Begin writing a TypeInferenceListener interface.

pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart

Index: pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart b/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
index b4b6cfad15c09de3576979d2b06865d6f191a9b9..634115741fe67a1f8ab38b7153c16e1330aff7cb 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
@@ -4,6 +4,7 @@
 
 import 'package:front_end/src/base/instrumentation.dart';
 import 'package:front_end/src/fasta/type_inference/type_inference_engine.dart';
+import 'package:front_end/src/fasta/type_inference/type_inference_listener.dart';
 import 'package:front_end/src/fasta/type_inference/type_promotion.dart';
 import 'package:front_end/src/fasta/type_inference/type_schema.dart';
 import 'package:front_end/src/fasta/type_inference/type_schema_environment.dart';
@@ -84,11 +85,13 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
 
   final TypeSchemaEnvironment typeSchemaEnvironment;
 
+  final TypeInferenceListener listener;
+
   /// Context information for the current closure, or `null` if we are not
   /// inside a closure.
   _ClosureContext _closureContext;
 
-  TypeInferrerImpl(TypeInferenceEngineImpl<F> engine, this.uri)
+  TypeInferrerImpl(TypeInferenceEngineImpl<F> engine, this.uri, this.listener)
       : coreTypes = engine.coreTypes,
         strongMode = engine.strongMode,
         classHierarchy = engine.classHierarchy,
@@ -109,8 +112,11 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
   /// [inferExpression].
   DartType inferAsExpression(
       DartType typeContext, bool typeNeeded, E operand, DartType type) {
+    typeNeeded = listener.asExpressionEnter(typeContext) || typeNeeded;
     inferExpression(operand, null, false);

[Siggi Cherem (dart-lang), 2017/05/12 20:13:14]

is eventually the idea that if typeNeeded is false you can skip some of the
recursive calls in places like this?

[Paul Berry, 2017/05/12 20:22:21]

We can't skip the recursive calls (they are needed because it's possible that
subexpressions contain variable references that need to be promoted, closures
that need to have type inference performed within them, ets) but we can skip
some of the type manipulations.

-    return typeNeeded ? type : null;
+    var inferredType = typeNeeded ? type : null;
+    listener.asExpressionExit(inferredType);
+    return inferredType;
   }
 
   /// Performs the core type inference algorithm for boolean literals.
@@ -118,7 +124,10 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
   /// [typeContext], [typeNeeded], and the return value behave as described in
   /// [inferExpression].
   DartType inferBoolLiteral(DartType typeContext, bool typeNeeded) {
-    return typeNeeded ? coreTypes.boolClass.rawType : null;
+    typeNeeded = listener.boolLiteralEnter(typeContext) || typeNeeded;
+    var inferredType = typeNeeded ? coreTypes.boolClass.rawType : null;
+    listener.boolLiteralExit(inferredType);
+    return inferredType;
   }
 
   /// Performs the core type inference algorithm for conditional expressions.
@@ -130,6 +139,7 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
   /// type is reported via [setStaticType].
   DartType inferConditionalExpression(DartType typeContext, bool typeNeeded,
       E condition, E then, E otherwise, void setStaticType(DartType type)) {
+    typeNeeded = listener.conditionalExpressionEnter(typeContext) || typeNeeded;
     inferExpression(condition, coreTypes.boolClass.rawType, false);
     // TODO(paulberry): is it correct to pass the context down?
     DartType thenType = inferExpression(then, typeContext, true);
@@ -140,7 +150,9 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
     DartType type =
         typeSchemaEnvironment.getLeastUpperBound(thenType, otherwiseType);
     setStaticType(type);
-    return typeNeeded ? type : null;
+    var inferredType = typeNeeded ? type : null;
+    listener.conditionalExpressionExit(inferredType);
+    return inferredType;
   }
 
   /// Performs the core type inference algorithm for constructor invocations.
@@ -163,6 +175,7 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
       List<DartType> explicitTypeArguments,
       void forEachArgument(void callback(String name, E expression)),
       void setInferredTypeArguments(List<DartType> types)) {
+    typeNeeded = listener.constructorInvocationEnter(typeContext) || typeNeeded;
     List<DartType> inferredTypes;
     FunctionType constructorType = target.function.functionType;
     Substitution substitution;
@@ -215,13 +228,14 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
           new InstrumentationValueForTypeArgs(inferredTypes));
       setInferredTypeArguments(inferredTypes);
     }
+    DartType inferredType;
     if (typeNeeded) {
-      return substitution == null
+      inferredType = substitution == null
           ? targetClass.rawType
           : substitution.substituteType(targetClass.thisType);
-    } else {
-      return null;
     }
+    listener.constructorInvocationExit(inferredType);
+    return inferredType;
   }
 
   /// Maps the type of a variable's initializer expression to the correct
@@ -244,7 +258,10 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
   /// [typeContext], [typeNeeded], and the return value behave as described in
   /// [inferExpression].
   DartType inferDoubleLiteral(DartType typeContext, bool typeNeeded) {
-    return typeNeeded ? coreTypes.doubleClass.rawType : null;
+    typeNeeded = listener.doubleLiteralEnter(typeContext) || typeNeeded;
+    var inferredType = typeNeeded ? coreTypes.doubleClass.rawType : null;
+    listener.doubleLiteralExit(inferredType);
+    return inferredType;
   }
 
   /// Performs type inference on the given [expression].
@@ -293,6 +310,7 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
       int offset,
       void setReturnType(DartType type),
       DartType getFunctionType()) {
+    typeNeeded = listener.functionExpressionEnter(typeContext) || typeNeeded;
     // TODO(paulberry): do we also need to visit default parameter values?
     // TODO(paulberry): infer argument types and type parameters.
     // TODO(paulberry): full support for generators.
@@ -317,11 +335,9 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
       setReturnType(inferredReturnType);
     }
     _closureContext = oldClosureContext;
-    if (typeNeeded) {
-      return getFunctionType();
-    } else {
-      return null;
-    }
+    var inferredType = typeNeeded ? getFunctionType() : null;
+    listener.functionExpressionExit(inferredType);
+    return inferredType;
   }
 
   /// Performs the core type inference algorithm for if statements.
@@ -336,7 +352,10 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
   /// [typeContext], [typeNeeded], and the return value behave as described in
   /// [inferExpression].
   DartType inferIntLiteral(DartType typeContext, bool typeNeeded) {
-    return typeNeeded ? coreTypes.intClass.rawType : null;
+    typeNeeded = listener.intLiteralEnter(typeContext) || typeNeeded;
+    var inferredType = typeNeeded ? coreTypes.intClass.rawType : null;
+    listener.intLiteralExit(inferredType);
+    return inferredType;
   }
 
   /// Performs the core type inference algorithm for an "is" expression.
@@ -346,8 +365,11 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
   ///
   /// [operand] is the expression appearing to the left of "is".
   DartType inferIsExpression(DartType typeContext, bool typeNeeded, E operand) {
+    typeNeeded = listener.isExpressionEnter(typeContext) || typeNeeded;
     inferExpression(operand, null, false);
-    return typeNeeded ? coreTypes.boolClass.rawType : null;
+    var inferredType = typeNeeded ? coreTypes.boolClass.rawType : null;
+    listener.isExpressionExit(inferredType);
+    return inferredType;
   }
 
   /// Performs the core type inference algorithm for list literals.
@@ -361,6 +383,7 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
       DartType declaredTypeArgument,
       Iterable<E> expressions,
       void setTypeArgument(DartType typeArgument)) {
+    typeNeeded = listener.listLiteralEnter(typeContext) || typeNeeded;
     var listClass = coreTypes.listClass;
     var listType = listClass.thisType;
     List<DartType> inferredTypes;
@@ -399,9 +422,11 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
           new InstrumentationValueForTypeArgs([inferredTypeArgument]));
       setTypeArgument(inferredTypeArgument);
     }
-    return typeNeeded
+    var inferredType = typeNeeded
         ? new InterfaceType(listClass, [inferredTypeArgument])
         : null;
+    listener.listLiteralExit(inferredType);
+    return inferredType;
   }
 
   /// Performs the core type inference algorithm for method invocations.
@@ -428,6 +453,7 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
       void forEachArgument(void callback(String name, E expression)),
       void setInferredTypeArguments(List<DartType> types),
       void setInterfaceTarget(Procedure procedure)) {
+    typeNeeded = listener.methodInvocationEnter(typeContext) || typeNeeded;
     // First infer the receiver so we can look up the method that was invoked.
     var receiverType = inferExpression(receiver, null, true);
     // TODO(paulberry): can we share some of the code below with
@@ -491,13 +517,14 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
           new InstrumentationValueForTypeArgs(inferredTypes));
       setInferredTypeArguments(inferredTypes);
     }
+    DartType inferredType;
     if (typeNeeded) {
-      return substitution == null
+      inferredType = substitution == null
           ? memberFunctionType.returnType
           : substitution.substituteType(memberFunctionType.returnType);
-    } else {
-      return null;
     }
+    listener.methodInvocationExit(inferredType);
+    return inferredType;
   }
 
   /// Performs the core type inference algorithm for null literals.
@@ -505,7 +532,10 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
   /// [typeContext], [typeNeeded], and the return value behave as described in
   /// [inferExpression].
   DartType inferNullLiteral(DartType typeContext, bool typeNeeded) {
-    return typeNeeded ? coreTypes.nullClass.rawType : null;
+    typeNeeded = listener.nullLiteralEnter(typeContext) || typeNeeded;
+    var inferredType = typeNeeded ? coreTypes.nullClass.rawType : null;
+    listener.nullLiteralExit(inferredType);
+    return inferredType;
   }
 
   /// Performs the core type inference algorithm for static variable getters.
@@ -517,7 +547,10 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
   /// of the getter.
   DartType inferStaticGet(
       DartType typeContext, bool typeNeeded, DartType getterType) {
-    return typeNeeded ? getterType : null;
+    typeNeeded = listener.staticGetEnter(typeContext) || typeNeeded;
+    var inferredType = typeNeeded ? getterType : null;
+    listener.staticGetExit(inferredType);
+    return inferredType;
   }
 
   /// Performs the core type inference algorithm for string concatenations.
@@ -526,10 +559,13 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
   /// [inferExpression].
   DartType inferStringConcatenation(
       DartType typeContext, bool typeNeeded, Iterable<E> expressions) {
+    typeNeeded = listener.stringConcatenationEnter(typeContext) || typeNeeded;
     for (E expression in expressions) {
       inferExpression(expression, null, false);
     }
-    return typeNeeded ? coreTypes.stringClass.rawType : null;
+    var inferredType = typeNeeded ? coreTypes.stringClass.rawType : null;
+    listener.stringConcatenationExit(inferredType);
+    return inferredType;
   }
 
   /// Performs the core type inference algorithm for string literals.
@@ -537,7 +573,10 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
   /// [typeContext], [typeNeeded], and the return value behave as described in
   /// [inferExpression].
   DartType inferStringLiteral(DartType typeContext, bool typeNeeded) {
-    return typeNeeded ? coreTypes.stringClass.rawType : null;
+    typeNeeded = listener.stringLiteralEnter(typeContext) || typeNeeded;
+    var inferredType = typeNeeded ? coreTypes.stringClass.rawType : null;
+    listener.stringLiteralExit(inferredType);
+    return inferredType;
   }
 
   /// Performs the core type inference algorithm for variable declarations.
@@ -568,6 +607,7 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
       int offset,
       DartType declaredOrInferredType,
       void setPromotedType(DartType type)) {
+    typeNeeded = listener.variableGetEnter(typeContext) || typeNeeded;
     DartType promotedType = typePromoter.computePromotedType(
         typePromotionFact, typePromotionScope, mutatedInClosure);
     if (promotedType != null) {
@@ -575,12 +615,18 @@ abstract class TypeInferrerImpl<S, E, V, F> extends TypeInferrer<S, E, V, F> {
           new InstrumentationValueForType(promotedType));
     }
     setPromotedType(promotedType);
-    return typeNeeded ? (promotedType ?? declaredOrInferredType) : null;
+    var inferredType =
+        typeNeeded ? (promotedType ?? declaredOrInferredType) : null;
+    listener.variableGetExit(inferredType);
+    return inferredType;
   }
 
   DartType inferVariableSet(
       DartType typeContext, bool typeNeeded, DartType declaredType, E value) {
-    return inferExpression(value, declaredType, typeNeeded);
+    typeNeeded = listener.variableSetEnter(typeContext) || typeNeeded;
+    var inferredType = inferExpression(value, declaredType, typeNeeded);
+    listener.variableSetExit(inferredType);
+    return inferredType;
   }
 
   FunctionType _getCalleeFunctionType(DartType receiverType, Name methodName,