chore: 🤖 add support for nested attributes errors

addons/api/addon/adapters/application.js

@@ -263,14 +263,36 @@ export default class ApplicationAdapter extends RESTAdapter.extend(
       source: { pointer: '/data' },
     };
     // Normalize field-specific errors, if any.
-    const errors = fieldErrors.map((error) => ({
-      detail: error.description,
-      // Ember Data cannot handle errors on nested attributes, so these are
-      // flattened (e.g. `attributes.foobar` becomes `attributes_foobar`).
-      // To capture these errors, add read-only fields on the model
-      // corresponding to the underscored field name.
-      source: { pointer: `/data/attributes/${error.name.replace('.', '_')}` },
-    }));
+    const errors = fieldErrors.flatMap((error) => {
+      const newValue = [
+        {
+          detail: error.description,
+          // Ember Data cannot handle errors on nested attributes, so these are
+          // flattened (e.g. `attributes.foobar` becomes `attributes_foobar`).
+          // To capture these errors, add read-only fields on the model
+          // corresponding to the underscored field name.
+          source: {
+            pointer: `/data/attributes/${error.name.replace('.', '_')}`,
+          },
+        },
+      ];
+      if (error.name.includes('attributes.')) {
+        newValue.push({
+          detail: error.description,
+          // Going forward, nested attributes will be hoisted.  Thus "attributes."
+          // must be stripped from the error name key.  Until all models are
+          // transitioned away from model fragments, however, both this and the
+          // prior error key mappings are necessary.
+          source: {
+            pointer: `/data/attributes/${error.name.replace(
+              'attributes.',
+              ''
+            )}`,
+          },
+        });
+      }
+      return newValue;
+    });
     // Return a list of JSON API errors rooted under the `errors` key.
     return {
       errors: [baseError, ...errors],