nitvm: Throw an error when trying to read an uninitialized attribute

[nit.git] / src / vm.nit

diff --git a/src/vm.nit b/src/vm.nit
index b5e5bb8..92d2d1f 100644 (file)
--- a/src/vm.nit
+++ b/src/vm.nit
@@ -44,6 +44,16 @@ class VirtualMachine super NaiveInterpreter
        # Handles memory and garbage collection
        var memory_manager: MemoryManager = new MemoryManager
 
+       # The unique instance of the `MInit` value
+       var initialization_value: Instance
+
+       init(modelbuilder: ModelBuilder, mainmodule: MModule, arguments: Array[String])
+       do
+               super
+               var init_type = new MInitType(mainmodule.model)
+               initialization_value = new MutableInstance(init_type)
+       end
+
        # Subtyping test for the virtual machine
        redef fun is_subtype(sub, sup: MType): Bool
        do
@@ -138,21 +148,22 @@ class VirtualMachine super NaiveInterpreter
 
                assert(recv isa MutableInstance)
 
-               recv.internal_attributes = init_internal_attributes(null_instance, recv.mtype.as(MClassType).mclass.all_mattributes(mainmodule, none_visibility).length)
+               recv.internal_attributes = init_internal_attributes(initialization_value, recv.mtype.as(MClassType).mclass.all_mattributes(mainmodule, none_visibility).length)
                super
        end
 
        # Initialize the internal representation of an object (its attribute values)
-       private fun init_internal_attributes(null_instance: Instance, size: Int): Pointer
+       # `init_instance` is the initial value of attributes
+       private fun init_internal_attributes(init_instance: Instance, size: Int): Pointer
                import Array[Instance].length, Array[Instance].[] `{
 
                Instance* attributes = malloc(sizeof(Instance) * size);
 
                int i;
                for(i=0; i<size; i++)
-                       attributes[i] = null_instance;
+                       attributes[i] = init_instance;
 
-               Instance_incr_ref(null_instance);
+               Instance_incr_ref(init_instance);
                return attributes;
        `}
 
@@ -170,6 +181,12 @@ class VirtualMachine super NaiveInterpreter
                var i = read_attribute_ph(recv.internal_attributes, recv.vtable.internal_vtable,
                                        recv.vtable.mask, id, mproperty.offset)
 
+               # If we get a `MInit` value, throw an error
+               if i == initialization_value then
+                       fatal("Uninitialized attribute {mproperty.name}")
+                       abort
+               end
+
                return i
        end
 
@@ -458,6 +475,29 @@ redef class MutableInstance
        var internal_attributes: Pointer
 end
 
+# Is the type of the initial value inside attributes
+class MInitType
+       super MType
+
+       redef var model: Model
+       protected init(model: Model)
+       do
+               self.model = model
+       end
+
+       redef fun to_s do return "InitType"
+       redef fun as_nullable do return self
+       redef fun need_anchor do return false
+       redef fun resolve_for(mtype, anchor, mmodule, cleanup_virtual) do return self
+       redef fun can_resolve_for(mtype, anchor, mmodule) do return true
+
+       redef fun collect_mclassdefs(mmodule) do return new HashSet[MClassDef]
+
+       redef fun collect_mclasses(mmodule) do return new HashSet[MClass]
+
+       redef fun collect_mtypes(mmodule) do return new HashSet[MClassType]
+end
+
 # A VTable contains the virtual method table for the dispatch
 # and informations to perform subtyping tests
 class VTable