Update of bug #64300 (group groff):
Status: None => Need Info
Assigned to: gbranden => barx
Planned Release: None => 1.25.0
Summary: [troff] ignore and diagnose when `'sp` used when not
on a page (\n[nl]=-1) => [PATCH] [troff] ignore and diagnose when `'sp` used
when not on a page (\n[nl]=-1)
_______________________________________________________
Follow-up Comment #13:
Seeking code review and/or feedback from Dave.
Here's a commit I have in my private post-1.24 branch.
I **think** it makes sense.
Does this stuff look that way to you?
commit f1cfbc7e4947c073e46546de5d1738d24bd8645d (HEAD)
Author: G. Branden Robinson <[email protected]>
Date: Fri Jan 2 00:08:38 2026 -0600
NEED CHANGELOG src/roff/troff/div.cpp (space_request): Fix Savannah
#64300.
* src/roff/troff/div.cpp (space_request): If the `sp` request is invoked
with the no-break control character (that is, "'sp") when the drawing
position is off the page (as when the formatter starts up), ignore the
request and throw an error diagnostic. This is inconsistent with AT&T
troffs (including Heirloom Doctools) and neatroff, but precisely
consistent with all other requests that have different semantics when
invoked with the no-break control character. When invoked thus, none
of `br`, `brp`, `ce`, `cf`, `fi`, `fl`, `in`, `nf`, or `rj` move the
drawing position onto the page.
* tmac/doc-old.tmac (Sh): If the formatter claims groff compatibility,
simply emit a `br` request to start the (next) document instead of
invoking `sp` with the no-break control character.
* doc/groff.texi (Manipulating Spacing): Document that invoking `'sp`
in the top-level diversion when the vertical drawing position is
negative is an error.
* doc/groff.texi (Other Differences):
* man/groff_diff.7.man: (Other differences): Document difference between
AT&T and GNU troffs. (AT&T troff's behavior looks buggy to me...)
Fixes <https://savannah.gnu.org/bugs/?64300>. Thanks to Dave Kemper for
the discussion.
diff --git a/doc/groff.texi.in b/doc/groff.texi.in
index 6b9bd16e5..397b056f1 100644
--- a/doc/groff.texi.in
+++ b/doc/groff.texi.in
@@ -10716,6 +10716,17 @@
and the bottom if
@var{N}
is negative.
+
+@cindex invoking @code{sp} request with no-break control character while not
on a page
+@cindex no-break control character, invoking @code{sp} request with, while
not on a page
+@cindex control character, no-break, invoking @code{sp} request with, while
not on a page
+Invoking
+@code{sp}
+with the no-break control character
+while ``not on a page''
+(in the top-level diversion at a negative vertical drawing position)
+is an error.@footnote{See @ref{Page Control} and @ref{Other
+Differences}.}
@endDefreq
@DefreqList {ls, [@Var{count}]}
@@ -22473,6 +22484,30 @@
contents,
and other properties of each named argument.
+@cindex @code{sp} request, incompatibilities with @acronym{AT&T}
@code{troff}
+The
+@code{sp}
+request differs from @acronym{AT&T}
+@command{troff}:@: @c AT&T
+invoking
+@code{sp}
+with the no-break control character
+while ``not on a page''---that is,
+when writing output to the top-level diversion
+while the vertical drawing position reported by register
+@code{nl}
+is negative---provokes an error diagnostic
+and does not move the drawing position.
+@acronym{AT&T}
+@command{troff} @c AT&T
+sets the vertical drawing position
+to two basic units fewer than the specified argument
+(or one vee minus one basic unit if no argument is present).
+@c Yes, really. Try:
+@c $ printf '.tm \\n(nl\.c2 $\n$sp\n.tm \\n(nl\n'
+@c $ printf '.tm \\n(nl\.c2 $\n.nl tm -1\n$sp\n.tm \\n(nl\n'
+@c ...with DWB, Plan 9, and Heirloom Doctools troffs. --GBR
+
@cindex @code{ss} request, incompatibilities with @acronym{AT&T}
@code{troff}
AT&T
@command{troff} @c AT&T
diff --git a/man/groff_diff.7.man b/man/groff_diff.7.man
index d5b44d245..ddf03be1a 100644
--- a/man/groff_diff.7.man
+++ b/man/groff_diff.7.man
@@ -6836,6 +6836,31 @@ .SH "Other differences"
.
.
.P
+The
+.B sp
+request differs from AT&T
+.IR troff : \" AT&T
+invoking
+.B sp
+with the no-break control character
+while \[lq]not on a page\[rq]\[em]that is,
+when writing output to the top-level diversion
+while the vertical drawing position reported by register
+.B nl
+is negative\[em]provokes an error diagnostic
+and does not move the drawing position.
+AT&T
+.I troff \" AT&T
+sets the vertical drawing position
+to two basic units fewer than the specified argument
+(or one vee minus one basic unit if no argument is present).
+.\" Yes, really. Try:
+.\" $ printf '.tm \\n(nl\.c2 $\n$sp\n.tm \\n(nl\n'
+.\" $ printf '.tm \\n(nl\.c2 $\n.nl tm -1\n$sp\n.tm \\n(nl\n'
+.\" ...with DWB, Plan 9, and Heirloom Doctools troffs. --GBR
+.
+.
+.P
AT&T
.I troff \" AT&T
ignores the
diff --git a/src/roff/troff/div.cpp b/src/roff/troff/div.cpp
index a619713f3..c8d09d0c0 100644
--- a/src/roff/troff/div.cpp
+++ b/src/roff/troff/div.cpp
@@ -861,6 +861,13 @@ static void space_request() // .sp
postpone_traps();
if (was_invoked_with_regular_control_character)
curenv->do_break();
+ else if ((curdiv == topdiv)
+ && (topdiv->before_first_page_status > 0)) {
+ error("cannot vertically space with the no-break control character"
+ " when not on a page");
+ skip_line();
+ return;
+ }
vunits n;
if (!has_arg() || !read_vunits(&n, 'v'))
n = curenv->get_vertical_spacing();
diff --git a/tmac/doc-old.tmac b/tmac/doc-old.tmac
index b58c1f39b..e00495636 100644
--- a/tmac/doc-old.tmac
+++ b/tmac/doc-old.tmac
@@ -1706,7 +1706,8 @@ .de Sh
. in 0
.\}
.pL
-'sp
+.ie \n(.g .br
+.el 'sp \" erroneous in GNU troff when the page hasn't started
.ns
.ta .5i 1i 1.5i 2i 2.5i 3i 3.5i 4i 4.5i 5i 5.5i 6i 6.5i
.if !\\n(cR .ne 3
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