We use <suggests> like so:

  <autotools id="glib">
...
    <suggests>
      <!-- these provide gnome implementations of glib
           extension points -->
      <dep package="gvfs"/>
      <dep package="glib-networking"/>
    </suggests>
  </autotools>


as if it somehow means "these things should be built after building glib".

It doesn't mean that at all, though.

'jhbuild build --build-optional-modules glib' just builds glib and its dependencies (and --build-optional-modules is the only argument listed in --help that says anything about suggests or 'soft depends').

Meanwhile, another module uses it in a way that seems to mean "this would be nice to have to enable optional features during my build":

 <autotools id="libchamplain">
...
   <suggests>
     <dep package="libsoup"/>
     <dep package="clutter-gtk"/>
   </suggests>
 </autotools>

When building that module, --build-optional-modules has no effect on the number of packages built (vs. giving no arguments), but --ignore-suggests results in the suggests packages being ignored.

I guess this probably means that glib is the example of invalid usage (and that I don't understand what --build-optional-modules is supposed to do, unless it overrides a config file saying the opposite).