1 files changed, 83 insertions, 0 deletions
diff --git a/src/buildstream/_pluginfactory/pluginoriginjunction.py b/src/buildstream/_pluginfactory/pluginoriginjunction.py
new file mode 100644
index 000000000..7c887e4cb
--- /dev/null
+++ b/src/buildstream/_pluginfactory/pluginoriginjunction.py
@@ -0,0 +1,83 @@
+#
+#  Copyright (C) 2020 Codethink Limited
+#
+#  This program is free software; you can redistribute it and/or
+#  modify it under the terms of the GNU Lesser General Public
+#  License as published by the Free Software Foundation; either
+#  version 2 of the License, or (at your option) any later version.
+#
+#  This library is distributed in the hope that it will be useful,
+#  but WITHOUT ANY WARRANTY; without even the implied warranty of
+#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
+#  Lesser General Public License for more details.
+#
+#  You should have received a copy of the GNU Lesser General Public
+#  License along with this library. If not, see <http://www.gnu.org/licenses/>.
+#
+from .._exceptions import PluginError
+
+from .pluginorigin import PluginType, PluginOrigin, PluginOriginType
+
+
+# PluginOriginJunction
+#
+# PluginOrigin for junction plugins
+#
+class PluginOriginJunction(PluginOrigin):
+    def __init__(self):
+        super().__init__(PluginOriginType.JUNCTION)
+
+        # The junction element name through which to load plugins
+        self._junction = None
+
+    def get_plugin_paths(self, kind, plugin_type):
+
+        # Get access to the project indicated by the junction,
+        # possibly loading it as a side effect.
+        #
+        loader = self.project.loader.get_loader(self._junction)
+        project = loader.project
+        project.ensure_fully_loaded()
+
+        # Now get the appropriate PluginFactory object
+        #
+        if plugin_type == PluginType.SOURCE:
+            factory = project.config.source_factory
+        elif plugin_type == PluginType.ELEMENT:
+            factory = project.config.element_factory
+
+        # Now ask for the paths from the subproject PluginFactory
+        try:
+            location, defaults = factory.get_plugin_paths(kind)
+        except PluginError as e:
+            # Add some context to an error raised by loading a plugin from a subproject
+            #
+            raise PluginError(
+                "{}: Error loading {} plugin '{}' from project '{}' referred to by junction '{}': {}".format(
+                    self.provenance, plugin_type, kind, project.name, self._junction, e
+                ),
+                reason="junction-plugin-load-error",
+                detail=e.detail,
+            ) from e
+
+        if not location:
+            # Raise a helpful error if the referred plugin type is not found in a subproject
+            #
+            # Note that this can also bubble up through the above error when looking for
+            # a plugin from a subproject which in turn requires the same plugin from it's
+            # subproject.
+            #
+            raise PluginError(
+                "{}: project '{}' referred to by junction '{}' does not declare any {} plugin kind: '{}'".format(
+                    self.provenance, project.name, self._junction, plugin_type, kind
+                ),
+                reason="junction-plugin-not-found",
+            )
+
+        return location, defaults
+
+    def load_config(self, origin_node):
+
+        origin_node.validate_keys(["junction", *PluginOrigin._COMMON_CONFIG_KEYS])
+
+        self._junction = origin_node.get_str("junction")