[CMake] decision based on being a nested project

[Nathan Huesken]

Hi,

As can be read in an earlier thread, I am trying to nest a cmake
project (call it "inner") into another cmake project (call it "outer").
The "inner" project should be extracable and run as its own project.

Having trouble with EXTERNALPROJECT_ADD, I am trying to add the project
as a subdir. So I have something like this:
- rootdir
  CMakeFile: Project(outer)
  - lib
    CMakeFile: Add_Subdirectory(inner)
    - inner
      CMakeFile: Project(inner)
      - doc
        CMakeFile: Add_target(doc)
  - doc
    CMakeFile: Add_target(doc)
    ...

The problem now is, that the target "doc" exists twice, cmake
complaints.

So I would rename the inner target to "inner_doc", and add it as a
dependency of "doc".
But as said the inner project should also work on is own.
So I would do:

IF_IS_NESTED_PROJECT
  add_target(inner_doc)
ELSE
  add_target(doc)
ENDIF

My question: How can I find out if inner is configured as inner project
of outer or as a standalone project? (How can I do the
IF_IS_NESTED_PROJECT)?

Thanks!
Nathan