fixed #336 (fixed casting an "empty" TValue to any other type)

Author: sglienke

Source/Base/Spring.pas

@@ -657,6 +657,8 @@   TValueHelper = record helper for TValue
     /// </summary>
     function IsString: Boolean;
 
+    function IsType(ATypeInfo: PTypeInfo): Boolean; overload;
+
     /// <summary>
     ///   Checks whether the stored value is a <c>Variant</c>.
     /// </summary>
@@ -669,6 +671,8 @@   TValueHelper = record helper for TValue
 
     function TryAsType(typeInfo: PTypeInfo; out target): Boolean; overload;
 
+    function TryCast(ATypeInfo: PTypeInfo; out AResult: TValue): Boolean;
+
     /// <summary>
     ///   Tries to convert the stored value. Returns false when the conversion
     ///   is not possible.
@@ -5740,6 +5744,13 @@ function TValueHelper.IsString: Boolean;
   Result := Kind in StringKinds;
 end;
 
+function TValueHelper.IsType(ATypeInfo: PTypeInfo): Boolean;
+var
+  unused: TValue;
+begin
+  Result := TryCast(ATypeInfo, unused);
+end;
+
 function TValueHelper.IsVariant: Boolean;
 begin
   Result := TypeInfo = System.TypeInfo(Variant);
@@ -6034,6 +6045,32 @@ function TValueHelper.TryAsType(typeInfo: PTypeInfo; out target): Boolean;
     value.ExtractRawData(@target);
 end;
 
+function TValueHelper.TryCast(ATypeInfo: PTypeInfo;
+  out AResult: TValue): Boolean;
+begin
+  // fix wrong logic in RTL:
+  // typecasting a TValue that contains a reference type that is nil succeeds
+  // in all cases which clearly is against the otherwise strict type cast rules
+
+  if not ((TValueData(Self).FTypeInfo = nil) or (TValueData(Self).FValueData = nil)) then
+    if IsEmpty and Assigned(ATypeInfo) and (Kind <> ATypeInfo.Kind) then
+      case Kind of
+        tkClass:
+          if not (ATypeInfo.Kind in [tkVariant, tkInterface, tkPointer]) then
+            Exit(False);
+        tkInterface:
+          if not (ATypeInfo.Kind in [tkVariant, tkPointer]) then
+            Exit(False);
+        tkDynArray:
+          if TValueData(Self).FTypeInfo <> ATypeInfo then
+            Exit(False);
+        tkPointer:;
+      else
+        Exit(False);
+      end;
+  Result := TValueHack(Self).TryCast(ATypeInfo, AResult);
+end;
+
 
 {$REGION 'Conversion functions'}
 type

Source/Core/Container/Spring.Container.Resolvers.pas

@@ -267,10 +267,10 @@ function TDependencyResolver.CanResolve(const context: ICreationContext;
   if CanResolveFromSubResolvers(context, dependency, argument) then
     Exit(True);
 
-  if argument.IsEmpty then
-    Result := Kernel.Registry.HasDefault(dependency.TypeInfo)
-  else if CanResolveFromArgument(context, dependency, argument) then
+  if CanResolveFromArgument(context, dependency, argument) then
     Result := True
+  else if argument.IsEmpty then
+    Result := Kernel.Registry.HasDefault(dependency.TypeInfo)
   else if argument.TryAsType(TypeInfo(TTypeKind), kind) and (kind = tkDynArray) then
     Result := Kernel.Registry.HasService(dependency.TypeInfo)
   else