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.

4 files changed, 31 insertions, 5 deletions

diff --git a/regress/usr.bin/mandoc/roff/esc/Makefile b/regress/usr.bin/mandoc/roff/esc/Makefile
index 111e59bc715..bd39e37883d 100644
--- a/regress/usr.bin/mandoc/roff/esc/Makefile
+++ b/regress/usr.bin/mandoc/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/usr.bin/mandoc/roff/esc/r.in b/regress/usr.bin/mandoc/roff/esc/r.in
new file mode 100644
index 00000000000..835121d9517
--- /dev/null
+++ b/regress/usr.bin/mandoc/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/usr.bin/mandoc/roff/esc/r.out_ascii b/regress/usr.bin/mandoc/roff/esc/r.out_ascii
new file mode 100644
index 00000000000..83ec9425d9c
--- /dev/null
+++ b/regress/usr.bin/mandoc/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/usr.bin/mandoc/roff/esc/r.out_lint b/regress/usr.bin/mandoc/roff/esc/r.out_lint
new file mode 100644
index 00000000000..d86f19ff4ad
--- /dev/null
+++ b/regress/usr.bin/mandoc/roff/esc/r.out_lint
@@ -0,0 +1 @@
+mandoc: r.in:11:7: UNSUPP: unsupported escape sequence: \r