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, 25 insertions, 0 deletions

diff --git a/regress/mdoc/Bl/esc.out_markdown b/regress/mdoc/Bl/esc.out_markdown
new file mode 100644
index 00000000..780a61b8
--- /dev/null
+++ b/regress/mdoc/Bl/esc.out_markdown
@@ -0,0 +1,25 @@
+BL-ESC(1) - General Commands Manual
+
+# NAME
+
+**Bl-esc** - escape sequences in full block macro heads
+
+# DESCRIPTION
+
+@
+
+> unquoted unescaped
+
+@
+
+> quoted unescaped
+
+@
+
+> unquoted escaped
+
+@
+
+> quoted escaped
+
+OpenBSD - December 21, 2018