Is it legal to package the Cygwin installer executable — and some of its corresponding packages — and run it from another installer that installs a proprietary and commercially sold application?
The commercial application's source does not "build with" or "link to" any source code from any of the Cygwin source nor any of its packages' source. However, after the commercial application installs and is run, users can invoke some binaries that the Cygwin installer places onto the user's machine — namely bash.exe, mintty.exe, and tail.exe. Cygwin's licensing page claims that "Most of the tools are covered by the GNU GPL, some are public domain, and others have a X11 style license." I realize that distributors of binaries under the GNU GPL are required to include access to the source code for those binaries — which makes complete sense. However, does this mean that the entirety of the source code for the proprietary commercial application must also be distributed? My take is that no, it is not required, since the commercial application is deemed "a separate program" according to this statement in the GNU FAQ.
Can anybody shed some light on this situation?