Add experimental flag inference-update-2.

This is initially intended to support type promotion of fields
(https://github.com/dart-lang/language/issues/2020).  However, if time
allows, we may roll other type inference improvements into it.

Change-Id: Ie4548ceafe671a9a328a11ad950a4e70f4d3ca41
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/244766
Reviewed-by: Devon Carew <devoncarew@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>

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

@@ -84,7 +84,7 @@ import 'package:meta/meta.dart';
 /// TODO(scheglov) Clean up the list of implicitly analyzed files.
 class AnalysisDriver implements AnalysisDriverGeneric {
   /// The version of data format, should be incremented on every format change.
-  static const int DATA_VERSION = 218;
+  static const int DATA_VERSION = 219;
 
   /// The number of exception contexts allowed to write. Once this field is
   /// zero, we stop writing any new exception contexts in this process.

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

@@ -22,6 +22,7 @@ final _knownFeatures = <String, ExperimentalFeature>{
   EnableString.extension_types: ExperimentalFeatures.extension_types,
   EnableString.generic_metadata: ExperimentalFeatures.generic_metadata,
   EnableString.inference_update_1: ExperimentalFeatures.inference_update_1,
+  EnableString.inference_update_2: ExperimentalFeatures.inference_update_2,
   EnableString.macros: ExperimentalFeatures.macros,
   EnableString.named_arguments_anywhere:
       ExperimentalFeatures.named_arguments_anywhere,
@@ -67,6 +68,9 @@ class EnableString {
   /// String to enable the experiment "inference-update-1"
   static const String inference_update_1 = 'inference-update-1';
 
+  /// String to enable the experiment "inference-update-2"
+  static const String inference_update_2 = 'inference-update-2';
+
   /// String to enable the experiment "macros"
   static const String macros = 'macros';
 
@@ -196,8 +200,18 @@ class ExperimentalFeatures {
     releaseVersion: null,
   );
 
-  static final macros = ExperimentalFeature(
+  static final inference_update_2 = ExperimentalFeature(
     index: 9,
+    enableString: EnableString.inference_update_2,
+    isEnabledByDefault: IsEnabledByDefault.inference_update_2,
+    isExpired: IsExpired.inference_update_2,
+    documentation: 'Type promotion for fields',
+    experimentalReleaseVersion: null,
+    releaseVersion: null,
+  );
+
+  static final macros = ExperimentalFeature(
+    index: 10,
     enableString: EnableString.macros,
     isEnabledByDefault: IsEnabledByDefault.macros,
     isExpired: IsExpired.macros,
@@ -207,7 +221,7 @@ class ExperimentalFeatures {
   );
 
   static final named_arguments_anywhere = ExperimentalFeature(
-    index: 10,
+    index: 11,
     enableString: EnableString.named_arguments_anywhere,
     isEnabledByDefault: IsEnabledByDefault.named_arguments_anywhere,
     isExpired: IsExpired.named_arguments_anywhere,
@@ -217,7 +231,7 @@ class ExperimentalFeatures {
   );
 
   static final non_nullable = ExperimentalFeature(
-    index: 11,
+    index: 12,
     enableString: EnableString.non_nullable,
     isEnabledByDefault: IsEnabledByDefault.non_nullable,
     isExpired: IsExpired.non_nullable,
@@ -227,7 +241,7 @@ class ExperimentalFeatures {
   );
 
   static final nonfunction_type_aliases = ExperimentalFeature(
-    index: 12,
+    index: 13,
     enableString: EnableString.nonfunction_type_aliases,
     isEnabledByDefault: IsEnabledByDefault.nonfunction_type_aliases,
     isExpired: IsExpired.nonfunction_type_aliases,
@@ -237,7 +251,7 @@ class ExperimentalFeatures {
   );
 
   static final set_literals = ExperimentalFeature(
-    index: 13,
+    index: 14,
     enableString: EnableString.set_literals,
     isEnabledByDefault: IsEnabledByDefault.set_literals,
     isExpired: IsExpired.set_literals,
@@ -247,7 +261,7 @@ class ExperimentalFeatures {
   );
 
   static final spread_collections = ExperimentalFeature(
-    index: 14,
+    index: 15,
     enableString: EnableString.spread_collections,
     isEnabledByDefault: IsEnabledByDefault.spread_collections,
     isExpired: IsExpired.spread_collections,
@@ -257,7 +271,7 @@ class ExperimentalFeatures {
   );
 
   static final super_parameters = ExperimentalFeature(
-    index: 15,
+    index: 16,
     enableString: EnableString.super_parameters,
     isEnabledByDefault: IsEnabledByDefault.super_parameters,
     isExpired: IsExpired.super_parameters,
@@ -267,7 +281,7 @@ class ExperimentalFeatures {
   );
 
   static final test_experiment = ExperimentalFeature(
-    index: 16,
+    index: 17,
     enableString: EnableString.test_experiment,
     isEnabledByDefault: IsEnabledByDefault.test_experiment,
     isExpired: IsExpired.test_experiment,
@@ -278,7 +292,7 @@ class ExperimentalFeatures {
   );
 
   static final triple_shift = ExperimentalFeature(
-    index: 17,
+    index: 18,
     enableString: EnableString.triple_shift,
     isEnabledByDefault: IsEnabledByDefault.triple_shift,
     isExpired: IsExpired.triple_shift,
@@ -288,7 +302,7 @@ class ExperimentalFeatures {
   );
 
   static final value_class = ExperimentalFeature(
-    index: 18,
+    index: 19,
     enableString: EnableString.value_class,
     isEnabledByDefault: IsEnabledByDefault.value_class,
     isExpired: IsExpired.value_class,
@@ -298,7 +312,7 @@ class ExperimentalFeatures {
   );
 
   static final variance = ExperimentalFeature(
-    index: 19,
+    index: 20,
     enableString: EnableString.variance,
     isEnabledByDefault: IsEnabledByDefault.variance,
     isExpired: IsExpired.variance,
@@ -338,6 +352,9 @@ class IsEnabledByDefault {
   /// Default state of the experiment "inference-update-1"
   static const bool inference_update_1 = false;
 
+  /// Default state of the experiment "inference-update-2"
+  static const bool inference_update_2 = false;
+
   /// Default state of the experiment "macros"
   static const bool macros = false;
 
@@ -403,6 +420,9 @@ class IsExpired {
   /// Expiration status of the experiment "inference-update-1"
   static const bool inference_update_1 = false;
 
+  /// Expiration status of the experiment "inference-update-2"
+  static const bool inference_update_2 = false;
+
   /// Expiration status of the experiment "macros"
   static const bool macros = false;
 
@@ -470,6 +490,10 @@ mixin _CurrentState {
   bool get inference_update_1 =>
       isEnabled(ExperimentalFeatures.inference_update_1);
 
+  /// Current state for the flag "inference-update-2"
+  bool get inference_update_2 =>
+      isEnabled(ExperimentalFeatures.inference_update_2);
+
   /// Current state for the flag "macros"
   bool get macros => isEnabled(ExperimentalFeatures.macros);
 

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

@@ -131,6 +131,14 @@ class ExperimentalFlag {
       experimentEnabledVersion: const Version(2, 18),
       experimentReleasedVersion: const Version(2, 18));
 
+  static const ExperimentalFlag inferenceUpdate2 = const ExperimentalFlag(
+      name: 'inference-update-2',
+      isEnabledByDefault: false,
+      isExpired: false,
+      enabledVersion: const Version(2, 18),
+      experimentEnabledVersion: const Version(2, 18),
+      experimentReleasedVersion: const Version(2, 18));
+
   static const ExperimentalFlag macros = const ExperimentalFlag(
       name: 'macros',
       isEnabledByDefault: false,
@@ -306,6 +314,10 @@ class GlobalFeatures {
   GlobalFeature get inferenceUpdate1 => _inferenceUpdate1 ??=
       _computeGlobalFeature(ExperimentalFlag.inferenceUpdate1);
 
+  GlobalFeature? _inferenceUpdate2;
+  GlobalFeature get inferenceUpdate2 => _inferenceUpdate2 ??=
+      _computeGlobalFeature(ExperimentalFlag.inferenceUpdate2);
+
   GlobalFeature? _macros;
   GlobalFeature get macros =>
       _macros ??= _computeGlobalFeature(ExperimentalFlag.macros);
@@ -415,6 +427,11 @@ class LibraryFeatures {
       _inferenceUpdate1 ??= globalFeatures._computeLibraryFeature(
           ExperimentalFlag.inferenceUpdate1, canonicalUri, libraryVersion);
 
+  LibraryFeature? _inferenceUpdate2;
+  LibraryFeature get inferenceUpdate2 =>
+      _inferenceUpdate2 ??= globalFeatures._computeLibraryFeature(
+          ExperimentalFlag.inferenceUpdate2, canonicalUri, libraryVersion);
+
   LibraryFeature? _macros;
   LibraryFeature get macros =>
       _macros ??= globalFeatures._computeLibraryFeature(
@@ -497,6 +514,8 @@ ExperimentalFlag? parseExperimentalFlag(String flag) {
       return ExperimentalFlag.genericMetadata;
     case "inference-update-1":
       return ExperimentalFlag.inferenceUpdate1;
+    case "inference-update-2":
+      return ExperimentalFlag.inferenceUpdate2;
     case "macros":
       return ExperimentalFlag.macros;
     case "named-arguments-anywhere":
@@ -544,6 +563,8 @@ final Map<ExperimentalFlag, bool> defaultExperimentalFlags = {
       ExperimentalFlag.genericMetadata.isEnabledByDefault,
   ExperimentalFlag.inferenceUpdate1:
       ExperimentalFlag.inferenceUpdate1.isEnabledByDefault,
+  ExperimentalFlag.inferenceUpdate2:
+      ExperimentalFlag.inferenceUpdate2.isEnabledByDefault,
   ExperimentalFlag.macros: ExperimentalFlag.macros.isEnabledByDefault,
   ExperimentalFlag.namedArgumentsAnywhere:
       ExperimentalFlag.namedArgumentsAnywhere.isEnabledByDefault,

tools/experimental_features.yaml

@@ -128,6 +128,9 @@ features:
   inference-update-1:
     help: "Horizontal type inference for function expressions passed to generic invocations."
 
+  inference-update-2:
+    help: "Type promotion for fields"
+
 # Experiment flag only used for testing.
   test-experiment:
     help: >-