AMENT_PREFIX_PATH: Environment variable vs CMake variable

[furushchev]

I found the CMake variable AMENT_PREFIX_PATH is set in the following files in this repository:

bloom/bloom/generators/debian/templates/ament_cmake/rules.em

Line 36 in d3d21ae

-DAMENT_PREFIX_PATH="@(InstallationPrefix)" \

bloom/bloom/generators/rpm/templates/ament_cmake/template.spec.em

Line 49 in d3d21ae

-DAMENT_PREFIX_PATH="@(InstallationPrefix)" \

However, the variable is not assumed to be the CMake variable but the environment variable in the ament/ament_cmake repository.
for instance:
https://github.com/ament/ament_cmake/blob/dc576abb40986f9d1ce8e534eb17770a625014cd/ament_cmake_core/cmake/environment/ament_cmake_environment_package_hook.cmake#L33

I want to clarify if there is any background to have this variable set as the environment variable or if it just needs to be fixed.
(I'll make a PR if it's the latter case.)

[furushchev]

@cottsay Hi! Do you have any insights on this topic? (I mentioned you because the change above was committed by you)
0dc2646

[meetgandhi-dev]

@furushchev
I believe, you're correct.
Do you have a fix for the same?

[cottsay]

Hmm, I think these lines can be removed from the templates you referenced. From what I can tell, AMENT_PREFIX_PATH is only ever set and only ever used as an environment variable and never as a CMake variable. In this context, sourcing the setup scripts sets the variable appropriately.

We should survey the ROS 2 codebase to be absolutely sure nobody is relying on this variable being set in this way before merging a change to drop it.

Keep in mind that defining the variable shouldn't cause any misbehavior, it's just misleading.

@nuclearsandwich originally added the flag to the ament_cmake templates - do you have any context to add?