[cfe] Compile if elements in lists and sets

If elements are compiled to if statements.  The type inference rules
including insertion of runtime checks are not yet implemented.

Change-Id: Iaa7ab709a7acacf952887b17ac1081a9fecd7cef
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/97200
Commit-Queue: Kevin Millikin <[email protected]>
Reviewed-by: Dmitry Stefantsov <[email protected]>

Author: Kevin Millikin

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

@@ -3652,6 +3652,8 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
     push(ifToken);
   }
 
+  void handleElseControlFlow(Token elseToken) {}
+
   @override
   void endIfControlFlow(Token token) {
     debugEvent("endIfControlFlow");

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

@@ -28,10 +28,13 @@ import 'package:kernel/visitor.dart'
 
 import '../problems.dart' show getFileUri, unsupported;
 
+/// Mixin for spread and control-flow elements.
+///
 /// Spread and control-flow elements are not truly expressions and they cannot
 /// appear in arbitrary expression contexts in the Kernel program.  They can
-/// only appear as elements in list or set literals.
-mixin _FakeExpressionMixin on Expression {
+/// only appear as elements in list or set literals.  They are translated into
+/// a lower-level representation and never serialized to .dill files.
+mixin CollectionElement on Expression {
   /// Spread and contol-flow elements are not expressions and do not have a
   /// static type.
   @override
@@ -48,7 +51,7 @@ mixin _FakeExpressionMixin on Expression {
 }
 
 /// A spread element in a list or set literal.
-class SpreadElement extends Expression with _FakeExpressionMixin {
+class SpreadElement extends Expression with CollectionElement {
   Expression expression;
   bool isNullAware;
 
@@ -71,7 +74,7 @@ class SpreadElement extends Expression with _FakeExpressionMixin {
 }
 
 /// An 'if' element in a list or set literal.
-class IfElement extends Expression with _FakeExpressionMixin {
+class IfElement extends Expression with CollectionElement {
   Expression condition;
   Expression then;
   Expression otherwise;
@@ -107,7 +110,7 @@ class IfElement extends Expression with _FakeExpressionMixin {
 }
 
 /// A 'for' element in a list or set literal.
-class ForElement extends Expression with _FakeExpressionMixin {
+class ForElement extends Expression with CollectionElement {
   final List<VariableDeclaration> variables; // May be empty, but not null.
   Expression condition; // May be null.
   final List<Expression> updates; // May be empty, but not null.
@@ -144,7 +147,7 @@ class ForElement extends Expression with _FakeExpressionMixin {
 }
 
 /// A 'for-in' element in a list or set literal.
-class ForInElement extends Expression with _FakeExpressionMixin {
+class ForInElement extends Expression with CollectionElement {
   VariableDeclaration variable; // Has no initializer.
   Expression iterable;
   Expression body;

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

@@ -11,10 +11,6 @@ class InferenceVisitor extends BodyVisitor1<void, DartType> {
 
   @override
   void defaultExpression(Expression node, DartType typeContext) {
-    if (node is IfElement) {
-      visitIfElement(node, typeContext);
-      return;
-    }
     unhandled("${node.runtimeType}", "InferenceVisitor", node.fileOffset,
         inferrer.helper.uri);
   }
@@ -25,11 +21,6 @@ class InferenceVisitor extends BodyVisitor1<void, DartType> {
         inferrer.helper.uri);
   }
 
-  visitIfElement(IfElement node, DartType typeContext) {
-    node.parent.replaceChild(node,
-        new InvalidExpression('unhandled if element in collection literal'));
-  }
-
   @override
   void visitInvalidExpression(InvalidExpression node, DartType typeContext) {}
 
@@ -665,6 +656,45 @@ class InferenceVisitor extends BodyVisitor1<void, DartType> {
     return null;
   }
 
+  DartType inferElement(
+      Expression element,
+      int index,
+      DartType inferredTypeArgument,
+      List<DartType> spreadTypes,
+      bool inferenceNeeded,
+      bool typeChecksNeeded) {
+    if (element is SpreadElement) {
+      DartType spreadType = inferrer.inferExpression(
+          element.expression,
+          new InterfaceType(inferrer.coreTypes.iterableClass,
+              <DartType>[inferredTypeArgument]),
+          inferenceNeeded || typeChecksNeeded,
+          isVoidAllowed: true);
+      if (typeChecksNeeded) {
+        spreadTypes[index] = spreadType;
+      }
+      // Use 'dynamic' for error recovery.
+      return getSpreadElementType(spreadType, element.isNullAware) ??
+          const DynamicType();
+    } else if (element is IfElement) {
+      inferrer.inferExpression(element.condition,
+          inferrer.coreTypes.boolClass.rawType, typeChecksNeeded,
+          isVoidAllowed: false);
+      inferElement(element.then, index, inferredTypeArgument, spreadTypes,
+          inferenceNeeded, typeChecksNeeded);
+      if (element.otherwise != null) {
+        inferElement(element.otherwise, index, inferredTypeArgument,
+            spreadTypes, inferenceNeeded, typeChecksNeeded);
+      }
+      // TODO(kmillikin): Implement inference rules for if elements.
+      return const DynamicType();
+    } else {
+      return inferrer.inferExpression(
+          element, inferredTypeArgument, inferenceNeeded || typeChecksNeeded,
+          isVoidAllowed: true);
+    }
+  }
+
   void visitListLiteralJudgment(
       ListLiteralJudgment node, DartType typeContext) {
     var listClass = inferrer.coreTypes.listClass;
@@ -692,32 +722,16 @@ class InferenceVisitor extends BodyVisitor1<void, DartType> {
         typeChecksNeeded ? new List<DartType>(node.expressions.length) : null;
     if (inferenceNeeded || typeChecksNeeded) {
       for (int i = 0; i < node.expressions.length; ++i) {
-        Expression judgment = node.expressions[i];
-        if (judgment is SpreadElement) {
-          DartType spreadType = inferrer.inferExpression(
-              judgment.expression,
-              new InterfaceType(inferrer.coreTypes.iterableClass,
-                  <DartType>[inferredTypeArgument]),
-              inferenceNeeded || typeChecksNeeded,
-              isVoidAllowed: true);
-          if (inferenceNeeded) {
-            formalTypes.add(listType.typeArguments[0]);
-          }
-          if (typeChecksNeeded) {
-            spreadTypes[i] = spreadType;
-          }
-          // Use 'dynamic' for error recovery.
-          actualTypes.add(
-              getSpreadElementType(spreadType, judgment.isNullAware) ??
-                  const DynamicType());
-        } else {
-          inferrer.inferExpression(judgment, inferredTypeArgument,
-              inferenceNeeded || typeChecksNeeded,
-              isVoidAllowed: true);
-          if (inferenceNeeded) {
-            formalTypes.add(listType.typeArguments[0]);
-          }
-          actualTypes.add(getInferredType(judgment, inferrer));
+        DartType type = inferElement(
+            node.expressions[i],
+            i,
+            inferredTypeArgument,
+            spreadTypes,
+            inferenceNeeded,
+            typeChecksNeeded);
+        actualTypes.add(type);
+        if (inferenceNeeded) {
+          formalTypes.add(listType.typeArguments[0]);
         }
       }
     }
@@ -777,6 +791,8 @@ class InferenceVisitor extends BodyVisitor1<void, DartType> {
                           1)));
             }
           }
+        } else if (item is IfElement) {
+          // TODO(kmillikin): Insert type checks on if elements.
         } else {
           inferrer.ensureAssignable(
               node.typeArgument, actualTypes[i], item, item.fileOffset,
@@ -1375,32 +1391,16 @@ class InferenceVisitor extends BodyVisitor1<void, DartType> {
         typeChecksNeeded ? new List<DartType>(node.expressions.length) : null;
     if (inferenceNeeded || typeChecksNeeded) {
       for (int i = 0; i < node.expressions.length; ++i) {
-        Expression judgment = node.expressions[i];
-        if (judgment is SpreadElement) {
-          DartType spreadType = inferrer.inferExpression(
-              judgment.expression,
-              new InterfaceType(inferrer.coreTypes.iterableClass,
-                  <DartType>[inferredTypeArgument]),
-              inferenceNeeded || typeChecksNeeded,
-              isVoidAllowed: true);
-          if (inferenceNeeded) {
-            formalTypes.add(setType.typeArguments[0]);
-          }
-          if (typeChecksNeeded) {
-            spreadTypes[i] = spreadType;
-          }
-          // Use 'dynamic' for error recovery.
-          actualTypes.add(
-              getSpreadElementType(spreadType, judgment.isNullAware) ??
-                  const DynamicType());
-        } else {
-          inferrer.inferExpression(judgment, inferredTypeArgument,
-              inferenceNeeded || typeChecksNeeded,
-              isVoidAllowed: true);
-          if (inferenceNeeded) {
-            formalTypes.add(setType.typeArguments[0]);
-          }
-          actualTypes.add(getInferredType(judgment, inferrer));
+        DartType type = inferElement(
+            node.expressions[i],
+            i,
+            inferredTypeArgument,
+            spreadTypes,
+            inferenceNeeded,
+            typeChecksNeeded);
+        actualTypes.add(type);
+        if (inferenceNeeded) {
+          formalTypes.add(setType.typeArguments[0]);
         }
       }
     }
@@ -1460,6 +1460,8 @@ class InferenceVisitor extends BodyVisitor1<void, DartType> {
                           1)));
             }
           }
+        } else if (item is IfElement) {
+          // TODO(kmillikin): Insert type checks on if elements.
         } else {
           inferrer.ensureAssignable(node.typeArgument, actualTypes[i],
               node.expressions[i], node.expressions[i].fileOffset,

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

@@ -28,18 +28,11 @@ class InferredTypeVisitor
 
   @override
   DartType defaultExpression(Expression node, TypeInferrerImpl inferrer) {
-    if (node is IfElement) {
-      return visitIfElement(node, inferrer);
-    }
     unhandled("${node.runtimeType}", "getInferredType", node.fileOffset,
         inferrer.uri);
     return const InvalidType();
   }
 
-  DartType visitIfElement(IfElement node, TypeInferrerImpl inferrer) {
-    return const BottomType();
-  }
-
   @override
   DartType visitIntLiteral(IntLiteral node, TypeInferrerImpl inferrer) {
     return inferrer.coreTypes.intClass.rawType;