Re-classify the roff(7) \r (reverse line feed) escape sequence

from "ignore" to "unsupported" because when an input file uses it,
mandoc(1) is likely to significantly misformat the output,
usually showing parts of the output in a different order
than the author intended.

6 files changed, 37 insertions, 11 deletions

diff --git a/regress/roff/esc/Makefile b/regress/roff/esc/Makefile
index 111e59bc..bd39e378 100644
--- a/regress/roff/esc/Makefile
+++ b/regress/roff/esc/Makefile
@@ -1,15 +1,16 @@
-# $OpenBSD: Makefile,v 1.20 2022/05/01 16:18:59 schwarze Exp $
+# $OpenBSD: Makefile,v 1.21 2022/05/20 13:06:27 schwarze Exp $
 
 REGRESS_TARGETS	 = one two multi comment
-REGRESS_TARGETS	+= B bs_man bs_mdoc c c_man E1 e f h hneg l O1 o p w z
+REGRESS_TARGETS	+= B bs_man bs_mdoc c c_man E1 e f h hneg l O1 o p r w z
 REGRESS_TARGETS	+= ignore invalid unsupp
 HTML_TARGETS	 = f
-LINT_TARGETS	 = comment B h l O1 w ignore invalid unsupp
+LINT_TARGETS	 = comment B h l O1 r w ignore invalid unsupp
 
-# mandoc defect:
+# mandoc defects:
 # - \h with a negative argument replaces output characters
 #   instead of overstriking them
+# - \r does not return to the previous output line
 
-SKIP_GROFF	 = hneg
+SKIP_GROFF	 = hneg r
 
 .include <bsd.regress.mk>
diff --git a/regress/roff/esc/r.in b/regress/roff/esc/r.in
new file mode 100644
index 00000000..835121d9
--- /dev/null
+++ b/regress/roff/esc/r.in
@@ -0,0 +1,13 @@
+.\" $OpenBSD: r.in,v 1.1 2022/05/20 13:06:27 schwarze Exp $
+.Dd $Mdocdate: May 20 2022 $
+.Dt ESC-R 1
+.Os
+.Sh NAME
+.Nm esc-r
+.Nd the roff reverse line feed escape sequence
+.Sh DESCRIPTION
+.Bd -literal
+first line
+before\rafter
+last line
+.Ed
diff --git a/regress/roff/esc/r.out_ascii b/regress/roff/esc/r.out_ascii
new file mode 100644
index 00000000..83ec9425
--- /dev/null
+++ b/regress/roff/esc/r.out_ascii
@@ -0,0 +1,11 @@
+ESC-R(1)                    General Commands Manual                   ESC-R(1)
+
+NNAAMMEE
+     eesscc--rr - the roff reverse line feed escape sequence
+
+DDEESSCCRRIIPPTTIIOONN
+     first line
+     beforeafter
+     last line
+
+OpenBSD                          May 20, 2022                          OpenBSD
diff --git a/regress/roff/esc/r.out_lint b/regress/roff/esc/r.out_lint
new file mode 100644
index 00000000..d86f19ff
--- /dev/null
+++ b/regress/roff/esc/r.out_lint
@@ -0,0 +1 @@
+mandoc: r.in:11:7: UNSUPP: unsupported escape sequence: \r
diff --git a/roff.7 b/roff.7
index 6c2e3583..6ca3029d 100644
--- a/roff.7
+++ b/roff.7
@@ -1,7 +1,7 @@
-.\"	$Id: roff.7,v 1.116 2021/09/18 12:23:06 schwarze Exp $
+.\" $Id: roff.7,v 1.117 2022/05/20 13:09:13 schwarze Exp $
 .\"
+.\" Copyright (c) 2010-2019, 2022 Ingo Schwarze <schwarze@openbsd.org>
 .\" Copyright (c) 2010, 2011, 2012 Kristaps Dzonsons <kristaps@bsd.lv>
-.\" Copyright (c) 2010-2019 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
@@ -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: September 18 2021 $
+.Dd $Mdocdate: May 20 2022 $
 .Dt ROFF 7
 .Os
 .Sh NAME
@@ -2166,8 +2166,8 @@ Break the output line at the end of the current word.
 Set number register; ignored by
 .Xr mandoc 1 .
 .It Ic \er
-Move up by one line; ignored by
-.Xr mandoc 1 .
+Reverse line feed: move up by one output line.
+Currently unsupported.
 .It Ic \eS\(aq Ns Ar number Ns Ic \(aq
 Slant output; ignored by
 .Xr mandoc 1 .
diff --git a/roff_escape.c b/roff_escape.c
index 1b5dc640..fb7b92ed 100644
--- a/roff_escape.c
+++ b/roff_escape.c
@@ -103,6 +103,7 @@ roff_escape(const char *buf, const int ln, const int aesc,
 
 	case '!':
 	case '?':
+	case 'r':
 		rval = ESCAPE_UNSUPP;
 		goto out;
 
@@ -114,7 +115,6 @@ roff_escape(const char *buf, const int ln, const int aesc,
 	case '^':
 	case 'a':
 	case 'd':
-	case 'r':
 	case 't':
 	case 'u':
 	case '{':