From a24ea326675cbb23594f1f8885e969d7785442f9 Mon Sep 17 00:00:00 2001
From: schwarze <schwarze@openbsd.org>
Date: Sun, 19 Aug 2018 17:43:39 +0000
Subject: [PATCH] Mostly complete implementation of the 'c' (character
 available) roff conditional, except that the .char request still isn't
 supported and that behaviour differs from groff in many edge cases. But at
 least valid character names and numbers are now distinguished from invalid
 ones. This also fixes the bug that parsing of the 'c' conditional was
 incomplete, which resulted in leaking the tested character to the input
 parser at the beginning of the body when the condition was inverted.

---
 share/man/man7/roff.7 | 25 ++++++++++++++++------
 usr.bin/mandoc/roff.c | 49 ++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 63 insertions(+), 11 deletions(-)

diff --git a/share/man/man7/roff.7 b/share/man/man7/roff.7
index b2edb41e8f7..219657587b8 100644
--- a/share/man/man7/roff.7
+++ b/share/man/man7/roff.7
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: roff.7,v 1.80 2018/08/18 21:36:53 schwarze Exp $
+.\"	$OpenBSD: roff.7,v 1.81 2018/08/19 17:43:39 schwarze Exp $
 .\"
 .\" Copyright (c) 2010, 2011, 2012 Kristaps Dzonsons <kristaps@bsd.lv>
 .\" Copyright (c) 2010-2018 Ingo Schwarze <schwarze@openbsd.org>
@@ -15,7 +15,7 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: August 18 2018 $
+.Dd $Mdocdate: August 19 2018 $
 .Dt ROFF 7
 .Os
 .Sh NAME
@@ -1003,13 +1003,13 @@ is
 or
 .Sq o
 .Pq odd page ,
-it evaluates to true.
+it evaluates to true, and the
+.Ar body
+starts with the next character.
 .It
 If the first character of
 .Ar condition
 is
-.Sq c
-.Pq character available ,
 .Sq e
 .Pq even page ,
 .Sq t
@@ -1017,7 +1017,20 @@ is
 or
 .Sq v
 .Pq vroff mode ,
-it evaluates to false.
+it evaluates to false, and the
+.Ar body
+starts with the next character.
+.It
+If the first character of
+.Ar condition
+is
+.Sq c
+.Pq character available ,
+it evaluates to true if the following character is an ASCII character
+or a valid character escape sequence, or to false otherwise.
+The
+.Ar body
+starts with the character following that next character.
 .It
 If the first character of
 .Ar condition
diff --git a/usr.bin/mandoc/roff.c b/usr.bin/mandoc/roff.c
index b889e9f4a91..c085475e901 100644
--- a/usr.bin/mandoc/roff.c
+++ b/usr.bin/mandoc/roff.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: roff.c,v 1.207 2018/08/18 22:04:32 schwarze Exp $ */
+/*	$OpenBSD: roff.c,v 1.208 2018/08/19 17:43:39 schwarze Exp $ */
 /*
  * Copyright (c) 2008-2012, 2014 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2010-2015, 2017, 2018 Ingo Schwarze <schwarze@openbsd.org>
@@ -2166,9 +2166,10 @@ out:
 static int
 roff_evalcond(struct roff *r, int ln, char *v, int *pos)
 {
-	char	*cp, *name;
-	size_t	 sz;
-	int	 deftype, number, savepos, istrue, wanttrue;
+	const char	*start, *end;
+	char		*cp, *name;
+	size_t		 sz;
+	int		 deftype, len, number, savepos, istrue, wanttrue;
 
 	if ('!' == v[*pos]) {
 		wanttrue = 0;
@@ -2183,12 +2184,50 @@ roff_evalcond(struct roff *r, int ln, char *v, int *pos)
 	case 'o':
 		(*pos)++;
 		return wanttrue;
-	case 'c':
 	case 'e':
 	case 't':
 	case 'v':
 		(*pos)++;
 		return !wanttrue;
+	case 'c':
+		do {
+			(*pos)++;
+		} while (v[*pos] == ' ');
+
+		/*
+		 * Quirk for groff compatibility:
+		 * The horizontal tab is neither available nor unavailable.
+		 */
+
+		if (v[*pos] == '\t') {
+			(*pos)++;
+			return 0;
+		}
+
+		/* Printable ASCII characters are available. */
+
+		if (v[*pos] != '\\') {
+			(*pos)++;
+			return wanttrue;
+		}
+
+		end = v + ++*pos;
+		switch (mandoc_escape(&end, &start, &len)) {
+		case ESCAPE_SPECIAL:
+			istrue = mchars_spec2cp(start, len) != -1;
+			break;
+		case ESCAPE_UNICODE:
+			istrue = 1;
+			break;
+		case ESCAPE_NUMBERED:
+			istrue = mchars_num2char(start, len) != -1;
+			break;
+		default:
+			istrue = !wanttrue;
+			break;
+		}
+		*pos = end - v;
+		return istrue == wanttrue;
 	case 'd':
 	case 'r':
 		cp = v + *pos + 1;
-- 
2.20.1