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, 15 insertions, 0 deletions

diff --git a/regress/mdoc/Eo/arg.out_utf8 b/regress/mdoc/Eo/arg.out_utf8
new file mode 100644
index 00000000..3b4a30bd
--- /dev/null
+++ b/regress/mdoc/Eo/arg.out_utf8
@@ -0,0 +1,15 @@
+EO-ARG(1)                   General Commands Manual                  EO-ARG(1)
+
+NNAAMMEE
+     EEoo--aarrgg – escapes in arguments of enclosure macros
+
+DDEESSCCRRIIPPTTIIOONN
+     «unquoted unescaped»
+
+     «quoted unescaped»
+
+     «unquoted escaped»
+
+     «quoted escaped»
+
+OpenBSD                        December 21, 2018                       OpenBSD