While attempting to add an array length annotation to the param_types struct field of GSignalQuery (bug 687541), I noticed the scanner was not producing the field description as an array:

      <field name="param_types" writable="1">
        <type name="GType" c:type="const GType*"/>
      </field>


By manually fixing this in the gir, I was able to verify access to the index of the length field with g_type_info_get_array_length works on the fields type info. So at least the g-ir-compiler is correctly pushing the information to the typelib. 

The resulting gir for the annotation in bug 687541 should look something like the following:

      <field name="param_types" writable="0">
        <array length="5" zero-terminated="0" c:type="const GType*">
          <type name="GType" c:type="GType"/>
        </array>
      </field>