warn about time machines; suggested by Thomas Klausner <wiz @ NetBSD>

4 files changed, 20 insertions, 2 deletions

diff --git a/mandoc.1 b/mandoc.1
index 8da51c61..ef280ab7 100644
--- a/mandoc.1
+++ b/mandoc.1
@@ -981,6 +981,14 @@ The date given in a
 or
 .Ic \&TH
 macro does not follow the conventional format.
+.It Sy "date in the future, using it anyway"
+.Pq mdoc , man
+The date given in a
+.Ic \&Dd
+or
+.Ic \&TH
+macro is more than a day ahead of the current system
+.Xr time 3 .
 .It Sy "missing Os macro, using \(dq\(dq"
 .Pq mdoc
 The default or current system is not shown in this case.
diff --git a/mandoc.c b/mandoc.c
index 7dfeec77..44ad938d 100644
--- a/mandoc.c
+++ b/mandoc.c
@@ -523,6 +523,7 @@ fail:
 char *
 mandoc_normdate(struct roff_man *man, char *in, int ln, int pos)
 {
+	char		*cp;
 	time_t		 t;
 
 	/* No date specified: use today's date. */
@@ -535,13 +536,20 @@ mandoc_normdate(struct roff_man *man, char *in, int ln, int pos)
 	/* Valid mdoc(7) date format. */
 
 	if (a2time(&t, "$" "Mdocdate: %b %d %Y $", in) ||
-	    a2time(&t, "%b %d, %Y", in))
-		return time2a(t);
+	    a2time(&t, "%b %d, %Y", in)) {
+		cp = time2a(t);
+		if (t > time(NULL) + 86400)
+			mandoc_msg(MANDOCERR_DATE_FUTURE, man->parse,
+			    ln, pos, cp);
+		return cp;
+	}
 
 	/* In man(7), do not warn about the legacy format. */
 
 	if (a2time(&t, "%Y-%m-%d", in) == 0)
 		mandoc_msg(MANDOCERR_DATE_BAD, man->parse, ln, pos, in);
+	else if (t > time(NULL) + 86400)
+		mandoc_msg(MANDOCERR_DATE_FUTURE, man->parse, ln, pos, in);
 	else if (man->macroset == MACROSET_MDOC)
 		mandoc_vmsg(MANDOCERR_DATE_LEGACY, man->parse,
 		    ln, pos, "Dd %s", in);
diff --git a/mandoc.h b/mandoc.h
index b31a5139..f284e743 100644
--- a/mandoc.h
+++ b/mandoc.h
@@ -76,6 +76,7 @@ enum	mandocerr {
 	MANDOCERR_MSEC_BAD, /* unknown manual section: Dt ... section */
 	MANDOCERR_DATE_MISSING, /* missing date, using today's date */
 	MANDOCERR_DATE_BAD, /* cannot parse date, using it verbatim: date */
+	MANDOCERR_DATE_FUTURE, /* date in the future, using it anyway: date */
 	MANDOCERR_OS_MISSING, /* missing Os macro, using "" */
 	MANDOCERR_PROLOG_REP, /* duplicate prologue macro: macro */
 	MANDOCERR_PROLOG_LATE, /* late prologue macro: macro */
diff --git a/read.c b/read.c
index 686d6fc6..b26e366e 100644
--- a/read.c
+++ b/read.c
@@ -118,6 +118,7 @@ static	const char * const	mandocerrs[MANDOCERR_MAX] = {
 	"unknown manual section",
 	"missing date, using today's date",
 	"cannot parse date, using it verbatim",
+	"date in the future, using it anyway",
 	"missing Os macro, using \"\"",
 	"duplicate prologue macro",
 	"late prologue macro",