From ccdf39d9cb63bb341dbb5c88c9090ac8e05b350c Mon Sep 17 00:00:00 2001
From: Ingo Schwarze <schwarze@openbsd.org>
Date: Fri, 3 Jun 2022 12:15:55 +0000
Subject: During identifier parsing, handle undefined escape sequences in the
 same way as groff: * \\ is always reduced to \ * \. is always reduced to . *
 other undefined escape sequences are usually reduced to the escape name, for
 example \G to G, except during the expansion of expanding escape sequences
 having the standard argument form (in particular \* and \n), in which case
 the backslash is preserved literally.

Yes, this is confusing indeed.
For example, the following have the same meaning:
* .ds \.   and   .ds .     which is not the same as   .ds \\.
* \*[\.]   and   \*[.]     which is not the same as   \*[\\.]
* .ds \G   and   .ds G     which is not the same as   .ds \\G
* \*[\G]   and   \*[\\G]   which is not the same as   \*[G]   <- sic!

To feel less dirty, have a leaning toothpick, if you are so inclined.

This patch also slightly improves the string shown by the "escaped
character not allowed in a name" error message.
---
 regress/roff/cond/string.in | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

(limited to 'regress/roff/cond/string.in')

diff --git a/regress/roff/cond/string.in b/regress/roff/cond/string.in
index 273984be..fedb4d81 100644
--- a/regress/roff/cond/string.in
+++ b/regress/roff/cond/string.in
@@ -1,5 +1,5 @@
-.\" $OpenBSD: string.in,v 1.4 2019/02/06 20:54:28 schwarze Exp $
-.TH STRING 1 "February 6, 2019"
+.\" $OpenBSD: string.in,v 1.5 2022/06/03 11:50:25 schwarze Exp $
+.TH STRING 1 "June 3, 2022"
 .SH NAME
 string \- conditional testing whether a string is defined
 .SH DESCRIPTION
@@ -40,3 +40,28 @@ identifier and tab:
 escape sequence after identifier:
 .ie d mystr\(enmystr is defined
 .el OOPS
+.PP
+backslash in name:
+.ds \\ value
+.ie d \\ \e is defined
+.el OOPS
+.rm \\
+.if d \\ still defined!?
+.PP
+dot in name:
+.ds . value
+.ie d . \&. is defined
+.el OOPS
+.ie d \. \e. is defined
+.el OOPS
+.rm .
+.if d . still defined!?
+.PP
+invalid escape in name:
+.ds G value
+.ie d G G is defined
+.el OOPS
+.ie d \G \eG is defined
+.el OOPS
+.rm \G
+.if d G still defined!?
-- 
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