In this question I've called the Delphi runtime source code "open source", simply because it's open. Others disagree with this because Delphi itself is a commercial product. According to Wikipedia, open source must comply to a set of rules.
I've done a quick scan in the Delphi license but can't find a clear note about it's licensing status. It does have a compiler-directive called DECLARE_GPL in system.pas which is the root for all other Delphi units. The system unit is the only unit that you don't need to add to your units since it's automatically added. Thus, if system.pas is GPL, anything that uses it would be GPL too! But Delphi is providing a dual-license for these source files so people could choose not to use the GPL license.
Still, if the Delphi source code is available and it supports the GPL, even though it also has a secondary license which could be applied too, would the Delphi runtime source code be open-source or not?
From system.pas of Delphi 2007:
(* The existence of the GPL symbol indicates that the System unit and the rest of the Delphi runtime library were compiled for use and distribution under the terms of the GNU General Public License (GPL).
Under the terms of the GPL, all applications compiled with the GPL version of the Delphi runtime library must also be distributed under the terms of the GPL. For more information about the GNU GPL, see http://www.gnu.org/copyleft/gpl.htmlThe GPL symbol does not exist in the Delphi runtime library purchased for commercial/proprietary software development.
If your source code needs to know which licensing model it is being compiled into, you can use {$IF DECLARED(GPL)}...{$IFEND} to test for the existence of the GPL symbol. The value of the symbol itself is not significant. *)
Especially this text inside the source makes me doubt about the license. If it's distributable as GPL, doesn't this mean it's also open-source?