feat: Emit error when both from_name and from_type are empty

Author: Techassi

crates/stackable-versioned-macros/src/attrs/common/item.rs

@@ -143,20 +143,20 @@ impl ItemAttributes {
 
         let mut errors = Error::accumulator();
 
-        // Semantic validation
+        // Common validation
         errors.handle(self.validate_action_combinations(item_ident, item_type));
         errors.handle(self.validate_action_order(item_ident, item_type));
         errors.handle(self.validate_item_name(item_ident, item_type));
-        errors.handle(self.validate_changed_item_name(item_type));
         errors.handle(self.validate_item_attributes(item_attrs));
 
+        // Action specific validation
+        errors.handle(self.validate_changed_action(item_ident, item_type));
+
         // TODO (@Techassi): Add hint if a field or variant is added in the
         // first version that it might be clever to remove the 'added'
         // attribute.
 
-        errors.finish()?;
-
-        Ok(())
+        errors.finish()
     }
 
     /// This associated function is called by the top-level validation function
@@ -293,22 +293,35 @@ impl ItemAttributes {
                 }
             }
         }
+
         Ok(())
     }
 
     /// This associated function is called by the top-level validation function
     /// and validates that parameters provided to the `changed` actions are
     /// valid.
-    fn validate_changed_item_name(&self, item_type: &ItemType) -> Result<(), Error> {
+    fn validate_changed_action(
+        &self,
+        item_ident: &Ident,
+        item_type: &ItemType,
+    ) -> Result<(), Error> {
         let prefix = match item_type {
             ItemType::Field => DEPRECATED_FIELD_PREFIX,
             ItemType::Variant => DEPRECATED_VARIANT_PREFIX,
         };
 
         let mut errors = Error::accumulator();
 
-        // This ensures that `from_name` doesn't include the deprecation prefix.
         for change in &self.changes {
+            // Ensure that from_name and from_type are not empty at the same
+            // time.
+            if change.from_name.is_none() && change.from_type.is_none() {
+                errors.push(Error::custom(format!(
+                    "{item_type} was marked as `changed`, but both `from_name` and `from_type` are unset"
+                )).with_span(item_ident));
+            }
+
+            // Ensure that `from_name` doesn't include the deprecation prefix.
             if let Some(from_name) = change.from_name.as_ref() {
                 if from_name.starts_with(prefix) {
                     errors.push(

crates/stackable-versioned-macros/tests/default/fail/changed.rs

@@ -9,7 +9,7 @@ fn main() {
     struct Foo {
         #[versioned(
             changed(since = "v1beta1", from_name = "deprecated_bar"),
-            changed(since = "v1", from_name = "deprecated_baz")
+            changed(since = "v1")
         )]
         bar: usize,
     }

crates/stackable-versioned-macros/tests/default/fail/changed.stderr

@@ -4,8 +4,8 @@ error: the previous field name must not start with the deprecation prefix
 11 |             changed(since = "v1beta1", from_name = "deprecated_bar"),
    |                                                    ^^^^^^^^^^^^^^^^
 
-error: the previous field name must not start with the deprecation prefix
-  --> tests/default/fail/changed.rs:12:47
+error: field was marked as `changed`, but both `from_name` and `from_type` are unset
+  --> tests/default/fail/changed.rs:14:9
    |
-12 |             changed(since = "v1", from_name = "deprecated_baz")
-   |                                               ^^^^^^^^^^^^^^^^
+14 |         bar: usize,
+   |         ^^^