Split tagging into a validation part including prioritization

in tag.{h,c} and {mdoc,man}_validate.c
and into a formatting part including command line argument checking
in term_tag.{h,c}, html.c, and {mdoc|man}_{term|html}.c.

Immediate functional benefits include:
* Improved prioritization of automatic tags for .Em and .Sy.
* Avoiding bogus automatic tags when .Em, .Fn, or .Sy are explicitly tagged.
* Explicit tagging of .Er and .Fl now works in HTML output.
* Automatic tagging of .IP and .TP now works in HTML output.
But mainly, this patch provides clean earth to build further improvements on.

Technical changes:
* Main program: Write a tag file for ASCII and UTF-8 output only.
* All formatters: There is no more need to delay writing the tags.
* mdoc(7)+man(7) formatters: No more need for elaborate syntax tree inspection.
* HTML formatter: If available, use the "string" attribute as the tag.
* HTML formatter: New function to write permalinks, to reduce code duplication.

Style cleanup in the vicinity while here:
* mdoc(7) terminal formatter: To set up bold font for children,
defer to termp_bold_pre() rather than calling term_fontpush() manually.
* mdoc(7) terminal formatter: Garbage collect some duplicate functions.
* mdoc(7) HTML formatter: Unify <code> handling, delete redundant functions.
* Where possible, use switch statements rather than if cascades.
* Get rid of some more Yoda notation.

The necessity for such changes was first discussed with kn@, but i didn't
bother him with a request to review the resulting -673/+782 line patch.

1 files changed, 103 insertions, 5 deletions

diff --git a/man_validate.c b/man_validate.c
index 374793e4..0c2ed8a4 100644
--- a/man_validate.c
+++ b/man_validate.c
@@ -1,7 +1,7 @@
-/*	$Id: man_validate.c,v 1.150 2020/01/19 16:44:50 schwarze Exp $ */
+/* $Id: man_validate.c,v 1.151 2020/03/13 15:32:28 schwarze Exp $ */
 /*
- * Copyright (c) 2008, 2009, 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2010, 2012-2020 Ingo Schwarze <schwarze@openbsd.org>
+ * Copyright (c) 2008, 2009, 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
  *
  * Permission to use, copy, modify, and distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
@@ -14,6 +14,8 @@
  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ * Validation module for man(7) syntax trees used by mandoc(1).
  */
 #include "config.h"
 
@@ -32,6 +34,7 @@
 #include "mandoc_aux.h"
 #include "mandoc.h"
 #include "roff.h"
+#include "tag.h"
 #include "man.h"
 #include "libmandoc.h"
 #include "roff_int.h"
@@ -45,6 +48,7 @@ static	void	  check_abort(CHKARGS) __attribute__((__noreturn__));
 static	void	  check_par(CHKARGS);
 static	void	  check_part(CHKARGS);
 static	void	  check_root(CHKARGS);
+static	void	  check_tag(struct roff_node *, struct roff_node *);
 static	void	  check_text(CHKARGS);
 
 static	void	  post_AT(CHKARGS);
@@ -54,6 +58,7 @@ static	void	  post_IP(CHKARGS);
 static	void	  post_OP(CHKARGS);
 static	void	  post_SH(CHKARGS);
 static	void	  post_TH(CHKARGS);
+static	void	  post_TP(CHKARGS);
 static	void	  post_UC(CHKARGS);
 static	void	  post_UR(CHKARGS);
 static	void	  post_in(CHKARGS);
@@ -62,8 +67,8 @@ static	const v_check man_valids[MAN_MAX - MAN_TH] = {
 	post_TH,    /* TH */
 	post_SH,    /* SH */
 	post_SH,    /* SS */
-	NULL,       /* TP */
-	NULL,       /* TQ */
+	post_TP,    /* TP */
+	post_TP,    /* TQ */
 	check_abort,/* LP */
 	check_par,  /* PP */
 	check_abort,/* P */
@@ -201,6 +206,66 @@ check_abort(CHKARGS)
 	abort();
 }
 
+/*
+ * Skip leading whitespace, dashes, backslashes, and font escapes,
+ * then create a tag if the first following byte is a letter.
+ * Priority is high unless whitespace is present.
+ */
+static void
+check_tag(struct roff_node *n, struct roff_node *nt)
+{
+	const char	*cp, *arg;
+	int		 prio, sz;
+
+	if (nt == NULL || nt->type != ROFFT_TEXT)
+		return;
+
+	cp = nt->string;
+	prio = TAG_STRONG;
+	for (;;) {
+		switch (*cp) {
+		case ' ':
+		case '\t':
+			prio = TAG_WEAK;
+			/* FALLTHROUGH */
+		case '-':
+			cp++;
+			break;
+		case '\\':
+			cp++;
+			switch (mandoc_escape(&cp, &arg, &sz)) {
+			case ESCAPE_FONT:
+			case ESCAPE_FONTBOLD:
+			case ESCAPE_FONTITALIC:
+			case ESCAPE_FONTBI:
+			case ESCAPE_FONTROMAN:
+			case ESCAPE_FONTCW:
+			case ESCAPE_FONTPREV:
+			case ESCAPE_IGNORE:
+				break;
+			case ESCAPE_SPECIAL:
+				if (sz != 1)
+					return;
+				switch (*arg) {
+				case '-':
+				case 'e':
+					break;
+				default:
+					return;
+				}
+				break;
+			default:
+				return;
+			}
+			break;
+		default:
+			if (isalpha((unsigned char)*cp))
+				tag_put(cp, prio, n);
+			return;
+		}
+	}
+}
+
 static void
 check_text(CHKARGS)
 {
@@ -332,12 +397,14 @@ check_par(CHKARGS)
 static void
 post_IP(CHKARGS)
 {
-
 	switch (n->type) {
 	case ROFFT_BLOCK:
 		if (n->head->child == NULL && n->body->child == NULL)
 			roff_node_delete(man, n);
 		break;
+	case ROFFT_HEAD:
+		check_tag(n, n->child);
+		break;
 	case ROFFT_BODY:
 		if (n->parent->head->child == NULL && n->child == NULL)
 			mandoc_msg(MANDOCERR_PAR_SKIP, n->line, n->pos,
@@ -348,6 +415,37 @@ post_IP(CHKARGS)
 	}
 }
 
+/*
+ * The first next-line element in the head is the tag.
+ * If that's a font macro, use its first child instead.
+ */
+static void
+post_TP(CHKARGS)
+{
+	struct roff_node *nt;
+
+	if (n->type != ROFFT_HEAD || (nt = n->child) == NULL)
+		return;
+
+	while ((nt->flags & NODE_LINE) == 0)
+		if ((nt = nt->next) == NULL)
+			return;
+
+	switch (nt->tok) {
+	case MAN_B:
+	case MAN_BI:
+	case MAN_BR:
+	case MAN_I:
+	case MAN_IB:
+	case MAN_IR:
+		nt = nt->child;
+		break;
+	default:
+		break;
+	}
+	check_tag(n, nt);
+}
+
 static void
 post_TH(CHKARGS)
 {