Allow default values when merging values into a resource (#48073)

Author: axlon

src/Illuminate/Http/Resources/ConditionallyLoadsAttributes.php

@@ -140,23 +140,31 @@ protected function merge($value)
      *
      * @param  bool  $condition
      * @param  mixed  $value
+     * @param  mixed  $default
      * @return \Illuminate\Http\Resources\MergeValue|mixed
      */
-    protected function mergeWhen($condition, $value)
+    protected function mergeWhen($condition, $value, $default = null)
     {
-        return $condition ? new MergeValue(value($value)) : new MissingValue;
+        if ($condition) {
+            return new MergeValue(value($value));
+        }
+
+        return func_num_args() === 3 ? new MergeValue(value($default)) : new MissingValue();
     }
 
     /**
      * Merge a value unless the given condition is truthy.
      *
      * @param  bool  $condition
      * @param  mixed  $value
+     * @param  mixed  $default
      * @return \Illuminate\Http\Resources\MergeValue|mixed
      */
-    protected function mergeUnless($condition, $value)
+    protected function mergeUnless($condition, $value, $default = null)
     {
-        return ! $condition ? new MergeValue(value($value)) : new MissingValue;
+        $arguments = func_num_args() === 2 ? [$value] : [$value, $default];
+
+        return $this->mergeWhen(! $condition, ...$arguments);
     }
 
     /**

tests/Integration/Http/ResourceTest.php

@@ -1598,6 +1598,29 @@ public function work()
         ], $results);
     }
 
+    public function testMergeValuesMayFallbackToDefaults()
+    {
+        $filter = new class
+        {
+            use ConditionallyLoadsAttributes;
+
+            public function work()
+            {
+                return $this->filter([
+                    $this->mergeUnless(false, ['Taylor', 'Mohamed'], ['First', 'Second']),
+                    $this->mergeWhen(false, ['Adam', 'Matt'], ['Abigail', 'Lydia']),
+                    'Jeffrey',
+                ]);
+            }
+        };
+
+        $results = $filter->work();
+
+        $this->assertEquals([
+            'Taylor', 'Mohamed', 'Abigail', 'Lydia', 'Jeffrey',
+        ], $results);
+    }
+
     public function testNestedMerges()
     {
         $filter = new class