Rename mandoc_getarg() to roff_getarg() and pass it the roff parser

struct as an argument such that after copy-in, it can call roff_expand()
once again, which used to be called roff_res() before this.  This
fixes a subtle low-level roff(7) parsing bug reported by Fabio
Scotoni <fabio at esse dot ch> in the 4.4BSD-Lite2 mdoc.samples(7)
manual page, because that page used an escaped escape sequence in
a macro argument.

To expand escaped escape sequences in quoted mdoc(7) arguments, too,
stop bypassing the call to roff_getarg() in mdoc_argv.c, function args()
for this case.  This does not solve the case of escaped escape sequences
in quoted .Bl -column phrases yet.

Because roff_expand() can make the string longer, roff_getarg() can no
longer operate in-place but needs to malloc(3) the returned string.
In the high-level parsers, free(3) that string after processing it.

4 files changed, 58 insertions, 2 deletions

diff --git a/regress/mdoc/Op/Makefile b/regress/mdoc/Op/Makefile
index 4a2d6fda..b2a79566 100644
--- a/regress/mdoc/Op/Makefile
+++ b/regress/mdoc/Op/Makefile
@@ -1,6 +1,6 @@
-# $OpenBSD: Makefile,v 1.3 2014/07/02 11:42:56 schwarze Exp $
+# $OpenBSD: Makefile,v 1.7 2018/12/21 16:58:49 schwarze Exp $
 
-REGRESS_TARGETS	= break broken punct
+REGRESS_TARGETS	= arg break broken punct
 LINT_TARGETS	= break broken punct
 
 SKIP_GROFF	= break
diff --git a/regress/mdoc/Op/arg.in b/regress/mdoc/Op/arg.in
new file mode 100644
index 00000000..2043b01e
--- /dev/null
+++ b/regress/mdoc/Op/arg.in
@@ -0,0 +1,20 @@
+.\" $OpenBSD: arg.in,v 1.1 2018/12/21 16:58:49 schwarze Exp $
+.Dd $Mdocdate: December 21 2018 $
+.Dt OP-ARG 1
+.Os
+.Sh NAME
+.Nm Op-arg
+.Nd escape sequences in the arguments of partial implicit macros
+.Sh DESCRIPTION
+.ds a \(at
+unquoted unescaped:
+.Op \*a
+.Pp
+quoted unescaped:
+.Op "\*a"
+.Pp
+unquoted escaped:
+.Op \\*a
+.Pp
+quoted escaped:
+.Op "\\*a"
diff --git a/regress/mdoc/Op/arg.out_ascii b/regress/mdoc/Op/arg.out_ascii
new file mode 100644
index 00000000..534917cb
--- /dev/null
+++ b/regress/mdoc/Op/arg.out_ascii
@@ -0,0 +1,15 @@
+OP-ARG(1)                   General Commands Manual                  OP-ARG(1)
+
+NNAAMMEE
+     OOpp--aarrgg - escape sequences in the arguments of partial implicit macros
+
+DDEESSCCRRIIPPTTIIOONN
+     unquoted unescaped: [@]
+
+     quoted unescaped: [@]
+
+     unquoted escaped: [@]
+
+     quoted escaped: [@]
+
+OpenBSD                        December 21, 2018                       OpenBSD
diff --git a/regress/mdoc/Op/arg.out_markdown b/regress/mdoc/Op/arg.out_markdown
new file mode 100644
index 00000000..5ad86f7d
--- /dev/null
+++ b/regress/mdoc/Op/arg.out_markdown
@@ -0,0 +1,21 @@
+OP-ARG(1) - General Commands Manual
+
+# NAME
+
+**Op-arg** - escape sequences in the arguments of partial implicit macros
+
+# DESCRIPTION
+
+unquoted unescaped:
+\[@]
+
+quoted unescaped:
+\[@]
+
+unquoted escaped:
+\[@]
+
+quoted escaped:
+\[@]
+
+OpenBSD - December 21, 2018