[bug #62265] [tbl] tables in nroff one seem to want one too many vees

[G. Branden Robinson]

URL:
  <https://savannah.gnu.org/bugs/?62265>

                 Summary: [tbl] tables in nroff one seem to want one too many
vees
                 Project: GNU troff
            Submitted by: gbranden
            Submitted on: Thu 07 Apr 2022 10:36:05 PM UTC
                Category: Preprocessor tbl
                Severity: 2 - Minor
              Item Group: Rendering/Cosmetics
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None

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Details:

I'm getting this diagnostic when formatting our groff_char(7) page for the
terminal, with continuous rendering _disabled_.


$ ./build/test-groff -z -b -ww -Tutf8 -t -man -rcR=0 ./build/man/groff_char.7
./build/man/groff_char.7:1516: warning: table row will not fit on page 14


If we inspect the page, we see that a subsection heading immediately precedes
the table, and it has a horizontal line/rule below the first row.  (In _troff_
mode, i.e. on a typesetter, that rule would be almost zero height.  But on a
terminal it demands a full vee of space.)


   Currency symbols
       Output   Input   Unicode   Notes
      
────────────────────────────────────────────────────────────────────────



groff 1.23.0.rc1.2262‐22381      7 April 2022                              
14





groff_char(7)          Miscellaneous Information Manual         
groff_char(7)


       $        $       u0024     dollar sign


I can suppress the warning, and force the table with the its adjacent
subsection heading to the next page by `ne`eding some space before the
heading.

But I have to ask for one more vee than I really need.


$ diff -u ATTIC/groff_char_*
--- ATTIC/groff_char_nowarn.7   2022-04-08 08:27:25.908132694 +1000
+++ ATTIC/groff_char_warn.7     2022-04-08 08:28:23.064206026 +1000
@@ -1507,7 +1507,7 @@
 .
 .
 .br
-.ne 5v
+.ne 4v
 .\" ====================================================================
 .SS "Currency symbols"
 .\" ====================================================================


If we ask for 5 vees, then we see that the subsection heading, column heading,
horizontal rule, and first row of data take up only 4 vees.


                \[bs]   ‐‐‐       Bell System logo +







groff 1.23.0.rc1.2262‐22381      7 April 2022                              
14





groff_char(7)          Miscellaneous Information Manual         
groff_char(7)


   Currency symbols
       Output   Input   Unicode   Notes
      
────────────────────────────────────────────────────────────────────────
       $        $       u0024     dollar sign



So what gives?




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