cmake --find-package ... -DNAME=drake does not work?

[EricCousineau-TRI]

When trying out different solutions for #7889, I wanted to see if I could get the include paths + flags for Drake "for free" using CMake in pkg-config mode:

# Downloaded and unpackaged a nightly here.
$ cat ./share/doc/drake/VERSION.TXT
20200729064618 2daabfac1b81f9165d8fece7891df03bb67e8e72
$ cmake --version
cmake version 3.10.2
$ cmake --find-package -DCMAKE_PREFIX_PATH=${PWD} -DNAME=drake -DCOMPILER_ID=GNU -DLANGUAGE=CXX -DMODE=COMPILE
CMake Error in lib/cmake/drake/drake-config.cmake:
  cmake_policy PUSH without matching POP
Call Stack (most recent call first):
  /usr/share/cmake-3.10/Modules/CMakeFindPackageMode.cmake:180 (find_package)

drake not found.
CMake Error: Problem processing arguments. Aborting.

FTR, there is a corresponding POP in the cps-generated drake-config.cmake file:
https://gist.github.com/EricCousineau-TRI/2567b4077d40cb2c85767d9981d078a8

FYI @jwnimmer-tri

[EricCousineau-TRI]

Tried with a later version of CMake, same result:

$ fhs-extend ~/.local/opt/cmake-3.18.0-rc4-Linux-x86_64/
$ cmake --version
cmake version 3.18.0-rc4
$ cmake --find-package -DCMAKE_PREFIX_PATH=${PWD} -DNAME=drake -DCOMPILER_ID=GNU -DLANGUAGE=C -DMODE=COMPILE
CMake Error in lib/cmake/drake/drake-config.cmake:
  cmake_policy PUSH without matching POP
Call Stack (most recent call first):
  /home/eacousineau/.local/opt/cmake-3.18.0-rc4-Linux-x86_64/share/cmake-3.18/Modules/CMakeFindPackageMode.cmake:183 (find_package)

[EricCousineau-TRI]

This failure mode doesn't seem relevant, but perhaps pycps can have an option to not put in cmake_policy()?
https://gitlab.kitware.com/cmake/cmake/-/issues/17612

EDIT: Actually, removing the cmake_policy bits does nothing.

So something else is broken, but it's unclear what.
FTR, I am able to configure drake-cmake-installed with that setup.

[jamiesnape]

cmake --find-package has probably always been broken, as it is on most CMake projects: https://cmake.org/cmake/help/latest/manual/cmake.1.html#run-the-find-package-tool. Not something we will fix.

[EricCousineau-TRI]

That's kinda buried. If it's not well supported, I think y'all should hoist that message even higher.

For example, on this semi-bleeding edge cmake version:

$ cmake --version
cmake version 3.18.0-rc4
$ cmake --help | grep '\--find-package' -C 1
  -P <file>                    = Process script mode.
  --find-package               = Run in pkg-config like mode.
  --graphviz=[file]            = Generate graphviz of dependencies, see

IMO, it should read:

  --find-package               = (UNSUPPORTED) Run in pkg-config like mode. Please avoid using this.

Can you please file the appropriate upstream issue, and then post it here and re-close this issue once you've done that?

[jamiesnape]

You are welcome to file the issue, but I think it is fine.

[jwnimmer-tri]

This is not a Drake-specific issue, so I don't see any need to keep this ticket open on the component: build system dashboard, or spend Drake's dime on it.

[EricCousineau-TRI]

Filed: https://gitlab.kitware.com/cmake/cmake/-/issues/21056