fix: disallow extending from multiple delegate models

packages/schema/src/language-server/validator/datamodel-validator.ts

@@ -22,6 +22,7 @@ import { validateDuplicatedDeclarations } from './utils';
 export default class DataModelValidator implements AstValidator<DataModel> {
     validate(dm: DataModel, accept: ValidationAcceptor): void {
         this.validateBaseAbstractModel(dm, accept);
+        this.validateBaseDelegateModel(dm, accept);
         validateDuplicatedDeclarations(dm, getModelFieldsWithBases(dm), accept);
         this.validateAttributes(dm, accept);
         this.validateFields(dm, accept);
@@ -396,6 +397,15 @@ export default class DataModelValidator implements AstValidator<DataModel> {
                 );
         });
     }
+
+    private validateBaseDelegateModel(model: DataModel, accept: ValidationAcceptor) {
+        if (model.superTypes.filter((base) => base.ref && isDelegateModel(base.ref)).length > 1) {
+            accept('error', 'Extending from multiple delegate models is not supported', {
+                node: model,
+                property: 'superTypes',
+            });
+        }
+    }
 }
 
 export interface MissingOppositeRelationData {

packages/schema/tests/schema/validation/datamodel-validation.test.ts

@@ -714,4 +714,28 @@ describe('Data Model Validation Tests', () => {
             errorLike(`The relation field "user" on model "A" is missing an opposite relation field on model "User"`)
         );
     });
+
+    it('delegate base type', async () => {
+        const errors = await safelyLoadModel(`
+                    ${prelude}
+
+                    model Base1 {
+                        id String @id
+                        type String
+                        @@delegate(type)
+                    }
+
+                    model Base2 {
+                        id String @id
+                        type String
+                        @@delegate(type)
+                    }
+
+                    model A extends Base1,Base2 {
+                        a String
+                    }
+                `);
+
+        expect(errors).toMatchObject(errorLike(`Extending from multiple delegate models is not supported`));
+    });
 });