If `Ns' is specified on its own line, it should be ignored. This is

shitty groff behaviour.  Do the same, but raise a warning to this
effect.  This from a TODO noted by schwarze@.

7 files changed, 20 insertions, 7 deletions

diff --git a/TODO b/TODO
index 39c77e80..8d801250 100644
--- a/TODO
+++ b/TODO
@@ -246,10 +246,6 @@
   should be indented, see e.g. rpc(3);
   reported by jmc@ on discuss@  Fri, 29 Oct 2010 13:48:33 +0100
 
-- .Ns should only be effective when called by another macro,
-  not as a stand-alone macro at the beginning of a line;
-  see for example the awk(1) SYNOPSIS.
-
 - .Ns should work when called at the end of an input line, see
   the following code in vi(1):
     .It Xo
diff --git a/main.c b/main.c
index 7e4bbb3a..1bf8712c 100644
--- a/main.c
+++ b/main.c
@@ -146,6 +146,7 @@ static	const char * const	mandocerrs[MANDOCERR_MAX] = {
 	/* related to macros and nesting */
 	"skipping obsolete macro",
 	"skipping paragraph macro",
+	"skipping no-space macro",
 	"blocks badly nested",
 	"child violates parent syntax",
 	"nested displays are not portable",
diff --git a/mandoc.h b/mandoc.h
index 61a1f5ad..704ec745 100644
--- a/mandoc.h
+++ b/mandoc.h
@@ -68,6 +68,7 @@ enum	mandocerr {
 	/* related to macros and nesting */
 	MANDOCERR_MACROOBS, /* skipping obsolete macro */
 	MANDOCERR_IGNPAR, /* skipping paragraph macro */
+	MANDOCERR_IGNNS, /* skipping no-space macro */
 	MANDOCERR_SCOPENEST, /* blocks badly nested */
 	MANDOCERR_CHILD, /* child violates parent syntax */
 	MANDOCERR_NESTEDDISP, /* nested displays are not portable */
diff --git a/mdoc.7 b/mdoc.7
index 9e4eb56e..3adfb256 100644
--- a/mdoc.7
+++ b/mdoc.7
@@ -2203,6 +2203,8 @@ Suppress a space.
 Following invocation, text is interpreted as free-form text until a
 macro is encountered.
 .Pp
+This has no effect when invoked at the start of a macro line.
+.Pp
 Examples:
 .Dl \&.Fl o \&Ns \&Ar output
 .Pp
diff --git a/mdoc_html.c b/mdoc_html.c
index 11171c21..e07766fd 100644
--- a/mdoc_html.c
+++ b/mdoc_html.c
@@ -780,7 +780,8 @@ static int
 mdoc_ns_pre(MDOC_ARGS)
 {
 
-	h->flags |= HTML_NOSPACE;
+	if ( ! (MDOC_LINE & n->flags))
+		h->flags |= HTML_NOSPACE;
 	return(1);
 }
 
diff --git a/mdoc_term.c b/mdoc_term.c
index 942753b0..bad775e9 100644
--- a/mdoc_term.c
+++ b/mdoc_term.c
@@ -1151,7 +1151,8 @@ static int
 termp_ns_pre(DECL_ARGS)
 {
 
-	p->flags |= TERMP_NOSPACE;
+	if ( ! (MDOC_LINE & n->flags))
+		p->flags |= TERMP_NOSPACE;
 	return(1);
 }
 
diff --git a/mdoc_validate.c b/mdoc_validate.c
index c8d65144..1b6fd138 100644
--- a/mdoc_validate.c
+++ b/mdoc_validate.c
@@ -104,6 +104,7 @@ static	int	 post_eoln(POST_ARGS);
 static	int	 post_it(POST_ARGS);
 static	int	 post_lb(POST_ARGS);
 static	int	 post_nm(POST_ARGS);
+static	int	 post_ns(POST_ARGS);
 static	int	 post_os(POST_ARGS);
 static	int	 post_ignpar(POST_ARGS);
 static	int	 post_prol(POST_ARGS);
@@ -148,6 +149,7 @@ static	v_post	 posts_lb[] = { post_lb, NULL };
 static	v_post	 posts_nd[] = { berr_ge1, NULL };
 static	v_post	 posts_nm[] = { post_nm, NULL };
 static	v_post	 posts_notext[] = { ewarn_eq0, NULL };
+static	v_post	 posts_ns[] = { post_ns, NULL };
 static	v_post	 posts_os[] = { post_os, post_prol, NULL };
 static	v_post	 posts_rs[] = { post_rs, NULL };
 static	v_post	 posts_sh[] = { post_ignpar, hwarn_ge1, bwarn_ge1, post_sh, NULL };
@@ -249,7 +251,7 @@ const	struct valids mdoc_valids[MDOC_MAX] = {
 	{ NULL, NULL },				/* Fx */
 	{ NULL, NULL },				/* Ms */ 
 	{ NULL, posts_notext },			/* No */
-	{ NULL, posts_notext },			/* Ns */
+	{ NULL, posts_ns },			/* Ns */
 	{ NULL, NULL },				/* Nx */
 	{ NULL, NULL },				/* Ox */
 	{ NULL, NULL },				/* Pc */
@@ -1744,6 +1746,15 @@ post_rs(POST_ARGS)
 }
 
 static int
+post_ns(POST_ARGS)
+{
+
+	if (MDOC_LINE & mdoc->last->flags)
+		mdoc_nmsg(mdoc, mdoc->last, MANDOCERR_IGNNS);
+	return(1);
+}
+
+static int
 post_sh(POST_ARGS)
 {