[bug #46914] .ce sometimes ignores right margin

[Dave]

Follow-up Comment #6, bug #46914 (project groff):

[comment #5 comment #5:]
> When filling is enabled and `ce` is used, not only does
> automatic breaking still take place in spite of no filling
> proper taking place, but adjustment does too!

Good catch!  Had I been more eagle-eyed, I would have noticed that in the
final centered block in the output posted in comment #1.

But it's clearly not _always_ happening, or the first block would be output
as:

Text can be centered with `.ce' (option-
ally              with             `.nf'
to suppress automatic  breaks)  or  with
`.ad                                 c'.


It looks like it happens only on input lines that are also being broken, and
thence on output lines that appear before the break--which is not _as_
unreasonable, as such lines are usually at or near full measure anyway.

But the "usually" is an important caveat, because it's easy to contrive a
counterexample:

$ cat ce3.roff
.ll 36n
.nh
.ce
I often say "supercalifragilisticexpialidocious" despite its atrocious sound.
.pl \n(nlu
$ nroff ce3.roff
I              often             say
"supercalifragilisticexpialidocious"
    despite its atrocious sound.

But even in the much milder case you first spotted, I agree the adjustment
serves no useful purpose: centering is _already_ a form of adjustment, and
that should take precedence since it's the form the user explicitly
requested.

Still... case 3 in comment #1 case is an interesting illustration of the
occasional usefulness of the interword adjustment in a centered line, at least
on a terminal, where spaces are a fixed width.  (This will never be true in
typesetting, where spaces can be as thin as need be.)  In a centered line
where only one space need be added, the options are the beginning, the middle,
and the end, and this is the one case where the middle actually looks best;
neither other option would make the line "look" as centered.

But I'm skeptical that's something that can be determined algorithmically in a
reliable way.  In most cases, I think turning off adjustment on centered lines
will give the best results, so that might be the best approach to take across
the board.


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