bug#7403: Unused variable `$source' in the depcomp script?

[Stefano Lattarini]

Hello automakers.

In the git master branch:
 $ grep '\<source\>' lib/depcomp 
   source      Source file read by `PROGRAMS ARGS'.
 if test -z "$depmode" || test -z "$source" || test -z "$object"; then
   echo "depcomp: Variables source, object and depmode must be set" 1>&2
     # the object too, otherwise makedepend will parse it as a source file.

Does this mean that the `$source' variable is really not required
by depcomp, or am I missing something?

Regards,
  Stefano