Implement type arguments in redirecting factories.

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

Index: pkg/front_end/lib/src/fasta/kernel/redirecting_factory_body.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/redirecting_factory_body.dart b/pkg/front_end/lib/src/fasta/kernel/redirecting_factory_body.dart
index 1fa7dd80fbc534085ebc48ef3453523d81fadbc0..205db064e47f64e17aa2d61affb4f1eef3d8050c 100644
--- a/pkg/front_end/lib/src/fasta/kernel/redirecting_factory_body.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/redirecting_factory_body.dart
@@ -6,46 +6,74 @@ library fasta.redirecting_factory_body;
 
 import 'package:kernel/ast.dart'
     show
+        DartType,
         Expression,
         ExpressionStatement,
         FunctionNode,
+        InterfaceType,
         InvalidExpression,
+        InvalidType,
         Let,
         Member,
         Procedure,
         StaticGet,
         StringLiteral,
+        TypeParameterType,
         VariableDeclaration;
 
+import 'package:kernel/type_algebra.dart' show Substitution;
+
 const String letName = "#redirecting_factory";
 
 class RedirectingFactoryBody extends ExpressionStatement {
-  RedirectingFactoryBody.internal(Expression value)
-      : super(new Let(new VariableDeclaration(letName, initializer: value),
+  Member cachedRedirectionTarget;
+
+  DartType cachedReturnType;
+
+  RedirectingFactoryBody.internal(Expression value, DartType type)
+      : super(new Let(
+            new VariableDeclaration(letName, initializer: value, type: type),
             new InvalidExpression()));
 
-  RedirectingFactoryBody(Member target) : this.internal(new StaticGet(target));
+  RedirectingFactoryBody(Member intermediateTarget, InterfaceType type)
+      : this.internal(new StaticGet(intermediateTarget), type);
 
   RedirectingFactoryBody.unresolved(String name)
-      : this.internal(new StringLiteral(name));
+      : this.internal(new StringLiteral(name), new InvalidType());
 
-  Member get target {
-    var value = getValue(expression);
+  Member get intermediateTarget {
+    var value = getVariable(expression)?.initializer;
     return value is StaticGet ? value.target : null;
   }
 
+  DartType get intermediateReturnType => getVariable(expression)?.type;
+
   String get unresolvedName {
-    var value = getValue(expression);
+    var value = getVariable(expression)?.initializer;
     return value is StringLiteral ? value.value : null;
   }
 
   bool get isUnresolved => unresolvedName != null;
 
-  static getValue(Expression expression) {
+  Member get target {
+    if (cachedReturnType == null) {
+      computeRedirectionTarget(this.parent.parent, this);
+    }
+    return cachedRedirectionTarget;
+  }
+
+  DartType get returnType {
+    if (cachedReturnType == null) {
+      computeRedirectionTarget(this.parent.parent, this);
+    }
+    return cachedReturnType;
+  }
+
+  static VariableDeclaration getVariable(Expression expression) {
     if (expression is Let) {
       VariableDeclaration variable = expression.variable;
       if (variable.name == letName) {
-        return variable.initializer;
+        return variable;
       }
     }
     return null;
@@ -57,32 +85,73 @@ class RedirectingFactoryBody extends ExpressionStatement {
     // [kernel_class_builder.dart](kernel_class_builder.dart).
     FunctionNode function = factory.function;
     ExpressionStatement statement = function.body;
+    VariableDeclaration variable = getVariable(statement.expression);
     function.body =
-        new RedirectingFactoryBody.internal(getValue(statement.expression))
+        new RedirectingFactoryBody.internal(variable.initializer, variable.type)
           ..parent = function;
   }
-}
 
-RedirectingFactoryBody getRedirectingFactoryBody(Member member) {
-  return member is Procedure && member.function.body is RedirectingFactoryBody
-      ? member.function.body
-      : null;
-}
+  static RedirectingFactoryBody getRedirectingFactoryBody(Member member) {
+    return member is Procedure && member.function.body is RedirectingFactoryBody
+        ? member.function.body
+        : null;
+  }
+
+  /// Iterate redirections from [factoryMethod].
+  static void iterateRedirections(
+      Member factoryMethod,
+      bool f(Member member, RedirectingFactoryBody body),
+      void onCycle(Member member, RedirectingFactoryBody body)) {
+    // We use the [tortoise and hare algorithm]
+    // (https://en.wikipedia.org/wiki/Cycle_detection#Tortoise_and_hare) to
+    // handle cycles.
 
-Member getRedirectionTarget(Procedure member) {
-  // We use the [tortoise and hare algorithm]
-  // (https://en.wikipedia.org/wiki/Cycle_detection#Tortoise_and_hare) to
-  // handle cycles.
-  Member tortoise = member;
-  RedirectingFactoryBody tortoiseBody = getRedirectingFactoryBody(tortoise);
-  Member hare = tortoiseBody?.target;
-  RedirectingFactoryBody hareBody = getRedirectingFactoryBody(hare);
-  while (tortoise != hare) {
-    if (tortoiseBody?.isUnresolved ?? true) return tortoise;
-    tortoise = tortoiseBody.target;
-    tortoiseBody = getRedirectingFactoryBody(tortoise);
-    hare = getRedirectingFactoryBody(hareBody?.target)?.target;
-    hareBody = getRedirectingFactoryBody(hare);
+    Member tortoise = factoryMethod;
+    RedirectingFactoryBody tortoiseBody = getRedirectingFactoryBody(tortoise);
+    Member hare = tortoiseBody?.intermediateTarget;
+    RedirectingFactoryBody hareBody = getRedirectingFactoryBody(hare);
+    while (tortoise != hare) {
+      if (tortoiseBody == null) return;
+      if (!f(tortoise, tortoiseBody)) return;
+      tortoise = tortoiseBody.intermediateTarget;
+      tortoiseBody = getRedirectingFactoryBody(tortoise);
+      hare = getRedirectingFactoryBody(hareBody?.intermediateTarget)
+          ?.intermediateTarget;
+      hareBody = getRedirectingFactoryBody(hare);
+    }
+    onCycle(tortoise, tortoiseBody);
+  }
+
+  static void computeRedirectionTarget(
+      Member factoryMethod, RedirectingFactoryBody body) {
+    DartType returnType = new InterfaceType(
+        factoryMethod.enclosingClass,
+        factoryMethod.function.typeParameters
+            .map((t) => new TypeParameterType(t))
+            .toList());
+    Member target;
+    iterateRedirections(factoryMethod,
+        (Member member, RedirectingFactoryBody body) {
+      if (body.isUnresolved) {
+        target = member;
+        returnType = const InvalidType();
+        return false; // Stop iterating.
+      }
+      target = body.intermediateTarget;
+      if (returnType is InterfaceType) {
+        InterfaceType interfaceType = returnType;
+        returnType = Substitution
+            .fromPairs(
+                member.function.typeParameters, interfaceType.typeArguments)
+            .substituteType(body.intermediateReturnType);
+      }
+      return true; // Continue iterating.
+    }, (Member member, RedirectingFactoryBody body) {
+      returnType = const InvalidType();
+      target = null;
+    });
+    body
+      ..cachedRedirectionTarget = target
+      ..cachedReturnType = returnType;
   }
-  return null;
 }