[Butakus]

Hi, it seems the Qt5/Qt6 issue is never resolved...

On Ubuntu 24.04, navmap_rviz_plugin fails to configure when the Qt6 development files are installed:

CMake Error at /opt/ros/rolling/share/rviz_common/cmake/ament_cmake_export_dependencies-extras.cmake:21 (find_package):
  Found package configuration file:
    /usr/lib/x86_64-linux-gnu/cmake/Qt5/Qt5Config.cmake
  but it set Qt5_FOUND to FALSE so package "Qt5" is considered to be NOT FOUND.
  Reason given by package:
  The Qt5 package requires at least one component

rviz_common 15.2.2 is built against Qt5, but its rviz_common-extras.cmake looks for Qt6 first and only falls back to Qt5 if Qt6 is missing. With Qt6 installed, Qt5 is never loaded, and the exported-dependencies step then runs a bare find_package(Qt5), which fails.

The existing Qt detection that we have in the CMakeLists.txt for the plugin (get_target_property on rviz_common::rviz_common) runs after find_package(rviz_common), so CMake never reaches it. CMake aborts with an error when calling find_package(rviz_common).

Fix

Before find_package(rviz_common), read rviz_common's exported dependencies to work out whether it uses Qt5 or Qt6:

• set qt_major, which is used for find_package(Qt${qt_major} ...) and linking, as before;
• when rviz uses Qt5, set CMAKE_DISABLE_FIND_PACKAGE_Qt6 so rviz's extras don't pick up Qt6.

[fmrico]

Thanks, the diagnosis is right: a Qt5 rviz_common (Kilted and older) looks for Qt6 first in its extras, so with Qt6 installed Qt5 is never loaded, and the old get_target_property check came after find_package(rviz_common), too late. Reading the exported dependencies first, and disabling Qt6 when rviz uses Qt5, follows rviz's own Qt as we want.

CI only builds on Rolling (Qt6), so I checked the Qt5 side in Docker (ros:kilted-ros-base and ros:jazzy-ros-base, with qt6-base-dev installed):

• With the released rviz_common (Kilted 15.0.15, Jazzy 14.1.24) the extras ask for Qt5 directly, so both rolling and this PR build: the PR does not break the released distros.
• With the Qt6-first extras of rviz_common 15.2.x (patched into Kilted's install), rolling fails with exactly the error in the description, and this PR builds; the plugin links only libQt5Core, libQt5Gui and libQt5Widgets.

Besides the inline comments:

• Minor: find_file caches RVIZ_COMMON_DEPS_FILE, so a build directory reused with another distro keeps the old path. Unlikely with colcon (one build dir per distro), just noting it.

[fmrico]

If AMENT_PREFIX_PATH is not set or does not contain rviz_common (e.g. a build that only passes CMAKE_PREFIX_PATH), find_file gives RVIZ_COMMON_DEPS_FILE-NOTFOUND and file(READ) aborts the configure with "failed to open for reading", which does not say what is wrong. Before this change that case worked.

Could it also search CMAKE_PREFIX_PATH, and when the file is not found skip the read and keep the previous detection (get_target_property on rviz_common::rviz_common after find_package(rviz_common))? Something like:

find_file(RVIZ_COMMON_DEPS_FILE ament_cmake_export_dependencies-extras.cmake
  PATHS ENV AMENT_PREFIX_PATH ${CMAKE_PREFIX_PATH}
  PATH_SUFFIXES share/rviz_common/cmake NO_DEFAULT_PATH)
if(RVIZ_COMMON_DEPS_FILE)
  ...
endif()

[Butakus]

See this comment for the description of the fix. I also added a NO_CACHE just in case a build directory is reused with another distro.

[Butakus]

Thanks for the review and for the extra testing with the containers!

I think these changes should cover everything to make the find more robust:

1. rviz_common not found: find_file now searches CMAKE_PREFIX_PATH first and then AMENT_PREFIX_PATH, the same order find_package uses. If the file still isn't found, configure stops with a clear FATAL_ERROR instead of the file(READ) error.
   I didn't add the get_target_property fallback: without AMENT_PREFIX_PATH the build already fails at find_package(rclcpp) (No 'rosidl_typesupport_c' found), before and after this PR. The case it would cover is an rviz_common reached only through rviz_common_DIR or PATH. Searching CMAKE_PREFIX_PATH first also stops us reading a different rviz_common than the one find_package uses, when two are installed.
2. Qt6 match: now matches only the list item: MATCHES "[\";]Qt6[\";]".
3. Cached path: added NO_CACHE to find_file, so a reused build directory doesn't keep an old path.

[fmrico]

Thanks @Butakus

Merging 🚀