[luatex] LuaTeX garbles special tokens in terminal output

[Henri Menke]

Dear devs,

LuaTeX somehow garbles special tokens when printing to the log using
\show.  For example when you define a macro with active end of lines,
I'd expect ^^M to be printed in the log.  However, LuaTeX replaces ^^M
with \r, mashing all the lines together into one.

Consider the follwing MWE:

\begingroup
\obeylines
\gdef\lines{
  Hello LuaTeX!

  Why do you garble newlines in
  terminal output?
}
\endgroup

\show\lines

\bye

------------------------------------------------

Here is the log with pdfTeX.

------------------------------------------------

$ pdftex test.tex
This is pdfTeX, Version 3.14159265-2.6-1.40.19 (TeX Live 2018)
(preloaded format=pdftex)
 restricted \write18 enabled.
entering extended mode
(./test.tex
> \lines=macro:
->^^MHello LuaTeX!^^M^^MWhy do you garble newlines in^^Mterminal output?^^M.
l.11 \show\lines

?
 )
No pages of output.
Transcript written on test.log.

------------------------------------------------

And here is the log with LuaTeX.

------------------------------------------------

$ luatex test.tex
This is LuaTeX, Version 1.09.0 (TeX Live 2019/dev)
 restricted system commands enabled.
(./test.tex
> \lines=macro:
.erminal output?e newlines in
l.11 \show\lines

?
)
warning  (pdf backend): no pages of output.
Transcript written on test.log.

------------------------------------------------

Cheers, Henri