Issue a STYLE message when normalizing the date format in .Dd/.TH.

Leah Neukirchen pointed out that mdoclint(1) used to warn about a
leading zero before the day number, so we know that both NetBSD and
Void Linux want the message.  It does no harm on OpenBSD because
Mdocdate always does the right thing anyway.
jmc@ agrees that it makes sense in contexts not using Mdocdate.

5 files changed, 22 insertions, 7 deletions

diff --git a/mandoc.1 b/mandoc.1
index d71db20b..6534e43e 100644
--- a/mandoc.1
+++ b/mandoc.1
@@ -853,6 +853,16 @@ Consider using the conventional
 date format
 .Dq "Month dd, yyyy"
 instead.
+.It Sy "normalizing date format to" : No ...
+.Pq mdoc , man
+The
+.Ic \&Dd
+or
+.Ic \&TH
+macro provides an abbreviated month name or a day number with a
+leading zero.
+In the formatted output, the month name is written out in full
+and the leading zero is omitted.
 .It Sy "lower case character in document title"
 .Pq mdoc , man
 The title is still used as given in the
diff --git a/mandoc.c b/mandoc.c
index 44ad938d..fd0ad7e7 100644
--- a/mandoc.c
+++ b/mandoc.c
@@ -1,7 +1,7 @@
 /*	$Id$ */
 /*
  * Copyright (c) 2008-2011, 2014 Kristaps Dzonsons <kristaps@bsd.lv>
- * Copyright (c) 2011-2015, 2017 Ingo Schwarze <schwarze@openbsd.org>
+ * Copyright (c) 2011-2015, 2017, 2018 Ingo Schwarze <schwarze@openbsd.org>
  *
  * Permission to use, copy, modify, and distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
@@ -541,6 +541,9 @@ mandoc_normdate(struct roff_man *man, char *in, int ln, int pos)
 		if (t > time(NULL) + 86400)
 			mandoc_msg(MANDOCERR_DATE_FUTURE, man->parse,
 			    ln, pos, cp);
+		else if (*in != '$' && strcmp(in, cp) != 0)
+			mandoc_msg(MANDOCERR_DATE_NORM, man->parse,
+			    ln, pos, cp);
 		return cp;
 	}
 
diff --git a/mandoc.h b/mandoc.h
index ac402f10..c3d1d6a3 100644
--- a/mandoc.h
+++ b/mandoc.h
@@ -1,7 +1,7 @@
 /*	$Id$ */
 /*
  * Copyright (c) 2010, 2011, 2014 Kristaps Dzonsons <kristaps@bsd.lv>
- * Copyright (c) 2010-2017 Ingo Schwarze <schwarze@openbsd.org>
+ * Copyright (c) 2010-2018 Ingo Schwarze <schwarze@openbsd.org>
  *
  * Permission to use, copy, modify, and distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
@@ -56,6 +56,7 @@ enum	mandocerr {
 	MANDOCERR_STYLE, /* ===== start of style suggestions ===== */
 
 	MANDOCERR_DATE_LEGACY, /* legacy man(7) date format: Dd ... */
+	MANDOCERR_DATE_NORM, /* normalizing date format to: ... */
 	MANDOCERR_TITLE_CASE, /* lower case character in document title */
 	MANDOCERR_RCS_REP, /* duplicate RCS id: ... */
 	MANDOCERR_SEC_TYPO,  /* possible typo in section name: Sh ... */
diff --git a/mdoc.7 b/mdoc.7
index 892ba192..9009630d 100644
--- a/mdoc.7
+++ b/mdoc.7
@@ -1,7 +1,7 @@
 .\"	$Id$
 .\"
 .\" Copyright (c) 2009, 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
-.\" Copyright (c) 2010, 2011, 2013-2017 Ingo Schwarze <schwarze@openbsd.org>
+.\" Copyright (c) 2010, 2011, 2013-2018 Ingo Schwarze <schwarze@openbsd.org>
 .\"
 .\" Permission to use, copy, modify, and distribute this software for any
 .\" purpose with or without fee is hereby granted, provided that the above
@@ -1234,7 +1234,7 @@ The
 .Ar month
 is the full English month name, the
 .Ar day
-is an optionally zero-padded numeral, and the
+is an integer number, and the
 .Ar year
 is the full four-digit year.
 .Pp
@@ -1264,8 +1264,8 @@ If no date string is given, the current date is used.
 .Pp
 Examples:
 .Dl \&.Dd $\&Mdocdate$
-.Dl \&.Dd $\&Mdocdate: July 21 2007$
-.Dl \&.Dd July 21, 2007
+.Dl \&.Dd $\&Mdocdate: July 2 2018$
+.Dl \&.Dd July 2, 2018
 .Pp
 See also
 .Sx \&Dt
diff --git a/read.c b/read.c
index 8d260529..92e5370a 100644
--- a/read.c
+++ b/read.c
@@ -1,7 +1,7 @@
 /*	$Id$ */
 /*
  * Copyright (c) 2008, 2009, 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
- * Copyright (c) 2010-2017 Ingo Schwarze <schwarze@openbsd.org>
+ * Copyright (c) 2010-2018 Ingo Schwarze <schwarze@openbsd.org>
  * Copyright (c) 2010, 2012 Joerg Sonnenberger <joerg@netbsd.org>
  *
  * Permission to use, copy, modify, and distribute this software for any
@@ -94,6 +94,7 @@ static	const char * const	mandocerrs[MANDOCERR_MAX] = {
 	"generic style suggestion",
 
 	"legacy man(7) date format",
+	"normalizing date format to",
 	"lower case character in document title",
 	"duplicate RCS id",
 	"possible typo in section name",