explaining "wks.in" files in wic docs

["Robert P. J. Day" <rpjday@crashcourse.ca>]

  a related number of issues related to explaining the existence of --
and rationale for -- "wks.in" files. at the moment, i see nothing in
this section:

http://docs.yoctoproject.org/dev-manual/common-tasks.html#creating-partitioned-images-using-wic

that covers the possibility of "wks.in" files (unless i totally missed
it).

  down in section 3.16.5:

http://docs.yoctoproject.org/dev-manual/common-tasks.html#using-an-existing-kickstart-file

one reads how to list all the available images with "wic list images",
and one of those listed (canned) images is "genericx86", and a bit
further down, you read:

"Here are the actual partition language commands used in the
genericx86.wks file to generate an image"

  except there is no file "genericx86.wks", it's "genericx86.wks.in"
which caused me a few minutes of confusion as i tried to "find" it.

  as i understand it, the only additional feature with "wks.in" files
is that they would contain variables that need pre-processing. and if
that's true, where in the wic processing could someone specify that a
"wks.in" file is to be used?

  i'm looking at the wic script (line 172) and i see:

    if not wks_file.endswith(".wks"):
        wks_file = engine.find_canned_image(scripts_path, wks_file)
        if not wks_file:
            raise WicError("No image named %s found, exiting.  (Use 'wic list images' "
                           "to list available images, or specify a fully-qualified OE "
                           "kickstart (.wks) filename)" % options.wks_fi

but that seems to recognize only the ".wks" suffix. where is the
support for an explicit "wks.in" file?

rday