do not render the same label id attribute twice

Author: xabbuh

Resources/views/Form/bootstrap_4_layout.html.twig

@@ -122,7 +122,7 @@
     <{{ element|default('div') }} class="custom-file">
         {%- set type = type|default('file') -%}
         {{- block('form_widget_simple') -}}
-        {%- set label_attr = label_attr|merge({ class: (label_attr.class|default('') ~ ' custom-file-label')|trim }) -%}
+        {%- set label_attr = label_attr|merge({ class: (label_attr.class|default('') ~ ' custom-file-label')|trim })|filter((value, key) => key != 'id') -%}
         <label for="{{ form.vars.id }}" {% with { attr: label_attr } %}{{ block('attributes') }}{% endwith %}>
             {%- if attr.placeholder is defined and attr.placeholder is not none -%}
                 {{- translation_domain is same as(false) ? attr.placeholder : attr.placeholder|trans({}, translation_domain) -}}

Tests/Extension/AbstractBootstrap4LayoutTest.php

@@ -1088,6 +1088,24 @@ public function testFile()
         );
     }
 
+    public function testFileLabelIdNotDuplicated()
+    {
+        $form = $this->factory->createNamed('name', FileType::class);
+
+        $this->assertWidgetMatchesXpath($form->createView(), ['id' => 'n/a', 'attr' => ['class' => 'my&class form-control-file'], 'label_attr' => ['id' => 'label-id']],
+'/div
+    [@class="custom-file"]
+    [
+        ./input
+            [@type="file"]
+            [@name="name"]
+        /following-sibling::label
+            [@for="name"][not(@id)]
+    ]
+'
+        );
+    }
+
     public function testFileWithPlaceholder()
     {
         $form = $this->factory->createNamed('name', FileType::class);