Update ConstConditionalSimplifier's removal sentinel handling for

assertions

This matches the code pattern used elsewhere in this class as well as
the documentation for RemovingTransformer and brings it more in line
with the VM's unreachable code elimination.

Change-Id: Ica47f717be2bf72d84a7fbb2b78ad9cab1954407
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/373440
Reviewed-by: Johnni Winther <johnniwinther@google.com>

pkg/front_end/lib/src/kernel/const_conditional_simplifier.dart

@@ -81,8 +81,8 @@ class ConstConditionalSimplifier extends RemovingTransformer {
 
   @override
   TreeNode visitAssertBlock(AssertBlock node, TreeNode? removalSentinel) {
-    if (_removeAsserts && removalSentinel != null) {
-      return removalSentinel;
+    if (_removeAsserts) {
+      return removalSentinel ?? new EmptyStatement();
     } else {
       return super.visitAssertBlock(node, removalSentinel);
     }
@@ -91,8 +91,10 @@ class ConstConditionalSimplifier extends RemovingTransformer {
   @override
   TreeNode visitAssertInitializer(
       AssertInitializer node, TreeNode? removalSentinel) {
-    if (_removeAsserts && removalSentinel != null) {
-      return removalSentinel;
+    if (_removeAsserts) {
+      // Initializers only occur in the initializer list, where they are always
+      // removable.
+      return removalSentinel!;
     } else {
       return super.visitAssertInitializer(node, removalSentinel);
     }
@@ -101,8 +103,8 @@ class ConstConditionalSimplifier extends RemovingTransformer {
   @override
   TreeNode visitAssertStatement(
       AssertStatement node, TreeNode? removalSentinel) {
-    if (_removeAsserts && removalSentinel != null) {
-      return removalSentinel;
+    if (_removeAsserts) {
+      return removalSentinel ?? new EmptyStatement();
     } else {
       return super.visitAssertStatement(node, removalSentinel);
     }

pkg/front_end/test/coverage_suite_expected.dart

@@ -138,10 +138,10 @@ const Map<String, ({int hitCount, int missCount})> _expect = {
     hitCount: 96,
     missCount: 3,
   ),
-  // 50.67607289829512%.
+  // 50.795521508544496%.
   "package:front_end/src/base/incremental_compiler.dart": (
     hitCount: 862,
-    missCount: 839,
+    missCount: 835,
   ),
   // 0.0%.
   "package:front_end/src/base/incremental_serializer.dart": (
@@ -388,10 +388,10 @@ const Map<String, ({int hitCount, int missCount})> _expect = {
     hitCount: 518,
     missCount: 91,
   ),
-  // 71.23287671232876%.
+  // 69.86301369863014%.
   "package:front_end/src/compute_platform_binaries_location.dart": (
-    hitCount: 52,
-    missCount: 21,
+    hitCount: 51,
+    missCount: 22,
   ),
   // 100.0%.
   "package:front_end/src/dill/dill_builder_mixins.dart": (
@@ -478,10 +478,10 @@ const Map<String, ({int hitCount, int missCount})> _expect = {
     hitCount: 385,
     missCount: 31,
   ),
-  // 61.68831168831169%.
+  // 60.89743589743589%.
   "package:front_end/src/kernel/const_conditional_simplifier.dart": (
     hitCount: 95,
-    missCount: 59,
+    missCount: 61,
   ),
   // 69.72789115646259%.
   "package:front_end/src/kernel/constant_collection_builders.dart": (
@@ -758,9 +758,9 @@ const Map<String, ({int hitCount, int missCount})> _expect = {
     hitCount: 159,
     missCount: 20,
   ),
-  // 86.02836879432624%.
+  // 86.01845280340667%.
   "package:front_end/src/source/source_class_builder.dart": (
-    hitCount: 1213,
+    hitCount: 1212,
     missCount: 197,
   ),
   // 93.058568329718%.
@@ -778,10 +778,10 @@ const Map<String, ({int hitCount, int missCount})> _expect = {
     hitCount: 68,
     missCount: 38,
   ),
-  // 84.32539682539682%.
+  // 84.29423459244532%.
   "package:front_end/src/source/source_extension_type_declaration_builder.dart":
       (
-    hitCount: 425,
+    hitCount: 424,
     missCount: 79,
   ),
   // 92.22222222222223%.
@@ -799,14 +799,14 @@ const Map<String, ({int hitCount, int missCount})> _expect = {
     hitCount: 295,
     missCount: 35,
   ),
-  // 85.2467024914509%.
+  // 85.1680467608378%.
   "package:front_end/src/source/source_library_builder.dart": (
-    hitCount: 3490,
-    missCount: 604,
+    hitCount: 3497,
+    missCount: 609,
   ),
-  // 81.8988464951198%.
+  // 81.87472234562416%.
   "package:front_end/src/source/source_loader.dart": (
-    hitCount: 1846,
+    hitCount: 1843,
     missCount: 408,
   ),
   // 50.0%.

pkg/front_end/test/spell_checking_list_common.txt

@@ -2589,6 +2589,7 @@ remembered
 remembers
 reminder
 remote
+removable
 remove
 removed
 removes