To make it easier for me to review, could you show the HTML before and after?

If Im reading this correct. The id of the label, is the same as the id of the input. Hm.. Could you also show an example form.. This should really not be the case.

label_attr.id should be different from form.vars.id. Hm..

If Im reading this correct. The id of the label, is the same as the id of the input. Hm.. Could you also show an example form.. This should really not be the case.

label_attr.id should be different from form.vars.id. Hm..

Here is the currently generated HTML:

<div class="form-group">
    <label data-browse="Kiezen" for="form_asset" id="form_asset_label" placeholder="Bestand">Bestand</label>
    <div class="custom-file">
        <input aria-describedby="form_asset_help" class="file asset custom-file-input" id="form_asset" lang="nl" name="form[asset]" type="file">
        <label class="custom-file-label" data-browse="Kiezen" for="form_asset" id="form_asset_label" placeholder="Bestand"></label>
    </div>
</div>

As you can see the label id is reused in the widget block

Could you show me the Form class that you are using to render this?

The id should be form_asset and form_asset_label if I remember correctly.

I just tested this in a new Symfony 4.4 installation. I cannot reproduce the bug you are describing.

This is my form:

class HelloType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('field_name', TextType::class)
        ;
    }
}

With standard form theme:

<div>
  <label for="hello_field_name" class="required">Field name</label>
  <input type="text" id="hello_field_name" name="hello[field_name]" required="required">
</div>

With bootstrap

<div class="form-group">
  <label for="hello_field_name" class="required">Field name</label>
  <input type="text" id="hello_field_name" name="hello[field_name]" required="required" class="form-control">
</div>

Feel free to make a PR to https://github.com/Nyholm/sf-issue-40565 to replicate this bug.

@Nyholm this PR is about the rendering of the file input in the bootstrap theme, not the text input

Oops. Thank you @stof. You are correct. But I fail to reproduce it on the FileType too.

    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('field_name', FileType::class)
        ;
    }

<div class="form-group">
    <label for="hello_field_name" class="required">Field name</label>
    <div class="custom-file"><input type="file" id="hello_field_name" name="hello[field_name]" required="required" class="custom-file-input">
    <label for="hello_field_name" class="custom-file-label"></label>
    </div>
</div>

However, this form has multiple labels...

hmm, the issue seems to happen when you put an id in your label_attr (which is indeed not done by default).

Here is the bootstrap_4_horizontal_layout.html.twig:

<div class="form-group row">
  <label class="col-form-label col-sm-2 required" for="hello_field_name">Field name</label>
  <div class="col-sm-10">
    <div class="custom-file">
      <input type="file" id="hello_field_name" name="hello[field_name]" required="required" class="custom-file-input">
      <label for="hello_field_name" class="custom-file-label"></label>
    </div>
  </div>
</div>

@theus77, I suspect you have a lot of custom form types in your application and one of them is not acting properly.

@stof, you are correct again! =)

    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('field_name', FileType::class, [
                'label_attr' => ['id'=>'foo']
            ])
        ;
    }

<div class="form-group">
  <label id="foo" for="hello_field_name" class="required">Field name</label>
  <div class="custom-file">
    <input type="file" id="hello_field_name" name="hello[field_name]" required="required" class="custom-file-input">
    <label for="hello_field_name" id="foo" class="custom-file-label"></label>
  </div>
</div>

But hm... The only two fields with the same ID is the two <label>...

I'm wondering whether the custom label added for the custom-file-label should use label_attr at all.

I see that you reproduced it on your own. Sorry I was not able to follow on this before now.

I agree with @stof that extra label should not reuse label_attr at all (less code). I updated my PR in consequence.

Thank you for starting the work on this @theus77. I have finished this in #42049.