Introduce a new mdoc(7) macro .Tg ("tag") to explicitly mark a place

as defining a term.  Please only use it when automatic tagging does
not work.  Manual page authors will not be required to add the new
macro; using it remains optional.  HTML output is still rudimentary
in this version and will be polished later.

Thanks to kn@ for reminding me that i have been considering since
BSDCan 2014 whether something like this might be useful.  Given
that possibilities of making automatic tagging better are running
out and there are still several situations where automatic tagging
cannot do the job, i think the time is now ripe.

Feedback and no objection from millert@; OK espie@ inoguchi@ kn@.

1 files changed, 39 insertions, 2 deletions

diff --git a/usr.bin/mandoc/mdoc_validate.c b/usr.bin/mandoc/mdoc_validate.c
index 243326aa3be..b7ae573a127 100644
--- a/usr.bin/mandoc/mdoc_validate.c
+++ b/usr.bin/mandoc/mdoc_validate.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: mdoc_validate.c,v 1.291 2020/01/19 16:16:33 schwarze Exp $ */
+/*	$OpenBSD: mdoc_validate.c,v 1.292 2020/01/19 17:59:01 schwarze Exp $ */
 /*
  * Copyright (c) 2008-2012 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2010-2020 Ingo Schwarze <schwarze@openbsd.org>
@@ -111,6 +111,7 @@ static	void	 post_sm(POST_ARGS);
 static	void	 post_st(POST_ARGS);
 static	void	 post_std(POST_ARGS);
 static	void	 post_sx(POST_ARGS);
+static	void	 post_tg(POST_ARGS);
 static	void	 post_useless(POST_ARGS);
 static	void	 post_xr(POST_ARGS);
 static	void	 post_xx(POST_ARGS);
@@ -236,6 +237,7 @@ static	const v_post mdoc_valids[MDOC_MAX - MDOC_Dd] = {
 	NULL,		/* %Q */
 	NULL,		/* %U */
 	NULL,		/* Ta */
+	post_tg,	/* Tg */
 };
 
 #define	RSORD_MAX 14 /* Number of `Rs' blocks. */
@@ -1075,6 +1077,41 @@ post_st(POST_ARGS)
 }
 
 static void
+post_tg(POST_ARGS)
+{
+	struct roff_node	*n, *nch;
+	size_t			len;
+
+	n = mdoc->last;
+	nch = n->child;
+	if (nch == NULL && n->next != NULL &&
+	    n->next->child->type == ROFFT_TEXT) {
+		mdoc->next = ROFF_NEXT_CHILD;
+		roff_word_alloc(mdoc, n->line, n->pos, n->next->child->string);
+		nch = mdoc->last;
+		nch->flags |= NODE_NOSRC;
+		mdoc->last = n;
+	}
+	if (nch == NULL || *nch->string == '\0') {
+		mandoc_msg(MANDOCERR_MACRO_EMPTY, n->line, n->pos, "Tg");
+		roff_node_delete(mdoc, n);
+		return;
+	}
+	len = strcspn(nch->string, " \t");
+	if (nch->string[len] != '\0')
+		mandoc_msg(MANDOCERR_TG_SPC, nch->line, nch->pos + len + 1,
+		    "Tg %s", nch->string);
+	if (nch->next != NULL) {
+		mandoc_msg(MANDOCERR_ARG_EXCESS, nch->next->line,
+		    nch->next->pos, "Tg ... %s", nch->next->string);
+		while (nch->next != NULL)
+			roff_node_delete(mdoc, nch->next);
+	}
+	if (nch->string[len] != '\0')
+		roff_node_delete(mdoc, n);
+}
+
+static void
 post_obsolete(POST_ARGS)
 {
 	struct roff_node *n;
@@ -1739,7 +1776,7 @@ post_bl(POST_ARGS)
 	while (nchild != NULL) {
 		nnext = nchild->next;
 		if (nchild->tok == MDOC_It ||
-		    (nchild->tok == MDOC_Sm &&
+		    ((nchild->tok == MDOC_Sm || nchild->tok == MDOC_Tg) &&
 		     nnext != NULL && nnext->tok == MDOC_It)) {
 			nchild = nnext;
 			continue;