Make sure to build_export_depend liblz4-dev.

[clalancette]

Otherwise downstream packages that depend on it won't install the package, and thus won't find the library.

@MichaelOrlov We need to break the freeze and land this on rolling so we can get mcap_vendor building on Rolling.

[clalancette]

CI:

• Linux
• Linux-aarch64
• Windows

[cottsay]

+1 for freeze exception - this is a very safe bugfix

[MichaelOrlov]

@clalancette @cottsay We can export dependencies from the liblz4-dev but it is not going to help with CI build failure.
The problem is not in the missing export of the dependencies but rather that header lz4.h is not found because libz4-dev is not installed by default.
At least on my local setup I am getting the following error even after the proposed fix:

--- stderr: liblz4_vendor
CMake Error at cmake/Modules/Findlz4.cmake:21 (file):
  file STRINGS file "/usr/include/lz4.h" cannot be read.
Call Stack (most recent call first):
  CMakeLists.txt:10 (find_package)

What it helps is to install liblz4-dev via sudo apt install liblz4-dev.

IMO instead of trying to refer to the lz4.h from the liblz4-dev we need to instruct CMake somehow to refer to the downloaded version of the lz4.h from the https://github.com/lz4/lz4/blob/dev/lib/lz4.h which we are vendoring.
It seems ament_vendor doesn't do a good job for that.

[MichaelOrlov]

@clalancette @cottsay BTW if needs a quick fix
Commenting out find_package(lz4 QUIET)

rosbag2/liblz4_vendor/CMakeLists.txt

Line 10 in 53570fa

find_package(lz4 QUIET)

will help.

[MichaelOrlov]

Sorry for my previous messages. You can disregard them. I didn't look at the original error messages from the failed job, and it turns out that they differ from my local setup reproduction.
The original one from the failed job https://build.ros2.org/job/Rbin_uN64__mcap_vendor__ubuntu_noble_amd64__binary/12/console

13:46:16 -- Found liblz4_vendor: 0.26.0 (/opt/ros/rolling/share/liblz4_vendor/cmake)
13:46:16 CMake Error at /usr/share/cmake-3.28/Modules/FindPackageHandleStandardArgs.cmake:230 (message):
13:46:16   Could NOT find lz4 (missing: lz4_LIBRARY lz4_INCLUDE_DIR)
13:46:16 Call Stack (most recent call first):
13:46:16   /usr/share/cmake-3.28/Modules/FindPackageHandleStandardArgs.cmake:600 (_FPHSA_FAILURE_MESSAGE)
13:46:16   /opt/ros/rolling/share/liblz4_vendor/cmake/Modules/Findlz4.cmake:36 (find_package_handle_standard_args)
13:46:16   CMakeLists.txt:7 (find_package)
13:46:16 

It seems the failure on my local setup is different and somehow Findlz4.cmake found a path for lz4 in my usr/include/ folder in the
find_path(lz4_INCLUDE_DIR NAMES lz4.h PATH_SUFFIXES "lz4" ${lz4_INCLUDE_PATH}) statement but there are no lz4.h file there.

[MichaelOrlov]

Approve