Implement the man(7) .MR macro, a 2023 GNU extension.

The syntax and semantics is almost identical to mdoc(7) .Xr.

This will be needed for reading the groff manual pages once our port
will be updated to 1.23, and the Linux Manual Pages Project is also
determined to start using it sooner or later.  I did not advocate for
this new macro, but since we want to remain able to read all manual
pages found in the wild, there is little choice but to support it.
At least it is easy to do, they basically copied .Xr.

5 files changed, 89 insertions, 2 deletions

diff --git a/regress/man/MR/Makefile b/regress/man/MR/Makefile
new file mode 100644
index 00000000..7ab2a9ee
--- /dev/null
+++ b/regress/man/MR/Makefile
@@ -0,0 +1,7 @@
+# $OpenBSD: Makefile,v 1.1 2023/10/24 20:30:49 schwarze Exp $
+
+# disable for now because groff changed the global indentation
+#REGRESS_TARGETS	 = basic
+LINT_TARGETS	 = basic
+
+.include <bsd.regress.mk>
diff --git a/regress/man/MR/basic.in b/regress/man/MR/basic.in
new file mode 100644
index 00000000..adb531a5
--- /dev/null
+++ b/regress/man/MR/basic.in
@@ -0,0 +1,46 @@
+.\" $OpenBSD: basic.in,v 1.1 2023/10/24 20:30:49 schwarze Exp $
+.TH MR-BASIC 1 "October 24, 2023" OpenBSD
+.SH NAME
+MR-basic \- manual page cross references
+.SH DESCRIPTION
+empty:
+.MR
+prints empty name and parentheses
+.PP
+single argument:
+.MR name
+prints empty parentheses
+.PP
+two arguments:
+.MR test 1
+normal use
+.PP
+three arguments:
+.MR test 1 suffix
+with suffix
+.PP
+four arguments:
+.MR test 1 suffix excess
+warning
+.PP
+five arguments:
+.MR test 1 suffix too many
+warning
+.PP
+after setting
+.ft B
+bold
+font:
+.MR test 1 suffix
+not bold
+.PP
+in bold next-line scope:
+.B
+.MR test 1 suffix
+not bold
+.TP 5n
+first tag
+first body
+.TP
+.MR test 1 tag
+test body
diff --git a/regress/man/MR/basic.out_ascii b/regress/man/MR/basic.out_ascii
new file mode 100644
index 00000000..d386ba0b
--- /dev/null
+++ b/regress/man/MR/basic.out_ascii
@@ -0,0 +1,29 @@
+MR-BASIC(1)                 General Commands Manual                MR-BASIC(1)
+
+NNAAMMEE
+     MR-basic - manual page cross references
+
+DDEESSCCRRIIPPTTIIOONN
+     empty: () prints empty name and parentheses
+
+     single argument: name() prints empty parentheses
+
+     two arguments: test(1) normal use
+
+     three arguments: test(1)suffix with suffix
+
+     four arguments: test(1)suffix warning
+
+     five arguments: test(1)suffix warning
+
+     after setting bboolldd ffoonntt:: test(1)suffix not bold
+
+     in bold next-line scope: test(1)suffix not bold
+
+     first tag
+          first body
+
+     test(1)tag
+          test body
+
+OpenBSD                        October 24, 2023                    MR-BASIC(1)
diff --git a/regress/man/MR/basic.out_lint b/regress/man/MR/basic.out_lint
new file mode 100644
index 00000000..d4803bcb
--- /dev/null
+++ b/regress/man/MR/basic.out_lint
@@ -0,0 +1,5 @@
+mandoc: basic.in:38:2: WARNING: line scope broken: MR breaks B
+mandoc: basic.in:7:2: ERROR: missing manual name, using "": MR
+mandoc: basic.in:11:2: WARNING: missing section argument: MR name
+mandoc: basic.in:23:19: ERROR: skipping excess arguments: MR ... excess
+mandoc: basic.in:27:19: ERROR: skipping excess arguments: MR ... too
diff --git a/regress/man/Makefile b/regress/man/Makefile
index 17a939b2..306411dc 100644
--- a/regress/man/Makefile
+++ b/regress/man/Makefile
@@ -1,6 +1,6 @@
-# $OpenBSD: Makefile,v 1.20 2022/04/27 17:04:15 schwarze Exp $
+# $OpenBSD: Makefile,v 1.21 2023/10/24 20:30:49 schwarze Exp $
 
-SUBDIR = AT B BI DT EX HP IP MT OP PD PP RS SH SS SY TH TP TS UC UR nf blank
+SUBDIR = AT B BI DT EX HP IP MR MT OP PD PP RS SH SS SY TH TP TS UC UR nf blank
 
 .include "../Makefile.sub"
 .include <bsd.subdir.mk>