fix: Zmodel linker doesn't recursively visit base types when building resolution scopes

packages/schema/src/language-server/zmodel-linker.ts

@@ -519,12 +519,17 @@ export class ZModelLinker extends DefaultLinker {
 
     private resolveDataModel(node: DataModel, document: LangiumDocument<AstNode>, extraScopes: ScopeProvider[]) {
         if (node.superTypes.length > 0) {
-            const providers = node.superTypes.map(
-                (superType) => (name: string) => superType.ref?.fields.find((f) => f.name === name)
-            );
-            extraScopes = [...providers, ...extraScopes];
+            const superTypeProviders: ScopeProvider[] = [];
+            // build scope providers for super types recursively with breadth-first search
+            const queue = node.superTypes.map((t) => t.ref!);
+            while (queue.length > 0) {
+                const superType = queue.shift()!;
+                const provider = (name: string) => superType.fields.find((f) => f.name === name);
+                superTypeProviders.push(provider);
+                queue.push(...superType.superTypes.map((t) => t.ref!));
+            }
+            extraScopes = [...superTypeProviders, ...extraScopes];
         }
-
         return this.resolveDefault(node, document, extraScopes);
     }
 

tests/integration/tests/regression/issue-971.test.ts

@@ -0,0 +1,23 @@
+import { loadSchema } from '@zenstackhq/testtools';
+
+describe('Regression: issue 971', () => {
+    it('regression', async () => {
+        await loadSchema(
+            `
+            abstract model Level1 {
+                id String @id @default(cuid())
+                URL String?
+                @@validate(URL != null, "URL must be provided") // works
+            }
+            abstract model Level2 extends Level1 {
+                @@validate(URL != null, "URL must be provided") // works 
+            }
+            abstract model Level3 extends Level2 {
+                @@validate(URL != null, "URL must be provided") // doesn't work
+            }
+            model Foo extends Level3 {
+            }
+            `
+        );
+    });
+});