feat(stackable-versioned): Add new changed() validation

This throws an error if both from_name and from_type are
unset which suggests this action is not needed.

Author: Techassi

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

@@ -221,8 +221,14 @@ impl CommonItemAttributes {
     fn validate_changed_action(&self, item_ident: &impl ItemIdentExt) -> Result<()> {
         let mut errors = Error::accumulator();
 
-        // This ensures that `from_name` doesn't include the deprecation prefix.
         for change in &self.changes {
+            if change.from_name.is_none() && change.from_type.is_none() {
+                errors.push(Error::custom(
+                    "both `from_name` and `from_type` are unset. Is this `changed()` action needed?"
+                ).with_span(&change.since.span()));
+            }
+
+            // This ensures that `from_name` doesn't include the deprecation prefix.
             if let Some(from_name) = change.from_name.as_ref() {
                 if from_name.starts_with(item_ident.deprecated_prefix()) {
                     errors.push(
@@ -447,10 +453,6 @@ fn default_default_fn() -> SpannedValue<Path> {
     )
 }
 
-// TODO (@Techassi): Add validation for when from_name AND from_type are both
-// none => is this action needed in the first place?
-// TODO (@Techassi): Add validation that the from_name mustn't include the
-// deprecated prefix.
 /// For the changed() action
 ///
 /// Example usage:

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

@@ -4,12 +4,14 @@ fn main() {
     #[versioned(
         version(name = "v1alpha1"),
         version(name = "v1beta1"),
-        version(name = "v1")
+        version(name = "v1"),
+        version(name = "v2")
     )]
     struct Foo {
         #[versioned(
             changed(since = "v1beta1", from_name = "deprecated_bar"),
-            changed(since = "v1", from_name = "deprecated_baz")
+            changed(since = "v1", from_name = "deprecated_baz"),
+            changed(since = "v2")
         )]
         bar: usize,
     }