[cfe] Implement desugaring of switch expressions

Part of #49749

Closes #50814

Change-Id: Ie2524c7e5a1fc1a25f392eecbf2e444c89229923
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/277685
Commit-Queue: Chloe Stefantsova <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>
Reviewed-by: Aske Simon Christensen <[email protected]>

Author: chloestefantsova

pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart

@@ -11317,6 +11317,14 @@ const MessageCode messageSwitchCaseFallThrough = const MessageCode(
     analyzerCodes: <String>["CASE_BLOCK_NOT_TERMINATED"],
     problemMessage: r"""Switch case may fall through to the next case.""");
 
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Code<Null> codeSwitchExpressionEmpty = messageSwitchExpressionEmpty;
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const MessageCode messageSwitchExpressionEmpty = const MessageCode(
+    "SwitchExpressionEmpty",
+    problemMessage: r"""Switch expressions must contain at least one case.""");
+
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const Code<Null> codeSwitchExpressionNotAssignableCause =
     messageSwitchExpressionNotAssignableCause;

pkg/dart2wasm/lib/types.dart

@@ -510,7 +510,9 @@ class Types {
       // necessary to test the type arguments.
       Class cls = translator.classForType(operandType);
       InterfaceType? base = translator.hierarchy
-          .getTypeAsInstanceOf(type, cls, codeGen.member.enclosingLibrary)
+          .getTypeAsInstanceOf(type, cls,
+              isNonNullableByDefault:
+                  codeGen.member.enclosingLibrary.isNonNullableByDefault)
           ?.withDeclaredNullability(operandType.declaredNullability);
       if (base != operandType) {
         makeType(codeGen, type);

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

@@ -4145,7 +4145,7 @@ class BodyBuilder extends StackListenerImpl
       patterns[i] = toPattern(pop());
     }
     List<TypeBuilder>? typeArguments = pop() as List<TypeBuilder>?;
-    DartType typeArgument;
+    DartType? typeArgument;
     if (typeArguments != null) {
       if (typeArguments.length > 1) {
         addProblem(
@@ -4160,8 +4160,6 @@ class BodyBuilder extends StackListenerImpl
         typeArgument = instantiateToBounds(
             typeArgument, coreTypes.objectClass, libraryBuilder.library);
       }
-    } else {
-      typeArgument = implicitTypeArgument;
     }
 
     push(new ListPattern(typeArgument, patterns, leftBracket.charOffset));

pkg/front_end/lib/src/fasta/kernel/combined_member_signature.dart

@@ -718,7 +718,9 @@ abstract class CombinedMemberSignatureBase<T> {
       return type;
     }
     InterfaceType? instance = hierarchy.getTypeAsInstanceOf(
-        thisType, member.enclosingClass!, classBuilder.libraryBuilder.library);
+        thisType, member.enclosingClass!,
+        isNonNullableByDefault:
+            classBuilder.libraryBuilder.isNonNullableByDefault);
     assert(
         instance != null,
         "No instance of $thisType as ${member.enclosingClass} found for "

pkg/front_end/lib/src/fasta/kernel/forest.dart

@@ -399,7 +399,9 @@ class Forest {
     // ignore: unnecessary_null_comparison
     assert(fileOffset != null);
     // TODO(johnniwinther): Use [label]?
-    return new BreakStatementImpl(isContinue: false)..fileOffset = fileOffset;
+    return new BreakStatementImpl(isContinue: false)
+      ..fileOffset = fileOffset
+      ..target = label is LabeledStatement ? label : dummyLabeledStatement;
   }
 
   /// Return a representation of a catch clause.

pkg/front_end/lib/src/fasta/kernel/hierarchy/hierarchy_builder.dart

@@ -100,8 +100,8 @@ class ClassHierarchyBuilder implements ClassHierarchyBase {
   }
 
   @override
-  InterfaceType getTypeAsInstanceOf(
-      InterfaceType type, Class superclass, Library clientLibrary) {
+  InterfaceType getTypeAsInstanceOf(InterfaceType type, Class superclass,
+      {required bool isNonNullableByDefault}) {
     if (type.classNode == superclass) return type;
     return asSupertypeOf(type, superclass)!
         .asInterfaceType
@@ -122,14 +122,15 @@ class ClassHierarchyBuilder implements ClassHierarchyBase {
 
   @override
   InterfaceType getLegacyLeastUpperBound(
-      InterfaceType type1, InterfaceType type2, Library clientLibrary) {
+      InterfaceType type1, InterfaceType type2,
+      {required bool isNonNullableByDefault}) {
     if (type1 == type2) return type1;
 
     // LLUB(Null, List<dynamic>*) works differently for opt-in and opt-out
     // libraries.  In opt-out libraries the legacy behavior is preserved, so
     // LLUB(Null, List<dynamic>*) = List<dynamic>*.  In opt-out libraries the
     // rules imply that LLUB(Null, List<dynamic>*) = List<dynamic>?.
-    if (!clientLibrary.isNonNullableByDefault) {
+    if (!isNonNullableByDefault) {
       if (type1 is NullType) {
         return type2;
       }
@@ -153,10 +154,10 @@ class ClassHierarchyBuilder implements ClassHierarchyBase {
         continue;
       }
       if (nodes1.contains(node)) {
-        DartType candidate1 =
-            getTypeAsInstanceOf(type1, node.classBuilder.cls, clientLibrary);
-        DartType candidate2 =
-            getTypeAsInstanceOf(type2, node.classBuilder.cls, clientLibrary);
+        DartType candidate1 = getTypeAsInstanceOf(type1, node.classBuilder.cls,
+            isNonNullableByDefault: isNonNullableByDefault);
+        DartType candidate2 = getTypeAsInstanceOf(type2, node.classBuilder.cls,
+            isNonNullableByDefault: isNonNullableByDefault);
         if (candidate1 == candidate2) {
           common.add(node);
         }
@@ -172,7 +173,8 @@ class ClassHierarchyBuilder implements ClassHierarchyBase {
     for (int i = 0; i < common.length - 1; i++) {
       ClassHierarchyNode node = common[i];
       if (node.maxInheritancePath != common[i + 1].maxInheritancePath) {
-        return getTypeAsInstanceOf(type1, node.classBuilder.cls, clientLibrary)
+        return getTypeAsInstanceOf(type1, node.classBuilder.cls,
+                isNonNullableByDefault: isNonNullableByDefault)
             .withDeclaredNullability(
                 uniteNullabilities(type1.nullability, type2.nullability));
       } else {

pkg/front_end/lib/src/fasta/kernel/hierarchy/mixin_inferrer.dart

@@ -54,17 +54,17 @@ class TypeBuilderConstraintGatherer extends TypeConstraintGatherer
   CoreTypes get coreTypes => hierarchy.coreTypes;
 
   @override
-  void addLowerBound(
-      TypeConstraint constraint, DartType lower, Library clientLibrary) {
-    constraint.lower =
-        getStandardUpperBound(constraint.lower, lower, clientLibrary);
+  void addLowerBound(TypeConstraint constraint, DartType lower,
+      {required bool isNonNullableByDefault}) {
+    constraint.lower = getStandardUpperBound(constraint.lower, lower,
+        isNonNullableByDefault: isNonNullableByDefault);
   }
 
   @override
-  void addUpperBound(
-      TypeConstraint constraint, DartType upper, Library clientLibrary) {
-    constraint.upper =
-        getStandardLowerBound(constraint.upper, upper, clientLibrary);
+  void addUpperBound(TypeConstraint constraint, DartType upper,
+      {required bool isNonNullableByDefault}) {
+    constraint.upper = getStandardLowerBound(constraint.upper, upper,
+        isNonNullableByDefault: isNonNullableByDefault);
   }
 
   @override
@@ -75,7 +75,8 @@ class TypeBuilderConstraintGatherer extends TypeConstraintGatherer
   @override
   InterfaceType getTypeAsInstanceOf(InterfaceType type, Class superclass,
       Library clientLibrary, CoreTypes coreTypes) {
-    return hierarchy.getTypeAsInstanceOf(type, superclass, clientLibrary);
+    return hierarchy.getTypeAsInstanceOf(type, superclass,
+        isNonNullableByDefault: clientLibrary.isNonNullableByDefault);
   }
 
   @override