fix: Serialization of default values in createSerializer (#642)

* fix: Handle `clearOnDefault` in `createSerializer`

* chore: Fix types

---------

Co-authored-by: Francois Best <github@francoisbest.com>

Author: hugotiger

packages/nuqs/src/serializer.test.ts

@@ -1,5 +1,11 @@
 import { describe, expect, test } from 'vitest'
-import { parseAsBoolean, parseAsInteger, parseAsString } from './parsers'
+import {
+  parseAsArrayOf,
+  parseAsBoolean,
+  parseAsInteger,
+  parseAsJson,
+  parseAsString
+} from './parsers'
 import { createSerializer } from './serializer'
 
 const parsers = {
@@ -62,4 +68,27 @@ describe('serializer', () => {
     const result = serialize('?str=bar&int=-1', { str: 'foo', int: null })
     expect(result).toBe('?str=foo')
   })
+  test('clears value when setting the default value when `clearOnDefault` is used', () => {
+    const serialize = createSerializer({
+      int: parseAsInteger.withOptions({ clearOnDefault: true }).withDefault(0),
+      str: parseAsString.withOptions({ clearOnDefault: true }).withDefault(''),
+      bool: parseAsBoolean
+        .withOptions({ clearOnDefault: true })
+        .withDefault(false),
+      arr: parseAsArrayOf(parseAsString)
+        .withOptions({ clearOnDefault: true })
+        .withDefault([]),
+      json: parseAsJson()
+        .withOptions({ clearOnDefault: true })
+        .withDefault({ foo: 'bar' })
+    })
+    const result = serialize({
+      int: 0,
+      str: '',
+      bool: false,
+      arr: [],
+      json: { foo: 'bar' }
+    })
+    expect(result).toBe('')
+  })
 })

packages/nuqs/src/serializer.ts

@@ -10,9 +10,10 @@ type Base = string | URLSearchParams | URL
 type Values<Parsers extends Record<string, ParserBuilder<any>>> = Partial<{
   [K in keyof Parsers]?: ExtractParserType<Parsers[K]>
 }>
+type ParserWithOptionalDefault<T> = ParserBuilder<T> & { defaultValue?: T }
 
 export function createSerializer<
-  Parsers extends Record<string, ParserBuilder<any>>
+  Parsers extends Record<string, ParserWithOptionalDefault<any>>
 >(parsers: Parsers) {
   /**
    * Generate a query string for the given values.
@@ -41,7 +42,11 @@ export function createSerializer<
       if (!parser || value === undefined) {
         continue
       }
-      if (value === null) {
+      const isMatchingDefault =
+        parser.defaultValue !== undefined &&
+        (parser.eq ?? ((a, b) => a === b))(value, parser.defaultValue)
+
+      if (value === null || (parser.clearOnDefault && isMatchingDefault)) {
         search.delete(key)
       } else {
         search.set(key, parser.serialize(value))