1415440 - resetting shared FileList of input[type=file] doesn't reflect on all inputs

Status: UNCONFIRMED

(Core :: Layout: Form Controls, defect, P3)

Description

[Kaiido]

Attachment: input_files_bug.html

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:57.0) Gecko/20100101 Firefox/57.0
Build ID: 20171102181127

Steps to reproduce:

create two input[type=file] (inp1 & inp2)
On change of inp1, set the files FileList of inp1 to be inp2 one's (inp2.files = inp1.files)
At this stage all is fine, they both share the same FileList.
Now clear this FileList using inp2.value = null.


Actual results:

only inp2 value string is reset, inp1 value string stays to what it was, even though inp1.files is now empty


Expected results:

both inputs should have their value strings reset.

Comment 1

[Kaiido]

This issue is being discussed at https://github.com/whatwg/html/issues/3269#issuecomment-350601712

Comment 2

[Kaiido]

Attachment: New issues raised by #1351193

Some update on this:

Now that Firefox do support the [DataTransfer constructor][1], it is now possible to set the input[type="file"]'s files to point to a mutable FileList.

This implies that the form control must get updated when this FileList is mutated.

Currently, the UI is updated when a prepopulated FileList is set, but not when the underlying FileList is mutated.

Also, these new features implies that an input[type=file]:not([multiple]) can actually hold multiple Files in its FileList. Not sure what this implies, nor where it should best be discussed, but felt here was a good starting point.

[1](https://bugzilla.mozilla.org/show_bug.cgi?id=1351193)