[bug #65983] [troff] starts document preumaturely upon `lf` request

[G. Branden Robinson]

URL:
  <https://savannah.gnu.org/bugs/?65983>

                 Summary: [troff] starts document preumaturely upon `lf`
request
                   Group: GNU roff
               Submitter: gbranden
               Submitted: Sat 13 Jul 2024 07:36:37 AM UTC
                Category: Core
                Severity: 3 - Normal
              Item Group: Warning/Suspicious behaviour
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None


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Follow-up Comments:


-------------------------------------------------------
Date: Sat 13 Jul 2024 07:36:37 AM UTC By: G. Branden Robinson <gbranden>
...angering output drivers.

Spawned off of bug #65980.

Use of preprocessors with empty inputs causes the formatter to produce output
that provokes complaints from output drivers.

Example:


$ echo . | tbl
.if !\n(.g .ab GNU tbl requires groff extensions; aborting
.do if !dTS .ds TS
.do if !dT& .ds T&
.do if !dTE .ds TE
.lf 1 -
.
$ echo . | tbl | nroff
grotty:<standard input>:(<standard input>):6: fatal error: 'V' command invalid
before first 'p' command


So what's the problem?


$ echo . | tbl | nroff -Z
x T utf8
x res 240 24 40
x init
x F -
x trailer
V2640
x stop


Experimentation reveals that


.lf 1 -


...is the culprit.


$ echo ".lf 1 -" | nroff
grotty:<standard input>:(<standard input>):6: fatal error: 'V' command invalid
before first 'p' command









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