[sr #110930] Have way for --synclines output be distinguished from "regular" output

[Karl O. Pinc]

URL:
  <https://savannah.gnu.org/support/?110930>

                 Summary: Have way for --synclines output be distinguished
from "regular" output
                   Group: GNU M4
               Submitter: kop
               Submitted: Wed 06 Sep 2023 05:42:47 AM UTC
                Category: None
                Priority: 5 - Normal
                Severity: 1 - Wish
                  Status: None
                 Privacy: Public
             Assigned to: None
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
        Operating System: None


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Follow-up Comments:


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Date: Wed 06 Sep 2023 05:42:47 AM UTC By: Karl O. Pinc <kop>
It's trivial for an m4 input file to produce output that looks
like output produced by the --synclines flag.  It would
be nice if there was a guaranteed way to distinguish the two.

The obvious approach would be to have something like a
--synclines-prefix option, that would allow --synclines
output to use it's argument instead of outputting "# lines ...".
But that's something of a kludge, the user must know ahead of
time what the input files are going to output in order to be
sure there are no "collisions".

Better might be a way to have --synclines always insert output
every-other line.  Even "# line" without anything following.
Then you'd know that lines with even line numbers were produced
by --synclines and lines that have odd line numbers come from
the m4 input files.

Anyway, design is called for.

I've never had an actual problem with this.  (On the other hand,
bug #110929 has prevented me from really using --synclines.)
It might be best to wait until the feature is actually needed.

My use of --synclines would be to produce a file containing lines
that map output lines to input files/lines, like:
  output line NNN is line YYY of file XYZ
for every line of the m4 output.  So what I _really_ want
for my wishlist is for m4 to produce such syncline-like output
_without_ the output the files processed by m4 would normally
produce.  But I can produce this trivially if I can distinguish
between the syncline produced lines and the "regular" m4 output.







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