Let ModelProvider load modelProviders

Model providers do not need to be services.
They do not have behaviour, only provider data to other services.

gaphor/services/modelprovider.py

@@ -0,0 +1,51 @@
+from typing import Dict
+
+from gaphor.abc import ModelProvider, Service
+from gaphor.entrypoint import initialize
+
+
+class ModelProviderService(Service, ModelProvider):
+
+    DEFAULT_PROFILE = "UML"
+
+    def __init__(self, properties={}):
+        """
+        Create a new Model Provider. It will provide all models defined
+        as entrypoints under `[gaphor.modelproviders]`.
+
+        Te `properties` argument is optional, in which case the service will
+        default to UML.
+        """
+        self.model_providers: Dict[str, ModelProvider] = initialize(
+            "gaphor.modelproviders"
+        )
+        self.properties = properties
+
+    def shutdown(self):
+        pass
+
+    @property
+    def active_provider(self):
+        profile = self.properties.get("profile", default=self.DEFAULT_PROFILE)
+        if profile not in self.model_providers:
+            profile = self.DEFAULT_PROFILE
+        return self.model_providers[profile]
+
+    @property
+    def name(self):
+        return self.active_provider.name
+
+    def lookup_element(self, name):
+        return self.first(lambda provider: provider.lookup_element(name))
+
+    def lookup_diagram_item(self, name):
+        return self.first(lambda provider: provider.lookup_diagram_item(name))
+
+    def toolbox_definition(self):
+        return self.active_provider.toolbox_definition
+
+    def first(self, predicate):
+        for _, provider in self.model_providers.items():
+            type = predicate(provider)
+            if type:
+                return type

gaphor/services/tests/test_modelprovider.py

@@ -0,0 +1,7 @@
+from gaphor.services.modelprovider import ModelProviderService
+
+
+def test_loading_of_model_providers():
+    model_provider = ModelProviderService(properties={})
+
+    assert "UML" in model_provider.model_providers

pyproject.toml

@@ -71,7 +71,7 @@ gaphorconvert = 'gaphor.tools.gaphorconvert:main'
 "properties" = "gaphor.services.properties:Properties"
 "undo_manager" = "gaphor.services.undomanager:UndoManager"
 "element_factory" = "gaphor.core.modeling:ElementFactory"
-"model_provider" = "gaphor.UML.modelprovider:UMLModelProvider"
+"model_provider" = "gaphor.services.modelprovider:ModelProviderService"
 "uml_model_provider" = "gaphor.UML.modelprovider:UMLModelProvider"
 "file_manager" = "gaphor.ui.filemanager:FileManager"
 "recent_files" = "gaphor.ui.recentfiles:RecentFiles"
@@ -89,6 +89,9 @@ gaphorconvert = 'gaphor.tools.gaphorconvert:main'
 "diagram_export" = "gaphor.plugins.diagramexport:DiagramExport"
 "xmi_export" = "gaphor.plugins.xmiexport:XMIExport"
 
+[tool.poetry.plugins."gaphor.modelproviders"]
+"UML" = "gaphor.UML.modelprovider:UMLModelProvider"
+
 [tool.isort]
 multi_line_output = 3
 include_trailing_comma = true