler(
     Uri packagesFileUri,
     {List<Uri> dependencies,
     Map<ExperimentalFlag, bool> experimentalFlags,
-    bool verify: false}) {
+    bool verify: false,
+    NnbdMode nnbdMode}) {
   additionalDills.sort((a, b) => a.toString().compareTo(b.toString()));
 
   if (oldState != null &&
@@ -151,6 +156,7 @@ InitializedCompilerState initializeCompiler(
     ..packagesFileUri = packagesFileUri
     ..experimentalFlags = experimentalFlags
     ..verify = verify;
+  if (nnbdMode != null) options.nnbdMode = nnbdMode;
 
   ProcessedOptions processedOpts = new ProcessedOptions(options: options);
 

tools/bots/test_matrix.json

@@ -529,7 +529,7 @@
           "non-nullable"
         ],
         "dart2js-options": [
-          "--no-runtime-null-safety"
+          "--no-null-safety"
         ],
         "use-sdk": true
       }
@@ -589,7 +589,7 @@
           "non-nullable"
         ],
         "dart2js-options": [
-          "--no-runtime-null-safety"
+          "--no-null-safety"
         ],
         "host-checked": true
       }