Fully support explicit tagging of .Sh and .Ss.

This fixes the offset of two lines in terminal output
and this improves HTML output by putting the id= attribute
and <a> element into the respective <h1> or <h2> element rather
than writing an additional <mark> element.

To that end, introduce node flags NODE_ID (to make the node a link
target, for example by writing an HTML id= attribute or by calling
tag_put()) and NODE_HREF (to make the node a link source, used only
in HTML output, used only to write an <a class="permalink"> element).

In particular:
* In the validator, generalize the concept of the "next node"
such that it also works before .Sh and .Ss.
* If the first argument of .Tg is empty, don't forget to complain
if there are additional arguments, which will be ignored.
* In the terminal formatter, support writing of explicit tags
for all kinds of nodes, not just for .Tg.
* In deroff(), allow nodes to have an explicit string representation
even when they aren't text nodes.  Use this for explicitly tagged
section headers.  Suprisingly, this is sufficient to make HTML
output work, without explicit code changes in the HTML formatter.
* In syntax tree output, display NODE_ID and NODE_HREF.

1 files changed, 6 insertions, 10 deletions

diff --git a/usr.bin/mandoc/mdoc_term.c b/usr.bin/mandoc/mdoc_term.c
index dab449d9da4..54252473702 100644
--- a/usr.bin/mandoc/mdoc_term.c
+++ b/usr.bin/mandoc/mdoc_term.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: mdoc_term.c,v 1.276 2020/02/27 01:25:57 schwarze Exp $ */
+/*	$OpenBSD: mdoc_term.c,v 1.277 2020/02/27 21:38:27 schwarze Exp $ */
 /*
  * Copyright (c) 2008, 2009, 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2010, 2012-2020 Ingo Schwarze <schwarze@openbsd.org>
@@ -115,7 +115,6 @@ static	int	  termp_pp_pre(DECL_ARGS);
 static	int	  termp_ss_pre(DECL_ARGS);
 static	int	  termp_sy_pre(DECL_ARGS);
 static	int	  termp_tag_pre(DECL_ARGS);
-static	int	  termp_tg_pre(DECL_ARGS);
 static	int	  termp_under_pre(DECL_ARGS);
 static	int	  termp_vt_pre(DECL_ARGS);
 static	int	  termp_xr_pre(DECL_ARGS);
@@ -242,7 +241,7 @@ static const struct mdoc_term_act mdoc_term_acts[MDOC_MAX - MDOC_Dd] = {
 	{ NULL, termp____post }, /* %Q */
 	{ NULL, termp____post }, /* %U */
 	{ NULL, NULL }, /* Ta */
-	{ termp_tg_pre, NULL }, /* Tg */
+	{ termp_skip_pre, NULL }, /* Tg */
 };
 
 static	int	 fn_prio = TAG_STRONG;
@@ -339,6 +338,10 @@ print_mdoc_node(DECL_ARGS)
 	memset(&npair, 0, sizeof(struct termpair));
 	npair.ppair = pair;
 
+	if (n->flags & NODE_ID)
+		tag_put(n->string == NULL ? n->child->string : n->string,
+		    TAG_MANUAL, p->line);
+
 	/*
 	 * Keeps only work until the end of a line.  If a keep was
 	 * invoked in a prior line, revert it to PREKEEP.
@@ -2064,13 +2067,6 @@ termp_tag_pre(DECL_ARGS)
 }
 
 static int
-termp_tg_pre(DECL_ARGS)
-{
-	tag_put(n->child->string, TAG_MANUAL, p->line);
-	return 0;
-}
-
-static int
 termp_abort_pre(DECL_ARGS)
 {
 	abort();