How to manage the dependencies of custom Qt plugin (not for Qt Creator)?

Question

I've recently started working with plugins in Qt just for fun. One thing I still can't figure out is how to define and manage a plugin's dependencies on other plugins (and libraries). I'm using the Plug&Paint example .

When it comes to Qt Creator for instance there are two variables that handle this namely QTC_PLUGIN_DEPENDS (for being dependant on other plugins) and QTC_LIB_DEPENDS (for being dependant on specific libraries). As an example there is the VcsBase (version control system base plugin):

QTC_PLUGIN_NAME = VcsBase
QTC_LIB_DEPENDS += \  // <--------------------libraries the Qt Creator plugin depends on
    aggregation \
    cplusplus \
    extensionsystem \
    utils
QTC_PLUGIN_DEPENDS += \ //<-------------------other plugins the Qt Creator plugin depends on
    coreplugin \
    texteditor \
    projectexplorer \
    cpptools \
    diffeditor
QTC_PLUGIN_RECOMMENDS += \
cpaster

As you can see it has multiple library and plugin dependencies. From how I understand all this in the IDE all plugins have at least on other plugin dependency namely the coreplugin . In addition to that other plugins provide partial functionality to the plugin that depends on these.

To continue the example we have the Git , SVN etc. plugins all of which depend on VcsBase since all depend on functionality that this plugin offers.

I can look into these two variables but I have the feeling that there should be a better way than just sifting through the code of Qt Creator (not exactly beginner friendly). I checked QPluginLoader but the only thing connected to the term dependent is platform-independent , which is not what I'm looking for.

The "trivial" way would be to check all available plugins and then - based on a predefined loading order - check if plugin A and B are available so that the present plugin C (which depends on both) can be loaded. However this would mean that I need to add the dependencies to the core application. I do believe that this is something that each plugin needs to take care of on its own (more or less).

Answer 1

It seems that there is no direct way to do that. The only way I have found so far is through the JSON file that goes along with each plugin. There one can enter a key - let's call it "deps" - and call the meta data through QPluginLoader::metaData() . This function returns a QJsonObject (the root of the JSON document. One can then find "deps" and get the content (for example a list of names of other plugins, that the current one depends on). Next one can check if the mentioned dependencies are present and loaded and so on.