This "bug" may not conceptually be in vala, but it's most convenient to discuss here I think.

In the gnome-ostree build system, it uses srcdir != builddir, but note here that srcdir is a git checkout, so the .[ch] files aren't pregenerated.  

Recently I tracked down a bug where caribou stopped building in gnome-ostree, and it turned out to be because it uses --vapidir=$(top_srcdir), but the problem is that automake's generated vala rules include a "cd $(srcdir)" before the build command.

From sub lang_vala_finish_target of automake 1.12.3:

  $output_rules .=
    "\$(srcdir)/${derived}_vala.stamp: @vala_sources\n".
# Since the C files generated from the vala sources depend on the
# ${derived}_vala.stamp file, we must ensure its timestamp is older than
# those of the C files generated by the valac invocation below (this is
# especially important on systems with sub-second timestamp resolution).
# Thus we need to create the stamp file *before* invoking valac, and to
# move it to its final location only after valac has been invoked.
    "\t${silent}rm -f \$\@ && echo stamp > \$\@-t\n".
    "\t${verbose}\$(am__cd) \$(srcdir) && $compile @vala_sources\n".
    "\t${silent}mv -f \$\@-t \$\@\n";

I guess all the vala rules are designed under the model that one is shipping pregenerated .[ch] in tarballs, so here the intention is that we compile the output into srcdir.  But I personally always want to build from source code.

Is there a vala change that could be made so automake didn't have to cd to srcdir?