Plugin import breaks if CMAKE_RUNTIME_OUTPUT_DIRECTORY_* is set

[Gollum999]

Environment

• Windows 10
• Visual Studio 16.8.2 (MSVC 19.28.29334)
• CMake 3.18.1
• Magnum 92d0609
• Corrade mosra/corrade@e5970c4

Problem

If CMAKE_RUNTIME_OUTPUT_DIRECTORY_<CONFIG> is set, trying to load plugins will fail. Example error message:

PluginManager::Manager::Manager(): none of the plugin search paths in {C:/code/magnum/bld/vs/Debug/bin/magnum-d/importers, magnum-d/importers} exists and pluginDirectory was not set, skipping plugin discovery
PluginManager::Manager::load(): plugin TgaImporter is not static and was not found in

As described here, if this variable is set, it is used to initialize the RUNTIME_OUTPUT_DIRECTORY_<CONFIG> property of each target. This property takes precedence over the RUNITME_OUPUT_DIRECTORY property. This means that the output directories that are set in each plugin's CMakeLists end up being overridden. This causes the plugin library to not be built into the expected location, causing it to fail to load at runtime.

To reproduce

Build Magnum as a subproject as in Example 1a of the Getting Started guide. Add the following lines to CMake before add_subdirectory(magnum):

set(CMAKE_RUNTIME_OUTPUT_DIRECTORY_DEBUG ${CMAKE_RUNTIME_OUTPUT_DIRECTORY})
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY_RELEASE ${CMAKE_RUNTIME_OUTPUT_DIRECTORY})

Then build with some plugin enabled and try to load the plugin at runtime.

[Gollum999]

Just as a note, in my case I ran into this because of Conan. By default, conan_basic_setup modifies the build output directories by setting these CMake variables. I switched to using conan_basic_setup(NO_OUTPUT_DIRS) to avoid this behavior.

[mosra]

Hi,

yeah, the plugins are expected to be in those particular subdirectories (magnum/blah) relative to the interface library, otherwise it's not really possible for the plugin manager to discover them or know which plugin is which. The library already decides based on presence / value of CMAKE_RUNTIME_OUTPUT_DIRECTORY on its own, but isn't currently aware of CMAKE_RUNTIME_OUTPUT_DIRECTORY_<CONFIG>.

I'll have to fix that.

[mosra]

This should be fixed with #570. Sorry it took half a century to get this done.