in the base system, suggest leaving .Os blank; inspired by mdoclint

4 files changed, 15 insertions, 0 deletions

diff --git a/mandoc.1 b/mandoc.1
index 11ac4ac3..afdaabe7 100644
--- a/mandoc.1
+++ b/mandoc.1
@@ -816,6 +816,12 @@ macro does not use CVS
 keyword substitution, but using it is conventionally expected in the
 .Ox
 base system.
+.It Sy "operating system explicitly specified"
+.Pq mdoc , Ox , Nx
+The
+.Ic \&Os
+macro has an argument.
+In the base system, it is conventionally left blank.
 .It Sy "RCS id missing"
 .Pq Ox , Nx
 The manual page lacks the comment line with the RCS identifier
diff --git a/mandoc.h b/mandoc.h
index 166483b3..46a50be8 100644
--- a/mandoc.h
+++ b/mandoc.h
@@ -48,6 +48,7 @@ enum	mandocerr {
 
 	MANDOCERR_MDOCDATE, /* Mdocdate found: Dd ... */
 	MANDOCERR_MDOCDATE_MISSING, /* Mdocdate missing: Dd ... */
+	MANDOCERR_OS_ARG,  /* operating system explicitly specified: Os ... */
 	MANDOCERR_RCS_MISSING, /* RCS id missing */
 
 	MANDOCERR_STYLE, /* ===== start of style suggestions ===== */
diff --git a/mdoc_validate.c b/mdoc_validate.c
index 731b63c6..3f5387f4 100644
--- a/mdoc_validate.c
+++ b/mdoc_validate.c
@@ -2584,6 +2584,13 @@ out:
 	 * the operating system earlier.
 	 */
 
+	if (n->child != NULL)
+		mandoc_vmsg(MANDOCERR_OS_ARG, mdoc->parse,
+		    n->child->line, n->child->pos,
+		    "Os %s (%s)", n->child->string,
+		    mdoc->meta.os_e == MANDOC_OS_OPENBSD ?
+		    "OpenBSD" : "NetBSD");
+
 	while (n->tok != MDOC_Dd)
 		if ((n = n->prev) == NULL)
 			return;
diff --git a/read.c b/read.c
index 061995b9..8f66f9ce 100644
--- a/read.c
+++ b/read.c
@@ -90,6 +90,7 @@ static	const char * const	mandocerrs[MANDOCERR_MAX] = {
 
 	"Mdocdate found",
 	"Mdocdate missing",
+	"operating system explicitly specified",
 	"RCS id missing",
 
 	"generic style suggestion",