grog doesn't detect files that contain .so

[Eli Zaretskii]

If you run 'grog' on a man page that contains only a .so line, it
fails to produce the correct Groff command needed to format the man
page.  E.g., try this with pdftexi2dvi.1 from the Texinfo package.
The file contains a single line:

  .so man1/texi2dvi.1

But running 'grog' on it produces this:

  groff pdftexi2dvi.1

which omits the crucial -man switch.  Running 'grog' on texi2dvi.1
does produce the correct command.  So it sounds like 'grog' doesn't
include the file mentioned on the .so line?

This is with Groff 1.22.3.  I tried the version of 'grog' and subs.pl
in the Groff Git repository, but the result was the same.

Am I doing something wrong or is this a (perhaps known) bug?

The reason I need this to work is that I have a script to format man
pages which runs 'grog' and then executes the command it produces.  I
recently noticed that it misformats some man pages, and digging into
that led me to this conclusion.

P.S. Please cc me on any responses, as I'm not subscribed to the list.

TIA