Move .qubesbuilder file existence check earlier

Raise NoQubesBuilderFileError earlier, before checking version.
Otherwise if neither version nor .qubesbuilder files is present, it
resulted in wrong exception (ComponentError "Cannot determine version"
instead of NoQubesBuilderFileError).

qubesbuilder/component.py

@@ -219,16 +219,16 @@ def get_parameters(self, placeholders: dict = None):
         if self.is_plugin or not self.has_packages:
             return {}
 
-        placeholders = placeholders or {}
-        placeholders.update(
-            {"@VERSION@": self.get_version(), "@REL@": self.get_release()}
-        )
-
         if not build_file.exists():
             raise NoQubesBuilderFileError(
                 f"Cannot find '.qubesbuilder' in {self.source_dir}."
             )
 
+        placeholders = placeholders or {}
+        placeholders.update(
+            {"@VERSION@": self.get_version(), "@REL@": self.get_release()}
+        )
+
         with open(build_file) as f:
             data = f.read()
 

tests/test_objects.py

@@ -117,6 +117,8 @@ def test_component_no_source():
 
 def test_component_no_version():
     with tempfile.TemporaryDirectory() as source_dir:
+        with open(f"{source_dir}/.qubesbuilder", "w"):
+            pass
         with pytest.raises(ComponentError) as e:
             QubesComponent(source_dir).get_parameters()
         msg = f"Cannot determine version for {source_dir}."
@@ -125,6 +127,8 @@ def test_component_no_version():
 
 def test_component_invalid_version():
     with tempfile.TemporaryDirectory() as source_dir:
+        with open(f"{source_dir}/.qubesbuilder", "w"):
+            pass
         with open(f"{source_dir}/version", "w") as f:
             f.write("wrongversion")
         with pytest.raises(ComponentError) as e:
@@ -147,6 +151,8 @@ def test_component_no_release():
 
 def test_component_invalid_release():
     with tempfile.TemporaryDirectory() as source_dir:
+        with open(f"{source_dir}/.qubesbuilder", "w"):
+            pass
         with open(f"{source_dir}/version", "w") as f:
             f.write("1.2.3")
         with open(f"{source_dir}/rel", "w") as f:
@@ -159,6 +165,8 @@ def test_component_invalid_release():
 
 def test_component_invalid_release2():
     with tempfile.TemporaryDirectory() as source_dir:
+        with open(f"{source_dir}/.qubesbuilder", "w"):
+            pass
         with open(f"{source_dir}/version", "w") as f:
             f.write("1.2.3")
         with open(f"{source_dir}/rel", "w") as f: