fix: more robust determination of the app version

Instead of default to the installed metadata, first try to use the app's
main package (via the standard __version__ attribute), *then* fallback
to importlib.metadata, *then* fallback to "dev".

Fixes #90

craft_application/application.py

@@ -18,6 +18,7 @@
 
 import argparse
 import functools
+import importlib
 import os
 import pathlib
 import signal
@@ -67,7 +68,20 @@ class AppMetadata:
 
     def __post_init__(self) -> None:
         setter = super().__setattr__
-        setter("version", metadata.version(self.name))
+
+        # Try to determine the app version.
+        try:
+            # First, via the __version__ attribute on the app's main package.
+            version = importlib.import_module(self.name).__version__
+        except (AttributeError, ModuleNotFoundError):
+            try:
+                # If that fails, try via the installed metadata.
+                version = metadata.version(self.name)
+            except metadata.PackageNotFoundError:
+                # If that fails too, default to "dev".
+                version = "dev"
+
+        setter("version", version)
         if self.summary is None:
             md = metadata.metadata(self.name)
             setter("summary", md["summary"])

tests/unit/test_application.py

@@ -15,6 +15,8 @@
 # with this program.  If not, see <http://www.gnu.org/licenses/>.
 """Unit tests for craft-application app classes."""
 import argparse
+import importlib
+import importlib.metadata
 import pathlib
 import re
 import subprocess
@@ -46,6 +48,31 @@ def test_app_metadata_post_init_correct(summary):
     pytest_check.is_not_none(app.summary)
 
 
+def test_app_metadata_version_attribute(tmp_path, monkeypatch):
+    """Set the AppMetadata version from the main app package."""
+    monkeypatch.syspath_prepend(tmp_path)
+    (tmp_path / "dummycraft_version.py").write_text("__version__ = '1.2.3'")
+
+    app = application.AppMetadata(name="dummycraft_version", summary="dummy craft")
+    assert app.version == "1.2.3"
+
+
+def test_app_metadata_importlib(tmp_path, monkeypatch, mocker):
+    """Set the AppMetadata version via importlib."""
+    monkeypatch.syspath_prepend(tmp_path)
+    (tmp_path / "dummycraft_importlib.py").write_text("print('hi')")
+
+    mocker.patch.object(importlib.metadata, "version", return_value="4.5.6")
+
+    app = application.AppMetadata(name="dummycraft_importlib", summary="dummy craft")
+    assert app.version == "4.5.6"
+
+
+def test_app_metadata_dev():
+    app = application.AppMetadata(name="dummycraft_dev", summary="dummy craft")
+    assert app.version == "dev"
+
+
 @pytest.fixture()
 def app(app_metadata, fake_services):
     return application.Application(app_metadata, fake_services)