update: concatenate Arrays when target node is an array

src/overlay.js

@@ -22,9 +22,14 @@ function applyOverlayToOpenAPI(spec, overlay) {
 			try {
 				// It must be an update
 				jsonpath.apply(spec, a.target, (chunk) => {
-					// Deep merge using a module (built-in spread operator is only shallow)
-					const merger = mergician({appendArrays: true})
-					return merger(chunk, a.update)
+					if (Array.isArray(chunk) && Array.isArray(a.update)) {
+						// Concat arrays if target and update are both array objects
+						return chunk.concat(a.update);
+					} else {
+						// Deep merge objects using a module (built-in spread operator is only shallow)
+						const merger = mergician({ appendArrays: true });
+						return merger(chunk, a.update);
+					}
 				});
 			}
 			catch (ex) {

test/expected/town-update-array.yaml

@@ -0,0 +1,72 @@
+openapi: 3.1.0
+info:
+  version: 1.0.0
+  title: Imaginary town
+servers:
+  - url: 'https://example.com'
+    description: Example server
+  - url: 'https://example.com/prod'
+    description: Production server
+paths:
+  /buildings:
+    get:
+      summary: All buildings
+      operationId: buildingsList
+      responses:
+        '200':
+          description: Return all known buildings
+          content:
+            application/json:
+              schema:
+                type: array
+                items:
+                  $ref: '#/components/schemas/Building'
+  '/buildings/{buildingId}':
+    get:
+      summary: Specific building
+      operationId: buildingById
+      parameters:
+        - name: buildingId
+          in: path
+          required: true
+          description: Which building to return
+          schema:
+            type: string
+      responses:
+        '200':
+          description: Return a building
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Building'
+  /locations:
+    get:
+      summary: All locations
+      operationId: locationList
+      responses:
+        '200':
+          description: Returns all locations
+          content:
+            application/json:
+              schema:
+                type: array
+                items:
+                  type: object
+                  properties:
+                    location_id:
+                      type: integer
+                      example: 44
+                    name:
+                      type: string
+                      example: North Village
+components:
+  schemas:
+    Building:
+      type: object
+      properties:
+        building:
+          type: string
+          example: house
+        location_id:
+          type: integer
+          example: 44

test/overlay.test.js

@@ -59,6 +59,17 @@ test('remove all description fields', () => {
 	expect(result).toEqual(expectedOutput);
 });
 
+test('concatenate lists when target is an array type', () => {
+	const openapiFile = "test/openapi/town.yaml";
+	const overlayFile = "test/overlays/update-array.yaml";
+	const expectedFile = "test/expected/town-update-array.yaml";
+	const expectedOutput = fs.readFileSync(expectedFile, 'utf8');
+
+	const result = overlayFiles(openapiFile, overlayFile);
+
+	expect(result).toEqual(expectedOutput);
+});
+
 test('fail to update a primitive string type', () => {
 	const openapiFile = "test/openapi/immutable.yaml";
 	const overlayFile = "test/overlays/immutable.yaml";

test/overlays/update-array.yaml

@@ -0,0 +1,9 @@
+overlay: 1.0.0
+info:
+  title: Structured Overlay
+  version: 1.0.0
+actions:
+- target: $.servers
+  update:
+  - url: https://example.com/prod
+    description: Production server