Partial support for the \n[an-margin] number register.

Manuals autogenerated from reStructuredText are reckless enough
to peek at this non-portable, implementation-dependent, highly
groff-specific internal register - for no good reason, because the
man(7) language natively provides in a much simpler way what they
are trying to emulate here with much fragility.

A full implementation would be very hard because it would require
access to output-device-specific formatting data at the roff(7)
preprocessor stage, which mandoc doesn't support at all.
So hardcode a few magic numbers as reStructuredText expects them
for terminal output.  For other output modes (like HTML), code using
this register is utterly broken anyway.

4 files changed, 56 insertions, 2 deletions

diff --git a/man_macro.c b/man_macro.c
index 7b4f8de8..4f00ff0a 100644
--- a/man_macro.c
+++ b/man_macro.c
@@ -235,6 +235,10 @@ blk_close(MACRO_PROT_ARGS)
 		ntok = man->last->tok;
 		man_unscope(man, nn);
 
+		if (tok == MAN_RE && nn->head->aux > 0)
+			roff_setreg(man->roff, "an-margin",
+			    nn->head->aux, '-');
+
 		/* Move a trailing paragraph behind the block. */
 
 		if (ntok == MAN_LP || ntok == MAN_PP || ntok == MAN_P) {
@@ -256,8 +260,17 @@ blk_exp(MACRO_PROT_ARGS)
 	head = roff_head_alloc(man, line, ppos, tok);
 
 	la = *pos;
-	if (man_args(man, line, pos, buf, &p))
+	if (man_args(man, line, pos, buf, &p)) {
 		roff_word_alloc(man, line, la, p);
+		if (tok == MAN_RS) {
+			if (roff_getreg(man->roff, "an-margin") == 0)
+				roff_setreg(man->roff, "an-margin",
+				    7 * 24, '=');
+			if ((head->aux = strtod(p, NULL) * 24.0) > 0)
+				roff_setreg(man->roff, "an-margin",
+				    head->aux, '+');
+		}
+	}
 
 	if (buf[*pos] != '\0')
 		mandoc_vmsg(MANDOCERR_ARG_EXCESS, man->parse, line,
diff --git a/regress/man/RS/Makefile b/regress/man/RS/Makefile
index 4c62bb30..fda516e0 100644
--- a/regress/man/RS/Makefile
+++ b/regress/man/RS/Makefile
@@ -1,6 +1,6 @@
 # $OpenBSD: Makefile,v 1.11 2015/04/06 13:34:54 schwarze Exp $
 
-REGRESS_TARGETS	 = breaking broken empty literal lonelyRE
+REGRESS_TARGETS	 = an-margin breaking broken empty literal lonelyRE
 REGRESS_TARGETS	+= nested noRE nowidth REarg width
 LINT_TARGETS	 = empty lonelyRE noRE REarg
 
diff --git a/regress/man/RS/an-margin.in b/regress/man/RS/an-margin.in
new file mode 100644
index 00000000..b14b2cae
--- /dev/null
+++ b/regress/man/RS/an-margin.in
@@ -0,0 +1,24 @@
+.TH RS-AN-MARGIN 1 "June 13, 2017" OpenBSD
+.SH NAME
+RS-an-margin \- reStructuredText peeks at an internal register
+.SH DESCRIPTION
+regular
+text
+.RS 0.0
+zero
+indent
+\n[an-margin]
+.RS 3.5
+non-zero
+indent
+\n[an-margin]
+.RE
+back to
+zero
+indent
+\n[an-margin]
+.RE
+back to
+regular
+text
+\n[an-margin]
diff --git a/regress/man/RS/an-margin.out_ascii b/regress/man/RS/an-margin.out_ascii
new file mode 100644
index 00000000..be41d4ec
--- /dev/null
+++ b/regress/man/RS/an-margin.out_ascii
@@ -0,0 +1,17 @@
+RS-AN-MARGIN(1)             General Commands Manual            RS-AN-MARGIN(1)
+
+
+
+NNAAMMEE
+       RS-an-margin - reStructuredText peeks at an internal register
+
+DDEESSCCRRIIPPTTIIOONN
+       regular text
+       zero indent 168
+          non-zero indent 252
+       back to zero indent 168
+       back to regular text 168
+
+
+
+OpenBSD                          June 13, 2017                 RS-AN-MARGIN(1)