If no tags were generated at all, unlink(2) the empty tags file as

soon as the condition can be detected and do not pass it to less(1).
This may happen for man(7) pages, for preformatted pages, and for
very simple pages like true(1).  The main benefit is that :t inside
less(1) yields the clearer diagnostic message "No tags file" rather
than the mildly confusing "No such tag in tags file": the latter
might encourage further, futile attempts to jump to other tags.

Improvement suggested by Leah Neukirchen <leah at vuxu dot org>
from The Void.

2 files changed, 14 insertions, 5 deletions

diff --git a/main.c b/main.c
index a535023b..b11f7b51 100644
--- a/main.c
+++ b/main.c
@@ -1,4 +1,4 @@
-/*	$Id: main.c,v 1.331 2019/07/15 21:41:08 schwarze Exp $ */
+/*	$Id: main.c,v 1.332 2019/07/19 20:27:25 schwarze Exp $ */
 /*
  * Copyright (c) 2008-2012 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2010-2012, 2014-2019 Ingo Schwarze <schwarze@openbsd.org>
@@ -1194,7 +1194,7 @@ spawn_pager(struct tag_files *tag_files)
 
 	use_ofn = 1;
 #if HAVE_LESS_T
-	if ((cmdlen = strlen(argv[0])) >= 4) {
+	if (*tag_files->tfn != '\0' && (cmdlen = strlen(argv[0])) >= 4) {
 		cp = argv[0] + cmdlen - 4;
 		if (strcmp(cp, "less") == 0) {
 			argv[argc++] = mandoc_strdup("-T");
diff --git a/tag.c b/tag.c
index 4ba38241..43571c7f 100644
--- a/tag.c
+++ b/tag.c
@@ -1,4 +1,4 @@
-/*	$Id: tag.c,v 1.22 2019/07/10 19:39:01 schwarze Exp $ */
+/*	$Id: tag.c,v 1.23 2019/07/19 20:27:25 schwarze Exp $ */
 /*
  * Copyright (c) 2015, 2016, 2018, 2019 Ingo Schwarze <schwarze@openbsd.org>
  *
@@ -225,6 +225,7 @@ tag_write(void)
 	struct tag_entry	*entry;
 	size_t			 i;
 	unsigned int		 slot;
+	int			 empty;
 
 	if (tag_files.tfd <= 0)
 		return;
@@ -235,12 +236,16 @@ tag_write(void)
 	}
 	if ((stream = fdopen(tag_files.tfd, "w")) == NULL)
 		mandoc_msg(MANDOCERR_FDOPEN, 0, 0, "%s", strerror(errno));
+	empty = 1;
 	entry = ohash_first(&tag_data, &slot);
 	while (entry != NULL) {
-		if (stream != NULL && entry->prio >= 0)
-			for (i = 0; i < entry->nlines; i++)
+		if (stream != NULL && entry->prio >= 0) {
+			for (i = 0; i < entry->nlines; i++) {
 				fprintf(stream, "%s %s %zu\n",
 				    entry->s, tag_files.ofn, entry->lines[i]);
+				empty = 0;
+			}
+		}
 		free(entry->lines);
 		free(entry);
 		entry = ohash_next(&tag_data, &slot);
@@ -251,6 +256,10 @@ tag_write(void)
 	else
 		close(tag_files.tfd);
 	tag_files.tfd = -1;
+	if (empty) {
+		unlink(tag_files.tfn);
+		*tag_files.tfn = '\0';
+	}
 }
 
 void