I would like to comment on collapsed diff, at file level instead of line level

Description of the problem

From https://gitlab.com/gitlab-org/gitlab-ce/issues/20327#note_13374158

"It would be awesome if I can describe what happened in a given file, at the collapsed file level. In other words, a comment box at the file level instead of the line level. It is helpful since often a file appears in the diff that has lots of insignificant changes with which I do not wish to bore the reviewer."

Think of it as a commit message, but added at the file level in the MR instead of from the command line.

\cc @smcgivern @lukebabb @DouweM

Solution

We give file headers a floating element like the one we have for individual.

When the button is clicked, a text input for a new comment shows up.

Added comments show up at the top of the file, before the content.