Implement generalized function types.

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

Index: pkg/front_end/lib/src/fasta/kernel/kernel_function_type_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_function_type_builder.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_function_type_builder.dart
index 9e05eb412429e84d6dd30f98ae957c3a307b4d8b..a1fe16acc6476fd1ea34479e634651b2aac17e9b 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_function_type_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_function_type_builder.dart
@@ -4,19 +4,38 @@
 
 library fasta.kernel_function_type_builder;
 
-import 'package:kernel/ast.dart' show DartType, DynamicType, Supertype;
+import 'package:kernel/ast.dart'
+    show
+        DartType,
+        DynamicType,
+        FunctionType,
+        NamedType,
+        Supertype,
+        TypeParameter;
 
 import 'kernel_builder.dart'
-    show FunctionTypeBuilder, KernelTypeBuilder, LibraryBuilder;
+    show
+        FormalParameterBuilder,
+        FunctionTypeBuilder,
+        KernelFormalParameterBuilder,
+        KernelTypeBuilder,
+        KernelTypeVariableBuilder,
+        LibraryBuilder,
+        TypeVariableBuilder;
 
 class KernelFunctionTypeBuilder extends FunctionTypeBuilder
     implements KernelTypeBuilder {
-  KernelFunctionTypeBuilder(int charOffset, Uri fileUri,
-      KernelTypeBuilder returnType, List typeVariables, List formals)
+  KernelFunctionTypeBuilder(
+      int charOffset,
+      Uri fileUri,
+      KernelTypeBuilder returnType,
+      List<TypeVariableBuilder> typeVariables,
+      List<FormalParameterBuilder> formals)
       : super(charOffset, fileUri, returnType, typeVariables, formals);
 
-  // TODO(ahe): Return a proper function type.
-  DartType build(LibraryBuilder library) => const DynamicType();
+  DartType build(LibraryBuilder library) {
+    return buildFunctionType(library, returnType, typeVariables, formals);
+  }
 
   Supertype buildSupertype(LibraryBuilder library) {
     library.addCompileTimeError(
@@ -25,3 +44,40 @@ class KernelFunctionTypeBuilder extends FunctionTypeBuilder
     return null;
   }
 }
+
+FunctionType buildFunctionType(
+    LibraryBuilder library,
+    KernelTypeBuilder returnType,
+    List<TypeVariableBuilder> typeVariables,
+    List<FormalParameterBuilder> formals) {
+  DartType builtReturnType = returnType?.build(library) ?? const DynamicType();
+  List<DartType> positionalParameters = <DartType>[];
+  List<NamedType> namedParameters;
+  int requiredParameterCount = 0;
+  if (formals != null) {
+    for (KernelFormalParameterBuilder formal in formals) {
+      DartType type = formal.type?.build(library) ?? const DynamicType();
+      if (formal.isPositional) {
+        positionalParameters.add(type);
+        if (formal.isRequired) requiredParameterCount++;
+      } else if (formal.isNamed) {
+        namedParameters ??= <NamedType>[];
+        namedParameters.add(new NamedType(formal.name, type));
+      }
+    }
+    if (namedParameters != null) {
+      namedParameters.sort();
+    }
+  }
+  List<TypeParameter> typeParameters;
+  if (typeVariables != null) {
+    typeParameters = <TypeParameter>[];
+    for (KernelTypeVariableBuilder t in typeVariables) {
+      typeParameters.add(t.parameter);
+    }
+  }
+  return new FunctionType(positionalParameters, builtReturnType,
+      namedParameters: namedParameters ?? const <NamedType>[],
+      typeParameters: typeParameters ?? const <TypeParameter>[],
+      requiredParameterCount: requiredParameterCount);
+}