ament_pack_build_configuration is very slow for many dependencies

[Aposhian]

When targets with many dependencies call ament_target_dependencies, this calls ament_deduplicate_libraries and then ament_pack_build_configuration. For some reason ament_pack_build_configuration takes several seconds for a moderate number of libraries.

For two libraries, it takes 250ms (which is still kind of slow), but this ends up being the minority of the work done under ament_target_dependencies:

However, when you have 3632 dependencies (which seems like a lot but which is mostly separate type support libraries just from linking to Nav2) it takes 1.2 seconds. which then becomes the majority of the time of ament_target_dependencies

It looks like the bulk of that time comes from all the calls to

list(GET _argn ${_index} _lib)

for every single element, and that access takes 0.315ms, but that addes up over a lot of dependencies.

When building packages, this adds several seconds to the build time, just to add semicolons between library names.

This is on humble with ament_cmake 1.3.5.

[Aposhian]

Another example: here is a build of nav2_behavior_tree. You can see that the majority of the time in CMake build time ends up being due to this call, repeated many times for multiple targets:

[sloretz]

Does replacing ament_target_dependencies() with target_link_libraries() #292 resolve the issue?

[Aposhian]

Yes

[VRichardJP]

See #447 (comment) and #448