Enable sound-flow-analysis for Dart 3.9.

Bug: #60438
Change-Id: I908d4e4a9143142281d8198870f40eba6cf6f67f
Tested: trybots
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/427500
Reviewed-by: Ivan Inozemtsev <iinozemtsev@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>
Reviewed-by: Morgan :) <davidmorgan@google.com>
Reviewed-by: Daco Harkes <dacoharkes@google.com>
Reviewed-by: Samuel Rawlins <srawlins@google.com>

Author: stereotype441

CHANGELOG.md

@@ -1,5 +1,15 @@
 ## 3.9.0
 
+### Language
+
+Dart 3.9 assumes null safety when computing type promotion, reachability, and
+definite assignment. This makes these features produce more accurate results for
+modern Dart programs. As a result of this change, more dead_code warnings may be
+produced. To take advantage of these improvements, set your package's [SDK
+constraint][language version] lower bound to 3.9 or greater (`sdk: '^3.9.0'`).
+
+[language version]: https://dart.dev/guides/language/evolution
+
 ### Tools
 
 #### Dart Development Compiler (dartdevc)

pkg/_fe_analyzer_shared/lib/src/experiments/flags.dart

@@ -222,10 +222,10 @@ enum ExperimentalFlag {
 
   soundFlowAnalysis(
       name: 'sound-flow-analysis',
-      isEnabledByDefault: false,
+      isEnabledByDefault: true,
       isExpired: false,
-      experimentEnabledVersion: defaultLanguageVersion,
-      experimentReleasedVersion: defaultLanguageVersion),
+      experimentEnabledVersion: const Version(3, 9),
+      experimentReleasedVersion: const Version(3, 9)),
 
   spreadCollections(
       name: 'spread-collections',

pkg/_fe_analyzer_shared/test/flow_analysis/reachability/data/equality_operator.dart

@@ -35,9 +35,9 @@ void nullableValue(int? x) {
 }
 
 void nonNullableValue(int x) {
-  if (x == null) {
+  if (x == null) /*unreachable*/{
     // Reachable since the value of x might come from legacy code
-    1;
+    /*stmt: unreachable*/1;
   } else {
     2;
   }
@@ -68,9 +68,9 @@ void potentiallyNullableTypeVar_nullableBound<T extends Object?>(T x) {
 }
 
 void nonNullableTypeVar<T extends Object>(T x) {
-  if (x == null) {
+  if (x == null) /*unreachable*/{
     // Reachable since the value of x might come from legacy code
-    1;
+    /*stmt: unreachable*/1;
   } else {
     2;
   }

pkg/_fe_analyzer_shared/test/flow_analysis/reachability/data/if_null.dart

@@ -12,18 +12,18 @@ void variable_if_null_assign_reachable(int? i) {
 
 void variable_if_null_unreachable(int i) {
   // Reachable since the value of i might come from legacy code
-  i ?? 0;
+  i ?? /*unreachable*/0;
 }
 
 void variable_if_null_assign_unreachable(int i) {
   // Reachable since the value of i might come from legacy code
-  i ??= 0;
+  /*cfe.update: unreachable*/i ??= /*unreachable*/0;
 }
 
 void variable_if_null_assign_unreachable_due_to_promotion(int? i) {
   if (i == null) return;
   // Reachable since the value of i might come from legacy code
-  i ??= 0;
+  /*cfe.update: unreachable*/i ??= /*unreachable*/0;
 }
 
 /*member: topLevelNullable:doesNotComplete*/
@@ -45,13 +45,13 @@ void top_level_if_null_assign_reachable() {
 void top_level_if_null_unreachable() {
   // Reachable since the value returned by topLevelNonNullGet might come from
   // legacy code
-  topLevelNonNullGet ?? 0;
+  topLevelNonNullGet ?? /*unreachable*/0;
 }
 
 void top_level_if_null_assign_unreachable() {
   // Reachable since the value returned by topLevelNonNullGet might come from
   // legacy code
-  topLevelNonNullGet ??= 0;
+  topLevelNonNullGet /*cfe.update: unreachable*/??= /*unreachable*/0;
 }
 
 class HasProperty<T> {
@@ -70,12 +70,12 @@ void property_if_null_assign_reachable(HasProperty<int?> x) {
 
 void property_if_null_unreachable(HasProperty<int> x) {
   // Reachable since the value returned by prop might come from legacy code
-  x.prop ?? 0;
+  x.prop ?? /*unreachable*/0;
 }
 
 void property_if_null_assign_unreachable(HasProperty<int> x) {
   // Reachable since the value returned by prop might come from legacy code
-  x.prop ??= 0;
+  x.prop ??= /*unreachable*/0;
 }
 
 void null_aware_property_if_null_reachable(HasProperty<int?>? x) {
@@ -94,7 +94,7 @@ void null_aware_property_if_null_not_shortened(HasProperty<int>? x) {
 
 void null_aware_property_if_null_assign_unreachable(HasProperty<int>? x) {
   // Reachable since the value returned by prop might come from legacy code.
-  x?.prop ??= 0;
+  x?.prop ??= /*unreachable*/0;
 }
 
 class SuperIntQuestionProperty extends HasProperty<int?> {
@@ -110,12 +110,12 @@ class SuperIntQuestionProperty extends HasProperty<int?> {
 class SuperIntProperty extends HasProperty<int> {
   void if_null_unreachable() {
     // Reachable since the value returned by prop might come from legacy code.
-    super.prop ?? 0;
+    super.prop ?? /*unreachable*/0;
   }
 
   void if_null_assign_unreachable() {
     // Reachable since the value returned by prop might come from legacy code.
-    super.prop ??= 0;
+    super.prop ??= /*unreachable*/0;
   }
 }
 
@@ -138,13 +138,13 @@ void extended_property_if_null_assign_reachable(HasProperty<int?> x) {
 void extended_property_if_null_unreachable(HasProperty<int> x) {
   // Reachable since the value returned by extendedProp might come from legacy
   // code.
-  x.extendedProp ?? 0;
+  x.extendedProp ?? /*unreachable*/0;
 }
 
 void extended_property_if_null_assign_unreachable(HasProperty<int> x) {
   // Reachable since the value returned by extendedProp might come from legacy
   // code.
-  x.extendedProp ??= 0;
+  x.extendedProp ??= /*unreachable*/0;
 }
 
 void null_aware_extended_property_if_null_reachable(HasProperty<int?>? x) {
@@ -166,7 +166,7 @@ void null_aware_extended_property_if_null_assign_unreachable(
     HasProperty<int>? x) {
   // Reachable since the value returned by extendedProp might come from legacy
   // code.
-  x?.extendedProp ??= 0;
+  x?.extendedProp ??= /*unreachable*/0;
 }
 
 void explicit_extended_property_if_null_reachable(HasProperty<int?> x) {
@@ -180,13 +180,13 @@ void explicit_extended_property_if_null_assign_reachable(HasProperty<int?> x) {
 void explicit_extended_property_if_null_unreachable(HasProperty<int> x) {
   // Reachable since the value returned by extendedProp might come from legacy
   // code.
-  ExtensionProperty(x).extendedProp ?? 0;
+  ExtensionProperty(x).extendedProp ?? /*unreachable*/0;
 }
 
 void explicit_extended_property_if_null_assign_unreachable(HasProperty<int> x) {
   // Reachable since the value returned by extendedProp might come from legacy
   // code.
-  ExtensionProperty(x).extendedProp ??= 0;
+  ExtensionProperty(x).extendedProp ??= /*unreachable*/0;
 }
 
 void null_aware_explicit_extended_property_if_null_reachable(
@@ -210,7 +210,7 @@ void null_aware_explicit_extended_property_if_null_assign_unreachable(
     HasProperty<int>? x) {
   // Reachable since the value returned by extendedProp might come from legacy
   // code.
-  ExtensionProperty(x)?.extendedProp ??= 0;
+  ExtensionProperty(x)?.extendedProp ??= /*unreachable*/0;
 }
 
 class Indexable<T> {
@@ -226,7 +226,7 @@ void index_if_null_reachable(Indexable<int?> x) {
 void index_if_null_unreachable(Indexable<int> x) {
   // Reachable since the value returned by operator[] might come from legacy
   // code.
-  x[0] ?? 0;
+  x[0] ?? /*unreachable*/0;
 }
 
 void index_if_null_assign_reachable(Indexable<int?> x) {
@@ -236,7 +236,7 @@ void index_if_null_assign_reachable(Indexable<int?> x) {
 void index_if_null_assign_unreachable(Indexable<int> x) {
   // Reachable since the value returned by operator[] might come from legacy
   // code.
-  x[0] ??= 0;
+  x[0] ??= /*unreachable*/0;
 }
 
 void null_aware_index_if_null_reachable(Indexable<int?>? x) {
@@ -256,7 +256,7 @@ void null_aware_index_if_null_assign_reachable(Indexable<int?>? x) {
 void null_aware_index_if_null_assign_unreachable(Indexable<int>? x) {
   // Reachable since the value returned by operator[] might come from legacy
   // code.
-  x?[0] ??= 0;
+  x?[0] ??= /*unreachable*/0;
 }
 
 class SuperIntQuestionIndex extends Indexable<int?> {
@@ -273,13 +273,13 @@ class SuperIntIndex extends Indexable<int> {
   void if_null_unreachable() {
     // Reachable since the value returned by operator[] might come from legacy
     // code.
-    super[0] ?? 0;
+    super[0] ?? /*unreachable*/0;
   }
 
   void if_null_assign_unreachable() {
     // Reachable since the value returned by operator[] might come from legacy
     // code.
-    super[0] ??= 0;
+    super[0] ??= /*unreachable*/0;
   }
 }
 
@@ -302,13 +302,13 @@ void extended_index_if_null_assign_reachable(HasProperty<int?> x) {
 void extended_index_if_null_unreachable(HasProperty<int> x) {
   // Reachable since the value returned by operator[] might come from legacy
   // code.
-  x[0] ?? 0;
+  x[0] ?? /*unreachable*/0;
 }
 
 void extended_index_if_null_assign_unreachable(HasProperty<int> x) {
   // Reachable since the value returned by operator[] might come from legacy
   // code.
-  x[0] ??= 0;
+  x[0] ??= /*unreachable*/0;
 }
 
 void null_aware_extended_index_if_null_reachable(HasProperty<int?>? x) {
@@ -328,7 +328,7 @@ void null_aware_extended_index_if_null_not_shortened(HasProperty<int>? x) {
 void null_aware_extended_index_if_null_assign_unreachable(HasProperty<int>? x) {
   // Reachable since the value returned by operator[] might come from legacy
   // code.
-  x?[0] ??= 0;
+  x?[0] ??= /*unreachable*/0;
 }
 
 void explicit_extended_index_if_null_reachable(HasProperty<int?> x) {
@@ -342,13 +342,13 @@ void explicit_extended_index_if_null_assign_reachable(HasProperty<int?> x) {
 void explicit_extended_index_if_null_unreachable(HasProperty<int> x) {
   // Reachable since the value returned by operator[] might come from legacy
   // code.
-  ExtensionIndex(x)[0] ?? 0;
+  ExtensionIndex(x)[0] ?? /*unreachable*/0;
 }
 
 void explicit_extended_index_if_null_assign_unreachable(HasProperty<int> x) {
   // Reachable since the value returned by operator[] might come from legacy
   // code.
-  ExtensionIndex(x)[0] ??= 0;
+  ExtensionIndex(x)[0] ??= /*unreachable*/0;
 }
 
 void null_aware_explicit_extended_index_if_null_reachable(
@@ -372,5 +372,5 @@ void null_aware_explicit_extended_index_if_null_assign_unreachable(
     HasProperty<int>? x) {
   // Reachable since the value returned by operator[] might come from legacy
   // code.
-  ExtensionIndex(x)?[0] ??= 0;
+  ExtensionIndex(x)?[0] ??= /*unreachable*/0;
 }