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.

1 files changed, 19 insertions, 0 deletions

diff --git a/regress/mdoc/Bl/esc.in b/regress/mdoc/Bl/esc.in
new file mode 100644
index 00000000..60eb8a30
--- /dev/null
+++ b/regress/mdoc/Bl/esc.in
@@ -0,0 +1,19 @@
+.\" $OpenBSD: esc.in,v 1.1 2018/12/21 16:58:49 schwarze Exp $
+.Dd $Mdocdate$
+.Dt BL-ESC 1
+.Os
+.Sh NAME
+.Nm Bl-esc
+.Nd escape sequences in full block macro heads
+.Sh DESCRIPTION
+.ds a \(at
+.Bl -tag -width 2n
+.It \*a
+unquoted unescaped
+.It "\*a"
+quoted unescaped
+.It \\*a
+unquoted escaped
+.It "\\*a"
+quoted escaped
+.El