FIX: NestedInputBuilder correctly builds filters for models with multiple relations of the same type

src/Schema/Services/NestedInputBuilder.php

@@ -184,6 +184,10 @@ protected function addInputTypesToSchema(
             }
             // If we've already seen this input, it can only be added to, not mutated.
             if ($inputType->getFieldByName($fieldName)) {
+                if ($inputType->exists() && $parentType && $parentField) {
+                    $this->schema->addType($inputType);
+                    $parentType->addField($parentField, $inputType->getName());
+                }
                 continue;
             }
 

tests/Fake/FakeProduct.php

@@ -22,6 +22,7 @@ class FakeProduct extends DataObject implements TestOnly
 
     private static $has_one = [
         'Parent' => FakeProductPage::class,
+        'FeaturedOn' => FakeProductPage::class,
     ];
 
     private static $has_many = [

tests/Fake/FakeProductPage.php

@@ -22,7 +22,8 @@ class FakeProductPage extends DataObject implements TestOnly
     private static $table_name = 'FakeProductPage_Test';
 
     private static $has_many = [
-        'Products' => FakeProduct::class,
+        'Products' => FakeProduct::class . '.Parent',
+        'FeaturedProducts' => FakeProduct::class . '.FeaturedOn',
     ];
 
     private static $owns = [

tests/Schema/Services/NestedInputBuilderTest.php

@@ -108,6 +108,34 @@ public function testNestedInputBuilderBuildsCyclicFilterFields()
         $this->assertEquals('MemberFilterFields', $filterFieldObj->getType());
     }
 
+    /**
+     * @throws SchemaBuilderException
+     */
+    public function testNestedInputBuilderBuildsRepeatedRelationsFilter()
+    {
+        $schema = (new TestSchemaBuilder())->boot('multiConnectionBuilder');
+        $schema
+            ->addModelbyClassName(FakeProductPage::class, function (ModelType $model) {
+                $model->addField('title');
+                $model->addField('products', ['plugins' => ['filter' => true]]);
+                $model->addField('featuredProducts', ['plugins' => ['filter' => true]]);
+            })
+            ->addModelbyClassName(FakeProduct::class, function (ModelType $model) {
+                $model->addField('title');
+                $model->addField('parent');
+                $model->addField('featuredOn');
+            });
+        $schema->createStoreableSchema();
+        $filterType = $schema->getType('FakeProductPageFilterFields');
+        $this->assertNotNull($filterType, "Type FakeProductPageFilterFields not found in schema");
+        $productsFilter = $filterType->getFieldByName('products');
+        $this->assertNotNull($productsFilter, "Field products not found on {$filterType->getName()}");
+        $this->assertEquals('FakeProductFilterFields', $productsFilter->getType());
+        $featuredFilter = $filterType->getFieldByName('featuredProducts');
+        $this->assertNotNull($featuredFilter, "Field featuredProducts not found on {$filterType->getName()}");
+        $this->assertEquals('FakeProductFilterFields', $featuredFilter->getType());
+    }
+
     private function assertSchema(array $graph, Schema $schema)
     {
         foreach ($graph as $typeName => $fields) {