fix(domain): make FieldType::from_parts a strict inverse; reject stray bindings

crates/domain/src/field_definition.rs

@@ -10,8 +10,14 @@ pub enum FieldType {
     Integer,
     Date,
     Boolean,
-    Term { vocabulary_id: VocabularyId },
-    Authority { kind: Option<AuthorityKind> },
+    Term {
+        vocabulary_id: VocabularyId,
+    },
+    /// An authority reference. `kind: None` accepts any authority kind;
+    /// `Some(kind)` constrains to that kind.
+    Authority {
+        kind: Option<AuthorityKind>,
+    },
 }
 
 impl FieldType {
@@ -37,21 +43,30 @@ impl FieldType {
         }
     }
 
-    /// Reconstruct from the stored columns. `None` for an unknown or inconsistent combo
-    /// (e.g. `term` without a vocabulary).
+    /// Reconstruct from the stored columns. Returns `None` for an unknown
+    /// discriminant or an inconsistent combination — a scalar type carrying any
+    /// binding, a `term` without a vocabulary (or with an authority kind), or an
+    /// `authority` carrying a vocabulary.
     pub fn from_parts(
         data_type: &str,
         vocabulary_id: Option<VocabularyId>,
         authority_kind: Option<AuthorityKind>,
     ) -> Option<Self> {
+        let scalar = vocabulary_id.is_none() && authority_kind.is_none();
+
         match data_type {
-            "text" => Some(FieldType::Text),
-            "localized_text" => Some(FieldType::LocalizedText),
-            "integer" => Some(FieldType::Integer),
-            "date" => Some(FieldType::Date),
-            "boolean" => Some(FieldType::Boolean),
-            "term" => vocabulary_id.map(|vocabulary_id| FieldType::Term { vocabulary_id }),
-            "authority" => Some(FieldType::Authority {
+            "text" if scalar => Some(FieldType::Text),
+            "localized_text" if scalar => Some(FieldType::LocalizedText),
+            "integer" if scalar => Some(FieldType::Integer),
+            "date" if scalar => Some(FieldType::Date),
+            "boolean" if scalar => Some(FieldType::Boolean),
+            "term" => match vocabulary_id {
+                Some(vocabulary_id) if authority_kind.is_none() => {
+                    Some(FieldType::Term { vocabulary_id })
+                }
+                _ => None,
+            },
+            "authority" if vocabulary_id.is_none() => Some(FieldType::Authority {
                 kind: authority_kind,
             }),
             _ => None,
@@ -117,4 +132,24 @@ mod tests {
     fn unknown_type_is_none() {
         assert_eq!(FieldType::from_parts("blob", None, None), None);
     }
+
+    #[test]
+    fn stray_binding_on_scalar_type_is_rejected() {
+        let v = VocabularyId::new();
+        assert_eq!(FieldType::from_parts("text", Some(v), None), None);
+        assert_eq!(
+            FieldType::from_parts("boolean", None, Some(AuthorityKind::Person)),
+            None
+        );
+    }
+
+    #[test]
+    fn term_or_authority_with_wrong_binding_is_rejected() {
+        let v = VocabularyId::new();
+        assert_eq!(
+            FieldType::from_parts("term", Some(v), Some(AuthorityKind::Person)),
+            None
+        );
+        assert_eq!(FieldType::from_parts("authority", Some(v), None), None);
+    }
 }