fix: should now call default schema compilers

lib/schema-controller.js

@@ -15,12 +15,16 @@ function buildSchemaController (parentSchemaCtrl, opts) {
     return new SchemaController(parentSchemaCtrl, opts)
   }
 
-  let compilersFactory = {
-    buildValidator: ValidatorSelector(),
-    buildSerializer: SerializerSelector()
+  const compilersFactory = Object.assign({
+    buildValidator: null,
+    buildSerializer: null
+  }, opts?.compilersFactory)
+
+  if (!compilersFactory.buildValidator) {
+    compilersFactory.buildValidator = ValidatorSelector()
   }
-  if (opts && opts.compilersFactory) {
-    compilersFactory = Object.assign(compilersFactory, opts.compilersFactory)
+  if (!compilersFactory.buildSerializer) {
+    compilersFactory.buildSerializer = SerializerSelector()
   }
 
   const option = {

test/schema-special-usage.test.js

@@ -702,3 +702,45 @@ test('Custom schema object should not trigger FST_ERR_SCH_DUPLICATE', async t =>
   await fastify.ready()
   t.pass('fastify is ready')
 })
+
+test('The default schema compilers should not be called when overwritte by the user', async t => {
+  const Fastify = t.mock('../', {
+    '@fastify/ajv-compiler': () => {
+      t.fail('The default validator compiler should not be called')
+    },
+    '@fastify/fast-json-stringify-compiler': () => {
+      t.fail('The default serializer compiler should not be called')
+    }
+  })
+
+  const fastify = Fastify({
+    schemaController: {
+      compilersFactory: {
+        buildValidator: function factory () {
+          t.pass('The custom validator compiler should be called')
+          return function validatorCompiler () {
+            return () => { return true }
+          }
+        },
+        buildSerializer: function factory () {
+          t.pass('The custom serializer compiler should be called')
+          return function serializerCompiler () {
+            return () => { return true }
+          }
+        }
+      }
+    }
+  })
+
+  fastify.get('/',
+    {
+      schema: {
+        query: { foo: { type: 'string' } },
+        response: {
+          200: { type: 'object' }
+        }
+      }
+    }, () => {})
+
+  await fastify.ready()
+})