feat: ajv coerce array (#3594)

docs/Reference/Validation-and-Serialization.md

@@ -235,10 +235,9 @@ fastify.post('/the/url', { schema }, handler)
 the types specified in your schema `type` keywords, both to pass the validation
 and to use the correctly typed data afterwards.*
 
-The Ajv default configuration in Fastify doesn't support coercing array
-parameters in querystring. However, Fastify allows
-[`customOptions`](./Server.md#ajv) in Ajv instance. The `coerceTypes: 'array'`
-will coerce one parameter to a single element in array. Example:
+The Ajv default configuration in Fastify supports coercing array
+parameters in `querystring`.  
+Example:
 
 ```js
 const opts = {
@@ -256,37 +255,14 @@ const opts = {
 }
 
 fastify.get('/', opts, (request, reply) => {
-  reply.send({ params: request.query })
+  reply.send({ params: request.query }) // echo the querystring
 })
 
 fastify.listen(3000, (err) => {
   if (err) throw err
 })
 ```
 
-Using Fastify defaults the following request will result in `400` status code:
-
-```sh
-curl -X GET "http://localhost:3000/?ids=1
-
-{"statusCode":400,"error":"Bad Request","message":"querystring/hello should be array"}
-```
-
-Using `coerceTypes` as 'array' will fix it:
-
-```js
-const ajv = new Ajv({
-  removeAdditional: true,
-  useDefaults: true,
-  coerceTypes: 'array', // This line
-  allErrors: true
-})
-
-fastify.setValidatorCompiler(({ schema, method, url, httpPart }) => {
-  return ajv.compile(schema)
-})
-```
-
 ```sh
 curl -X GET "http://localhost:3000/?ids=1
 

package.json

@@ -176,7 +176,7 @@
     "yup": "^0.32.11"
   },
   "dependencies": {
-    "@fastify/ajv-compiler": "^2.1.0",
+    "@fastify/ajv-compiler": "^3.0.0",
     "@fastify/fast-json-stringify-compiler": "^1.0.0",
     "abstract-logging": "^2.0.1",
     "avvio": "^8.1.0",

test/schema-feature.test.js

@@ -1695,7 +1695,7 @@ test('Should throw if not default validator passed', async t => {
   }
 })
 
-test('Should throw if not default validator passed', async t => {
+test('Should coerce the array if the default validator is used', async t => {
   t.plan(2)
   const someSchema = {
     $id: 'some',
@@ -1733,7 +1733,7 @@ test('Should throw if not default validator passed', async t => {
         }
       },
       (req, reply) => {
-        reply.send({ noop: 'noop' })
+        reply.send(req.query)
       }
     )
 
@@ -1745,12 +1745,12 @@ test('Should throw if not default validator passed', async t => {
       method: 'POST',
       url: '/',
       query: {
-        msg: ['string']
+        msg: 'string'
       }
     })
 
-    t.equal(res.json().message, 'querystring/msg must be array')
-    t.equal(res.statusCode, 400, 'Should not coearce the string into array')
+    t.equal(res.statusCode, 200)
+    t.same(res.json(), { msg: ['string'] }, 'Should coearce the string into array')
   } catch (err) {
     t.error(err)
   }