python: raise an exception on plugin load/unload failure.

Because that makes sense. Returning some None doesn't.

doc/python/conf.py

@@ -117,6 +117,7 @@ INPUT_PAGES = [
 INPUT_DOCS = [
     'corrade.rst',
     'corrade.containers.rst',
+    'corrade.pluginmanager.rst',
 
     'magnum.rst',
     'magnum.gl.rst',

doc/python/corrade.pluginmanager.rst

@@ -0,0 +1,36 @@
+..
+    This file is part of Magnum.
+
+    Copyright © 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019
+              Vladimír Vondruš <mosra@centrum.cz>
+
+    Permission is hereby granted, free of charge, to any person obtaining a
+    copy of this software and associated documentation files (the "Software"),
+    to deal in the Software without restriction, including without limitation
+    the rights to use, copy, modify, merge, publish, distribute, sublicense,
+    and/or sell copies of the Software, and to permit persons to whom the
+    Software is furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included
+    in all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+    THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+    DEALINGS IN THE SOFTWARE.
+..
+
+.. py:class:: corrade.pluginmanager.AbstractManager
+    :data VERSION: Plugin ABI version
+
+.. py:function:: corrade.pluginmanager.AbstractManager.load
+    :raise RuntimeError: When loading fails
+    :return: `LoadState.LOADED`, possibly combined with other flags such as
+        `LoadState.STATIC`
+
+.. py:function:: corrade.pluginmanager.AbstractManager.unload
+    :raise RuntimeError: When unloading fails
+    :return: Either `LoadState.NOT_LOADED` or `LoadState.STATIC`

src/python/corrade/pluginmanager.cpp

@@ -63,8 +63,28 @@ void pluginmanager(py::module& m) {
         .def_property_readonly("alias_list", &PluginManager::AbstractManager::aliasList, "List of all available alias names")
         /** @todo metadata() (figure out the ownership) */
         .def("load_state", &PluginManager::AbstractManager::loadState, "Load state of a plugin")
-        .def("load", &PluginManager::AbstractManager::load, "Load a plugin")
-        .def("unload", &PluginManager::AbstractManager::unload, "Unload a plugin");
+        .def("load", [](PluginManager::AbstractManager& self, const std::string& plugin) {
+            /** @todo log redirection -- but we'd need assertions to not be
+                part of that so when it dies, the user can still see why */
+            const PluginManager::LoadState state = self.load(plugin);
+            if(!(state & PluginManager::LoadState::Loaded)) {
+                PyErr_Format(PyExc_RuntimeError, "can't load plugin %s", plugin.data());
+                throw py::error_already_set{};
+            }
+
+            return state;
+        }, "Load a plugin")
+        .def("unload", [](PluginManager::AbstractManager& self, const std::string& plugin) {
+            /** @todo log redirection -- but we'd need assertions to not be
+                part of that so when it dies, the user can still see why */
+            const PluginManager::LoadState state = self.unload(plugin);
+            if(state != PluginManager::LoadState::NotLoaded && state != PluginManager::LoadState::Static) {
+                PyErr_Format(PyExc_RuntimeError, "can't unload plugin %s", plugin.data());
+                throw py::error_already_set{};
+            }
+
+            return state;
+        }, "Unload a plugin");
 }
 
 }