[CMake] How to retrieve the property list dynamically?

[SF Markus Elfring]

> There are links to the "well known by CMake" properties that exist on various
> entities: global, directories, targets, tests, files, cache variables.

I have not overlooked the description for them.

I guess that these properties were extended during CMake history. I do not want 
to convert this part of the documentation into a separate data base for the 
support of enhanced queries. I would appreciate if the CMake programming 
interface can provide sophisticated introspection capabilities directly.


> However, the property mechanism allows project-specific extension of the set of
> properties on many of these entities. So these lists are incomplete.

How can such extensions be dynamically listed?


> Is there a concrete problem you are trying to solve by asking these questions?

Yes, of course. - My feature request is mostly for debugging purposes.

If there are problems or unexpected results for a target, I would like to know 
exactly which variables and properties were active in the affected situation.

Regards,
Markus