Fix/revisit get_package

src/towncrier/_project.py

@@ -16,26 +16,22 @@
 
 def _get_package(package_dir, package):
 
-    # Step 1: Try the dumbest and simplest thing that could possibly work.
-    # Yes, that means importing it. Call the cops, I don't care.
-
-    sys.path.insert(1, package_dir)
-
     try:
         module = import_module(package)
-    except ImportError as e:
-        print("Tried to import {}, but ran into this error: {}".format(package, e))
-        # wups that didn't work
-        module = None
-
-    # Don't leave trash in sys.path
-    sys.path.pop(0)
-
-    # Step 2: uhhhhhhh
-    # TBA
-
-    if not module:
-        raise Exception("Can't find your project :(")
+    except ImportError:
+        # Package is not already available / installed.
+        # Force importing it based on the source files.
+        sys.path.insert(0, package_dir)
+
+        try:
+            module = import_module(package)
+        except ImportError as e:
+            err = "tried to import {}, but ran into this error: {}".format(package, e)
+            # NOTE: this might be redirected via "towncrier --draft > …".
+            print("ERROR: {}".format(err))
+            raise
+        finally:
+            sys.path.pop(0)
 
     return module
 

src/towncrier/newsfragments/297.feature.rst

@@ -0,0 +1,2 @@
+When searching for the project, first check for an existing importable instance.
+This helps if the version is only available in the installed version and not the source.

src/towncrier/test/test_project.py

@@ -39,6 +39,66 @@ def test_tuple(self):
         version = get_version(temp, "mytestproja")
         self.assertEqual(version, "1.3.12")
 
+    def test_import_fails(self):
+        """
+        An exception is raised when getting the version failed due to missing Python package files.
+        """
+        if sys.version_info >= (3, 6):
+            expected_exception = ModuleNotFoundError
+        else:
+            expected_exception = ImportError
+
+        with self.assertRaises(expected_exception):
+            get_version(".", "projectname_without_any_files")
+
+    def test_already_installed_import(self):
+        """
+        An already installed package will be checked before cwd-found packages.
+        """
+        project_name = "mytestproj_already_installed_import"
+
+        temp = self.mktemp()
+        os.makedirs(temp)
+        os.makedirs(os.path.join(temp, project_name))
+
+        with open(os.path.join(temp, project_name, "__init__.py"), "w") as f:
+            f.write("__version__ = (1, 3, 12)")
+
+        sys_path_temp = self.mktemp()
+        os.makedirs(sys_path_temp)
+        os.makedirs(os.path.join(sys_path_temp, project_name))
+
+        with open(os.path.join(sys_path_temp, project_name, "__init__.py"), "w") as f:
+            f.write("__version__ = (2, 1, 5)")
+
+        sys.path.insert(0, sys_path_temp)
+        self.addCleanup(sys.path.pop, 0)
+
+        version = get_version(temp, project_name)
+
+        self.assertEqual(version, "2.1.5")
+
+    def test_installed_package_found_when_no_source_present(self):
+        """
+        The version from the installed package is returned when there is no
+        package present at the provided source directory.
+        """
+        project_name = "mytestproj_only_installed"
+
+        sys_path_temp = self.mktemp()
+        os.makedirs(sys_path_temp)
+        os.makedirs(os.path.join(sys_path_temp, project_name))
+
+        with open(os.path.join(sys_path_temp, project_name, "__init__.py"), "w") as f:
+            f.write("__version__ = (3, 14)")
+
+        sys.path.insert(0, sys_path_temp)
+        self.addCleanup(sys.path.pop, 0)
+
+        version = get_version("some non-existent directory", project_name)
+
+        self.assertEqual(version, "3.14")
+
 
 class InvocationTests(TestCase):
     def test_dash_m(self):