Handle reusing a deleted version number in signing API (#19697)

Change the error message for version number conflict to no longer
reference the latest version, and instead align on what devhub
does.

src/olympia/signing/tests/test_views.py

@@ -191,9 +191,7 @@ class TestUploadVersion(BaseUploadVersionTestMixin, TestCase):
             'PUT', self.url(self.guid, '2.1.072'), version='2.1.072'
         )
         assert response.status_code == 409
-        assert response.data['error'] == (
-            'Version already exists. Latest version is: 2.1.072.'
-        )
+        assert response.data['error'] == ('Version 2.1.072 already exists.')
 
     @mock.patch('olympia.devhub.views.Version.from_upload')
     def test_no_version_yet(self, from_upload):
@@ -239,8 +237,18 @@ class TestUploadVersion(BaseUploadVersionTestMixin, TestCase):
 
         response = self.request('PUT', self.url(self.guid, '3.0'))
         assert response.status_code == 409
+        assert response.data['error'] == ('Version 3.0 already exists.')
+
+    def test_only_version_already_uploaded_was_deleted(self):
+        # Make the only version conflict with the version number we're about to
+        # upload, and soft-delete it.
+        Version.objects.filter(addon__guid=self.guid, version='2.1.072').update(
+            version='3.0', deleted=True
+        )
+        response = self.request('PUT', self.url(self.guid, '3.0'))
+        assert response.status_code == 409, response.data
         assert response.data['error'] == (
-            'Version already exists. Latest version is: 3.0.'
+            'Version 3.0 was uploaded before and deleted.'
         )
 
     def test_version_failed_review(self):
@@ -251,9 +259,7 @@ class TestUploadVersion(BaseUploadVersionTestMixin, TestCase):
 
         response = self.request('PUT', self.url(self.guid, '3.0'))
         assert response.status_code == 409
-        assert response.data['error'] == (
-            'Version already exists. Latest version is: 3.0.'
-        )
+        assert response.data['error'] == ('Version 3.0 already exists.')
 
         # Verify that you can check the status after upload (#953).
         response = self.get(self.url(self.guid, '3.0'))

src/olympia/signing/views.py

@@ -143,16 +143,18 @@ class VersionView(APIView):
                 status.HTTP_400_BAD_REQUEST,
             )
 
-        existing_version = addon and Version.unfiltered.filter(
-            addon=addon, version=version_string
+        existing_version = (
+            addon
+            and Version.unfiltered.filter(addon=addon, version=version_string).last()
         )
         if existing_version:
-            latest_version = addon.find_latest_version(None, exclude=())
-            msg = gettext(
-                'Version already exists. Latest version is: %s.'
-                % latest_version.version
+            if existing_version.deleted:
+                msg = gettext('Version {version} was uploaded before and deleted.')
+            else:
+                msg = gettext('Version {version} already exists.')
+            raise forms.ValidationError(
+                msg.format(version=version_string), status.HTTP_409_CONFLICT
             )
-            raise forms.ValidationError(msg, status.HTTP_409_CONFLICT)
 
         package_guid = parsed_data.get('guid', None)