Mixins with Generics

runtime/vm/class_finalizer.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/class_finalizer.h"
 
 #include "vm/flags.h"
 #include "vm/heap.h"
 #include "vm/isolate.h"
 #include "vm/longjump.h"
@@ skipping 1166 matching lines @@
                     function_name.ToCString(),
                     class_name.ToCString(),
                     function_name.ToCString(),
                     super_class_name.ToCString());
       }
     }
   }
 }
 
 
+// Copy the type parameters of the super and mixin classes to the
+// mixin application class. Change type arguments of super type to
+// refer to the respecive type parameters of the mixin application

[regis, 2013/03/14 23:40:34]

respective

[hausner, 2013/03/15 00:36:32]

Done.

+// class.
+void ClassFinalizer::CloneTypeParameters(const Class& mixapp_class) {
+  ASSERT(mixapp_class.NumTypeParameters() == 0);
+
+  const AbstractType& super_type =
+      AbstractType::Handle(mixapp_class.super_type());

[regis, 2013/03/14 23:40:34]

I would assert that the super type is not a MixinAppType, or the code of this
function will not do the right thing.
If it 'was' one (because of multiple mixins), it should have been resolved by
now and replaced by a Type.
You can simply assert that the super type is resolved, since a MixinAppType is
not resolved by definition.

[hausner, 2013/03/15 00:36:32]

Done.

+  const Class& super_class = Class::Handle(super_type.type_class());
+
+  const Type& mixin_type = Type::Handle(mixapp_class.mixin());
+  const Class& mixin_class = Class::Handle(mixin_type.type_class());
+
+  const int num_super_parameters = super_class.NumTypeParameters();
+  const int num_mixin_parameters = mixin_class.NumTypeParameters();
+  if ((num_super_parameters + num_mixin_parameters) == 0) {
+    return;
+  }
+
+  // First, clone the super class type parameters. Rename them so that
+  // there can be no name conflict between the parameters of the super
+  // class and the mixin class.
+  const TypeArguments& cloned_type_params = TypeArguments::Handle(
+      TypeArguments::New(num_super_parameters + num_mixin_parameters));
+  TypeParameter& param = TypeParameter::Handle();
+  TypeParameter& cloned_param = TypeParameter::Handle();
+  String& param_name = String::Handle();
+  AbstractType& param_bound = AbstractType::Handle();
+  int cloned_index = 0;
+  if (num_super_parameters > 0) {
+    const TypeArguments& super_params =
+        TypeArguments::Handle(super_class.type_parameters());
+    const TypeArguments& super_type_args =
+        TypeArguments::Handle(TypeArguments::New(num_super_parameters));
+    for (int i = 0; i < num_super_parameters; i++) {
+      param ^= super_params.TypeAt(i);
+      param_name = param.name();
+      param_bound = param.bound();
+      // TODO(hausner): handle type bounds.
+      if (!param_bound.IsObjectType()) {
+        const Script& script = Script::Handle(mixapp_class.script());
+        ReportError(script, param.token_pos(),
+                    "type parameter '%s': type bounds not yet"
+                    " implemented for mixins\n",
+                    param_name.ToCString());
+      }
+      param_name = String::Concat(param_name, Symbols::Backtick());
+      param_name = Symbols::New(param_name);
+      cloned_param = TypeParameter::New(mixapp_class,
+                                        cloned_index,
+                                        param_name,
+                                        param_bound,
+                                        param.token_pos());
+      cloned_type_params.SetTypeAt(cloned_index, cloned_param);
+      // Change the type arguments of the super type to refer to the
+      // cloned type parameters of the mixin application class.
+      super_type_args.SetTypeAt(cloned_index, cloned_param);
+      cloned_index++;
+    }
+    ASSERT(super_type.IsType());

[regis, 2013/03/14 23:40:34]

This may fail if the super type is a BoundedType. But it depends on how you are
going to handle bounds.

[hausner, 2013/03/15 00:36:32]

Added a todo that I need to handle BoundedType here. Need to discuss with you 
to understand when a super type can be bounded. In the super type chain the
parser creates and that we are dealing with here, there are no bounded types.

+    Type::Cast(super_type).set_arguments(super_type_args);
+  }
+
+  // Second, clone the type parameters of the mixin class.
+  // We need to retain the parameter names of the mixin class
+  // since the code that will be compiled in the context of the
+  // mixin application class may refer to the type parameters
+  // with that name.
+  if (num_mixin_parameters > 0) {
+    const TypeArguments& mixin_params =
+        TypeArguments::Handle(mixin_class.type_parameters());
+    for (int i = 0; i < num_mixin_parameters; i++) {
+      param ^= mixin_params.TypeAt(i);
+      param_name = param.name();
+      param_bound = param.bound();
+
+      // TODO(hausner): handle type bounds.
+      if (!param_bound.IsObjectType()) {
+        const Script& script = Script::Handle(mixapp_class.script());
+        ReportError(script, param.token_pos(),
+                    "type parameter '%s': type bounds not yet"
+                    " implemented for mixins\n",
+                    param_name.ToCString());
+      }
+      cloned_param = TypeParameter::New(mixapp_class,
+                                        cloned_index,
+                                        param_name,
+                                        param_bound,
+                                        param.token_pos());
+      cloned_type_params.SetTypeAt(cloned_index, cloned_param);
+      cloned_index++;
+    }
+  }
+  mixapp_class.set_type_parameters(cloned_type_params);
+}
+
+
 void ClassFinalizer::ApplyMixin(const Class& cls) {
   const Type& mixin_type = Type::Handle(cls.mixin());
   ASSERT(!mixin_type.IsNull());
   ASSERT(mixin_type.HasResolvedTypeClass());
   const Class& mixin_cls = Class::Handle(mixin_type.type_class());
 
   if (FLAG_trace_class_finalization) {
-    OS::Print("Applying mixin '%s' to '%s'\n",
+    OS::Print("Applying mixin '%s' to '%s' at pos %"Pd"\n",
               String::Handle(mixin_cls.Name()).ToCString(),
-              cls.ToCString());
+              cls.ToCString(),
+              cls.token_pos());
   }
 
   // Check that the super class of the mixin class is extending
   // class Object.
   const AbstractType& mixin_super_type =
       AbstractType::Handle(mixin_cls.super_type());
   if (!mixin_super_type.IsObjectType()) {
     const Script& script = Script::Handle(cls.script());
     const String& class_name = String::Handle(mixin_cls.Name());
     ReportError(script, cls.token_pos(),
                 "mixin class %s must extend class Object",
                 class_name.ToCString());
   }
 
-  // Copy the type parameters of the mixin class to the mixin
-  // application class.
-  const int num_type_parameters = mixin_cls.NumTypeParameters();
-  if (num_type_parameters > 0) {
-    ASSERT(cls.NumTypeParameters() == 0);
-    const TypeArguments& type_params =
-        TypeArguments::Handle(mixin_cls.type_parameters());
-    const TypeArguments& cloned_type_params =
-        TypeArguments::Handle(TypeArguments::New(num_type_parameters));
-    ASSERT(!type_params.IsNull());
-    TypeParameter& param = TypeParameter::Handle();
-    TypeParameter& cloned_param = TypeParameter::Handle();
-    String& param_name = String::Handle();
-    AbstractType& param_bound = AbstractType::Handle();
-    for (int i = 0; i < num_type_parameters; i++) {
-      param ^= type_params.TypeAt(i);
-      param_name = param.name();
-      param_bound = param.bound();
-      cloned_param = TypeParameter::New(
-          cls, i, param_name, param_bound, param.token_pos());
-      cloned_type_params.SetTypeAt(i, cloned_param);
-    }
-    cls.set_type_parameters(cloned_type_params);
-  }
+  // Copy type parameters to mixin application class.
+  CloneTypeParameters(cls);
 
   const GrowableObjectArray& cloned_funcs =
       GrowableObjectArray::Handle(GrowableObjectArray::New());
   Array& functions = Array::Handle();
   Function& func = Function::Handle();
   // The parser creates the mixin application class and adds just
   // one function, the implicit constructor.
   functions = cls.functions();
   ASSERT(functions.Length() == 1);
   func ^= functions.At(0);
@@ skipping 32 matching lines @@
   const intptr_t num_fields = fields.Length();
   for (int i = 0; i < num_fields; i++) {
     field ^= fields.At(i);
     if (!field.is_static()) {
       field = field.Clone(cls);
       cloned_fields.Add(field);
     }
   }
   fields = Array::MakeArray(cloned_fields);
   cls.SetFields(fields);
+
+  if (FLAG_trace_class_finalization) {
+    OS::Print("done mixin appl %s %s extending %s\n",
+              String::Handle(cls.Name()).ToCString(),
+              TypeArguments::Handle(cls.type_parameters()).ToCString(),
+              AbstractType::Handle(cls.super_type()).ToCString());
+  }
 }
 
 
 void ClassFinalizer::FinalizeClass(const Class& cls) {
   if (cls.is_finalized()) {
     return;
   }
   if (FLAG_trace_class_finalization) {
     OS::Print("Finalize %s\n", cls.ToCString());
   }
@@ skipping 147 matching lines @@
           !IsAliasCycleFree(type_class, visited)) {
         return false;
       }
     }
   }
   visited->RemoveLast();
   return true;
 }
 
 
+void ClassFinalizer::CopyArgs(const Class& cls,

[regis, 2013/03/14 23:40:34]

I would pick more meaningful names. What args are you copying? From where to
where? Actually, it is not just a copy operation. Maybe something like
ExtractTypeArguments or
void CollectTypeArguments(cls, type, collected_type_args)?

[hausner, 2013/03/15 00:36:32]

Done.

+                              const Type& type,
+                              const GrowableObjectArray& args) {
+  ASSERT(type.HasResolvedTypeClass());
+  Class& type_class = Class::Handle(type.type_class());
+  AbstractTypeArguments& type_args =
+      AbstractTypeArguments::Handle(type.arguments());
+  intptr_t num_type_parameters = type_class.NumTypeParameters();
+  intptr_t num_type_arguments = type_args.IsNull() ? 0 : type_args.Length();
+  AbstractType& arg = AbstractType::Handle();
+  if (num_type_arguments > 0) {
+    if (num_type_arguments != num_type_parameters) {
+      const Script& script = Script::Handle(cls.script());
+      const String& type_class_name = String::Handle(type_class.Name());
+      ReportError(script, type.token_pos(),
+          "wrong number of type arguments for class '%s'",
+          type_class_name.ToCString());
+    }
+    for (int i = 0; i < num_type_arguments; i++) {
+      arg = type_args.TypeAt(i);
+      args.Add(arg);
+    }
+  } else {
+    // Fill arguments with type dynamic.
+    for (int i = 0; i < num_type_parameters; i++) {
+      arg = Type::DynamicType();
+      args.Add(arg);
+    }
+  }
+}
+
+
+RawType* ClassFinalizer::ResolveMixinAppType(const Class& cls,
+                                             const MixinAppType& mixin_app) {
+  // Resolve super type and all mixin types.
+  const GrowableObjectArray& type_args =
+      GrowableObjectArray::Handle(GrowableObjectArray::New());
+  AbstractType& type = AbstractType::Handle(mixin_app.super_type());
+  ResolveType(cls, type, kCanonicalizeWellFormed);
+  ASSERT(type.HasResolvedTypeClass());
+  ASSERT(type.IsType());

[regis, 2013/03/14 23:40:34]

Not necessarily. It could be a BoundedType. Add a TODO for now, and you will
need lots of tests.

[hausner, 2013/03/15 00:36:32]

Same reasoning as above: the parser does not put a bounded type here. Added
TODO.

+  CopyArgs(cls, Type::Cast(type), type_args);
+  const Array& mixins = Array::Handle(mixin_app.mixin_types());
+  for (int i = 0; i < mixins.Length(); i++) {
+    type ^= mixins.At(i);
+    ASSERT(type.HasResolvedTypeClass());  // Newly created class in parser.
+    const Class& mixin_app_class = Class::Handle(type.type_class());
+    type = mixin_app_class.mixin();
+    ASSERT(!type.IsNull());
+    ResolveType(cls, type, kCanonicalizeWellFormed);
+    ASSERT(type.HasResolvedTypeClass());
+    ASSERT(type.IsType());
+    CopyArgs(cls, Type::Cast(type), type_args);
+  }
+  const TypeArguments& mixin_app_args =
+    TypeArguments::Handle(TypeArguments::New(type_args.Length()));
+  for (int i = 0; i < type_args.Length(); i++) {
+    type ^= type_args.At(i);
+    mixin_app_args.SetTypeAt(i, type);
+  }
+  if (FLAG_trace_class_finalization) {
+    OS::Print("ResolveMixinAppType: mixin appl type args: %s\n",
+              mixin_app_args.ToCString());
+  }
+  type ^= mixins.At(mixins.Length() - 1);

[regis, 2013/03/14 23:40:34]

Can you explain in a comment that the last type in the array represents the raw
type of the mixin app class?
Would it be cleaner to add a separate field of type Class rather than stuffing a
raw Type in the mixins array for this? 

[hausner, 2013/03/15 00:36:32]

Actually, all elements in the mixins array are mixin application types, a type
formed by the generated mixin application class and the type arguments parsed
from the source. I definitely want to make this nicer down the road. I would be
most happy if I could eliminate the MixinAppType again if I have a better grasp
on how to resolve and finalize the mixin applications.

+  const Class& resolved_mixin_app_class = Class::Handle(type.type_class());
+  Type& resolved_mixin_app_type = Type::Handle();
+  resolved_mixin_app_type = Type::New(resolved_mixin_app_class,
+                                      mixin_app_args,
+                                      mixin_app.token_pos());
+  return resolved_mixin_app_type.raw();
+}
+
+
 // Recursively walks the graph of explicitly declared super type and
 // interfaces, resolving unresolved super types and interfaces.
 // Reports an error if there is an interface reference that cannot be
 // resolved, or if there is a cycle in the graph. We detect cycles by
 // remembering interfaces we've visited in each path through the
 // graph. If we visit an interface a second time on a given path,
 // we found a loop.
 void ClassFinalizer::ResolveSuperTypeAndInterfaces(
     const Class& cls, GrowableArray<intptr_t>* visited) {
   ASSERT(visited != NULL);
   const intptr_t cls_index = cls.id();
   for (int i = 0; i < visited->length(); i++) {
     if ((*visited)[i] == cls_index) {
       // We have already visited class 'cls'. We found a cycle.
       const String& class_name = String::Handle(cls.Name());
       const Script& script = Script::Handle(cls.script());
       ReportError(script, cls.token_pos(),
                   "cyclic reference found for class '%s'",
                   class_name.ToCString());
     }
   }
 
   // If the class/interface has no explicit super class/interfaces
   // and is not a mixin application, we are done.
   AbstractType& super_type = AbstractType::Handle(cls.super_type());
-  Type& mixin_type = Type::Handle(cls.mixin());
   Array& super_interfaces = Array::Handle(cls.interfaces());
   if ((super_type.IsNull() || super_type.IsObjectType()) &&
-      (super_interfaces.Length() == 0) &&
-      (mixin_type.IsNull())) {
+      (super_interfaces.Length() == 0)) {
     return;
   }
 
-  if (!mixin_type.IsNull()) {
-    ResolveType(cls, mixin_type, kCanonicalizeWellFormed);
+  if (super_type.IsMixinAppType()) {
+    const MixinAppType& mixin_app_type = MixinAppType::Cast(super_type);
+    super_type = ResolveMixinAppType(cls, mixin_app_type);
+    cls.set_super_type(super_type);
   }
 
   // If cls belongs to core lib, restrictions about allowed interfaces
   // are lifted.
   const bool cls_belongs_to_core_lib = cls.library() == Library::CoreLibrary();
 
   // Resolve and check the super type and interfaces of cls.
   visited->Add(cls_index);
   AbstractType& interface = AbstractType::Handle();
   Class& interface_class = Class::Handle();
@@ skipping 295 matching lines @@
 void ClassFinalizer::ReportError(const char* format, ...) {
   va_list args;
   va_start(args, format);
   const Error& error = Error::Handle(
       Parser::FormatError(Script::Handle(), -1, "Error", format, args));
   va_end(args);
   ReportError(error);
 }
 
 }  // namespace dart