Build as Flatpak

[jeremypw]

Attempt to flatpak Terminal Gtk4

Copies a fair amount of code from BlackBox for spawning commands on the host from within the sandbox, modified to fit in with existing Terminal code.

This is based on the Gtk4 port to minimize the diff, but is not intended to be merged before the port itself has been merged as quite substantial changes are required.

[danirabbit]

Ptyxis might be a better model. I think I trust Christian more to know the right sandbox holes needed https://gitlab.gnome.org/chergert/ptyxis

[jeremypw]

@danirabbit Thanks, I'll take a look. Either way it needs some fairly advanced programming (by my standards) to get Vte to work as if were installed on the host despite being in a sandbox. Its going to need a fair amount of copying from other projects! Not just a question of punching a few holes with the manifest unfortunately.

[jeremypw]

One advantage of BlackBox is that it is written in Vala so easier to understand and 'borrow' from :stuck_out_tongue_closed_eyes:

[jeremypw]

Something in the 7.1.2 release causes errors in flatpak-builder :disappointed: -

Running appstreamcli compose
Only accepting components: io.elementary.terminal, io.elementary.terminal.desktop
Processing directory: /home/jeremy/Elementary/terminal/.flatpak-builder/rofiles/rofiles-k3Bsjn/files
Composing metadata...
Run failed, some data was ignored.
Errors were raised during this compose run:
io.elementary.terminal
  E: icon-not-found

general
  E: filters-but-no-output
Refer to the generated issue report data for details on the individual problems.
Error: ERROR: appstreamcli compose failed: Child process exited with code 1

[jeremypw]

For some reason reverting to using @BASENAME@ for the output filename for the metainfo fixes the Flatpak build issue.