Bug: Cant submit form when using drag-and-drop on required attachment field

[mbarde]

What?

If a form has a required attachment field, it can not be submitted when user inputs file via drag-and-drop.

Steps to reproduce

1. Create form
2. Add attachment field
3. Mark it as required
4. Save
5. Drag-and-drop file into this attachment field
6. Try to submit form
7. Nothing happens

Tested in Firefox and Chrome.

Versions

• Volto 17.18.2
• Plone 6.0.11
• volto-form-block 3.9.2.
• collective.volto.formsupport 3.1.0

[mbarde]

Reason seems to be that the browsers form validation does not recognize the field as filled when using drag-and-drop on it.

I create a PR with a fix that basically just adds a dummy file to the relevant input element to solve this issue: #112

Would be nice if someone could confirm this issue and my fix.