Easy to forget checking FIPS_IMPORT in a "dual use" project (import vs top-level)

[kaffeewolf]

When an imported project already contains a .fips-imports.cmake it will cause the libraries referenced by that project to be added twice, causing cmake to fail

Proof of concept: fips-import.zip

• fips-import-broken imports fips-import which imports fips-glew.
• running fips gen in fips-import-broken with a clean fips-import project succeeds
• running fips gen in the fips-import and then again in fips-import-broken fails with

CMake Error at D:/devel/fipstest/fips/cmake/fips.cmake:299 (add_library):
  add_library cannot create target "glew" because another target with the
  same name already exists.  The existing target is a static library created
  in source directory "D:/devel/fipstest/fips-glew".  See documentation for
  policy CMP0002 for more details.
Call Stack (most recent call first):
  D:/devel/fipstest/fips-glew/CMakeLists.txt:17 (fips_end_lib)

Note: the urls in the fips-imports projects are obviously wrong, but it doesnt matter as they are already present in the folder structure.

CMake version 3.14.1, python 3.6 and 3.7

[floooh]

Ok, I can reproduce by first running fips gen in fips-import, and then in fips-import-broken.

I think the bug is that the .fips-imports.cmake of dependencies seems to be included in top level projects, that shouldn't happen. Only the .fips-imports.cmake file in the top-level project itself is relevant. I'm surprised this problem didn't show up yet :)

[floooh]

Ah alright, I found the underlying problem, but I agree that the fix isn't a very good solution...

Basically the top-level CMakeLists.txt file in fips-import looks like this:

cmake_minimum_required(VERSION 2.8)
get_filename_component(FIPS_ROOT_DIR "../fips" ABSOLUTE)
include("${FIPS_ROOT_DIR}/cmake/fips.cmake")

fips_setup()
fips_project(fips-import)
fips_begin_lib(dummy)
fips_src(dummy)
fips_deps(glew)
fips_end_lib()
fips_finish()

fips_setup() and fips_finish() are always called, no matter if this is used as a top-level project, or used as an imported project.

For such "dual-use" projects, the top-part up to (and including) fips_project() and the final fips_finish() must be excluded if the variable FIPS_IMPORT is defined.

For instance see the toplevel CMakeLists.txt file in fips-glfw:

https://github.com/floooh/fips-glfw/blob/master/CMakeLists.txt

So the above fips-import CMakeLists.txt file would need to look like this:

if (NOT FIPS_IMPORT)
    cmake_minimum_required(VERSION 2.8)
    get_filename_component(FIPS_ROOT_DIR "../fips" ABSOLUTE)
    include("${FIPS_ROOT_DIR}/cmake/fips.cmake")
    fips_setup()
    fips_project(fips-import)
endif()
fips_begin_lib(dummy)
fips_src(dummy)
fips_deps(glew)
fips_end_lib()
if (NOT FIPS_IMPORT)
    fips_finish()
endif()

I could hide part of this check inside fips_setup()/fips_finish(), but the problem remains with the cmake_minim_required() call and including fips itself... but I will keep this ticket open as a remainder that there should be a better solution...