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, 21 insertions, 0 deletions

diff --git a/regress/usr.bin/mandoc/mdoc/Li/arg.out_markdown b/regress/usr.bin/mandoc/mdoc/Li/arg.out_markdown
new file mode 100644
index 00000000000..1b0ba54e809
--- /dev/null
+++ b/regress/usr.bin/mandoc/mdoc/Li/arg.out_markdown
@@ -0,0 +1,21 @@
+LI-ARG(1) - General Commands Manual
+
+# NAME
+
+**Li-arg** - escape sequences in arguments of in-line macros
+
+# DESCRIPTION
+
+unquoted unescaped:
+`@`
+
+quoted unescaped:
+`@`
+
+unquoted escaped:
+`@`
+
+quoted escaped:
+`@`
+
+OpenBSD - December 21, 2018