Rudimentary implementation of the \A escape sequence, following groff

semantics (test identifier for syntactical validity), not at all
following the completely unrelated Heirloom semantics (define
hyperlink target position).

The main motivation for providing this implementation is to get \A
into the parsing class ESCAPE_EXPAND that corresponds to groff parsing
behaviour, which is quite similar to the \B escape sequence (test
numerical expression for syntactical validity).  This is likely
to improve parsing of nested escape sequences in the future.

Validation isn't perfect yet.  In particular, this implementation
rejects \A arguments containing some escape sequences that groff
allows to slip through.  But that is unlikely to cause trouble even
in documents using \A for non-trivial purposes.  Rejecting the nested
escapes in question might even improve robustnest because the rejected
names are unlikely to really be usable for practical purposes - no
matter that groff dubiously considers them syntactically valid.

1 files changed, 6 insertions, 1 deletions

diff --git a/roff.c b/roff.c
index 0c36e08e..83701f7d 100644
--- a/roff.c
+++ b/roff.c
@@ -1,4 +1,4 @@
-/* $Id: roff.c,v 1.390 2022/05/31 18:09:57 schwarze Exp $ */
+/* $Id: roff.c,v 1.391 2022/05/31 20:23:05 schwarze Exp $ */
 /*
  * Copyright (c) 2010-2015, 2017-2022 Ingo Schwarze <schwarze@openbsd.org>
  * Copyright (c) 2008-2012, 2014 Kristaps Dzonsons <kristaps@bsd.lv>
@@ -1520,6 +1520,11 @@ roff_expand(struct roff *r, struct buf *buf, int ln, int pos, char ec)
 					*dst++ = '"';
 			}
 			continue;
+		case 'A':
+			ubuf[0] = iendarg > iarg ? '1' : '0';
+			ubuf[1] = '\0';
+			res = ubuf;
+			break;
 		case 'B':
 			npos = 0;
 			ubuf[0] = iendarg > iarg && iend > iendarg &&