Finally, for most* (see below) packages that are available in the elementary-stable COPR repository, nightly builds builds of their respective trunk / master branches are now available in the elementary-nightly COPR repository, too.

As those builds really are nightly builds (well, in fact, hourly, as long as my PC is running), do expect that they might be broken (at least some of the time).

Bugs! Bugs!

The vala compiler from the 0.34 branch (with 0.34.2 available in fedora 25 right now) currently contains a bug (see RHBZ#1398738) that results in invalid .vapi files being generated during package builds / rebuilds.

The FIXME recently added to the vala code in git explains the problem in more detail. Basically, functions returning fixed-size arrays are not handled correctly.

This bug is starting to affect packages in the fedora 25 repositories (for example, libnm-util). As a result of this, switchboard-plug-networking cannot be built at the moment due to a type mismatch (this affects stable and nightly builds).

Other packages might start to be affected by this bug as soon as more fedora packages that generate .vapi files during their builds are rebuilt with vala 0.34.x, so I am hoping for a fix to that issue soon.

EDIT: The linked commit from the vala git Repository does indeed contain the fix for the issue, as the developer has pointed out to me. Obviously, it will still take some time until it works its way into the next stable vala release and the fedora repositories, though.