Rollback declarations should be improved in several files about latex2e HOT 2 OPEN

Moving here as comments in PRs not so easy to reference later if fixed in a separate PR

Currently rolling back luatex prior to 2015 gives

! Undefined control sequence.
\@ifundefined ...e \expandafter \ifx \lastnamedcs 

as unprefixed luatex commands are undefined by the rollback.

We could do

  for _,i in pairs(tex.extraprimitives("luatex")) do
  if not string.match(i,"^U") then
        if not (string.match(i, "^luatex") or i == "lastnamedcs") then
                                                          %^^^^^^^^^^^

so that \lastnamedcs which is used within latexrelease.sty is left defined.

or we could define it under a custom name and then arrange to use that name for all engines within latexrelease (but that seems unnecessarily complicated) or we could remove the whole

  local i
  local t = { }
  for _,i in pairs(tex.extraprimitives("luatex")) do
    if not string.match(i,"^U") then
      if not string.match(i, "^luatex") then
        table.insert(t,i)
      end
    else
      if string.match(i,"^Uchar$") then
        table.insert(t,i)
      end
    end
  end
  for _,i in pairs(t) do
    tex.print(
      "\noexpand\\let\noexpand\\" .. i
        .. "\noexpand\\undefined"
    )
  end

block so leave luatex primitives with both prefixed and unprefixed names in the rollback.

I suspect this last version is most likely to lead to a successful emulation if just the format is rolled back but used in a current tex system with current packages expecting luatex names.

In particular for graphics the first change allows latexrelease to load but then the package errors as

! Undefined control sequence.
l.28       \ifnum\outputmode

If the whole block is removed so \outputmode is defined then this progresses further

The suggested graphics.sty change of using

\DeclareRelease{}{1994-06-01}{graphics-2017-06-25.sty}

Then works with the current lualatex but fails on all engines with -dev as you get

Runaway argument?
"example-image.pdf" \edef \Gin@ext {\Gin@sepdefault \filename@ext }\ifx \ETC

as kernel utf8 filename normalisation it's expecting a catcode 12 .pdf but the rolled back package is using a catcode 11.
but I haven't traced fully yet.

from latex2e.

actually I think the runaway error is just an artefact of my tests,

from latex2e.