Emulate XeTeX font primitives in LuaTeX

test.tex

\ifdefined\directlua
  \input XeTeXemulate.sty
  \input luaotfload.sty
  \XeTeXemulate
\fi

\font\1="[lmroman10-italic.otf]" at 10pt\1
\font\2=cmr10 at 10pt

\edef\x{\the\XeTeXfonttype\1}“\x”
\edef\x{\the\XeTeXfonttype\2}“\x”

\edef\x{\the\XeTeXversion}“\x”
\edef\x{\XeTeXrevision}“\x”

\edef\x{\char\XeTeXfirstfontchar\1}“\x”
\edef\x{\char\XeTeXfirstfontchar\2}“\x”

\edef\x{\char\XeTeXlastfontchar\1}“\x”
\edef\x{\char\XeTeXlastfontchar\2}“\x”

\edef\x{\XeTeXglyph150}“\x”

\edef\x{\the\XeTeXcountglyphs\1}“\x”
\edef\x{\the\XeTeXcountglyphs\2}“\x”

\edef\x{\XeTeXglyphname\1 150}“\x”

\edef\x{\the\XeTeXglyphindex"acircumflexgrave"\relax}“\x”
\edef\x{\the\XeTeXglyphindex"acircumflexgrave" }“\x”

\edef\x{\the\XeTeXcharglyph"00A5}“\x”

\edef\x{\the\XeTeXglyphbounds 1 \XeTeXcharglyph`f}“\x”
\edef\x{\the\XeTeXglyphbounds 2 \XeTeXcharglyph`f}“\x”
\edef\x{\the\XeTeXglyphbounds 3 \XeTeXcharglyph`f}“\x”
\edef\x{\the\XeTeXglyphbounds 4 \XeTeXcharglyph`f}“\x”

\edef\x{[\the\XeTeXglyphindex yen ] x}“\x”
\edef\x{[\the\XeTeXglyphindex "yen" ] x}“\x”
\edef\x{[\the\XeTeXglyphindex"yen"\relax] x }“\x”
\edef\x{[\the\XeTeXglyphindex"yen"] x }“\x”
\edef\x{[\the\XeTeXglyphindex "yen" *2]}“\x”
\edef\x{[\the\XeTeXglyphindex "yen"\relax*2]}“\x”

\edef\x{[\XeTeXglyphindex"yen"] }“\meaning\x”
\edef\x{[\XeTeXglyphindex] }“\meaning\x”

\bye

XeTeXemulate.sty

\ifcsname ProvidesPackage\endcsname
  \NeedsTeXFormat{LaTeX2e}
  \ProvidesPackage{XeTeXemulate}[2018/09/03 v0.0 Emulate the XeTeX font primitives in LuaTeX]
\fi

\def\XeTeXemulate{%
  \chardef\XeTeXversion=0
  \def\XeTeXrevision{.99999}%
  % Circumvent \outer error
  \csname newcount\endcsname\XeTeXtracingfonts \XeTeXtracingfonts=0
  \csname newcount\endcsname\XeTeXuseglyphmetrics \XeTeXuseglyphmetrics=1
  %
  \let\XeTeXmathcode\Umathcode
  % 
  \protected\def\XeTeXfonttype{%
    \directlua{
      local fid = token.scan_int()
      local tfmdata = font.getfont(fid)
      local fonttype = tfmdata.format == "opentype" and 2 or 0
      tex.print([[\numexpr]] .. fonttype .. [[\relax]])
    }\fontid
  }%
  %
  \protected\def\XeTeXfirstfontchar{%
    \directlua{
      local fid = token.scan_int()
      local tfmdata = font.getfont(fid)
      local min
      for slot in pairs(tfmdata.characters) do
          min = min and (slot < min and slot or min) or slot
      end
      tex.print([[\numexpr]] .. min .. [[\relax]])
    }\fontid
  }%
  %
  \protected\def\XeTeXlastfontchar{%
    \directlua{
      local fid = token.scan_int()
      local tfmdata = font.getfont(fid)
      local max
      for slot in pairs(tfmdata.characters) do
          max = max and (slot > max and slot < 2^16 and slot or max) or slot
      end
      tex.print([[\numexpr]] .. max .. [[\relax]])
    }\fontid
  }%
  %
  \def\XeTeXglyph{%
    \directlua{
      local index = token.scan_int()
      local tfmdata = font.getfont(font.current())
      if tfmdata.format \string~= "opentype" then
          tex.error([[Cannot use \string\XeTeXglyph]] .. [[ with ]] ..
                    tfmdata.name .. [[; not a native platform font]])
      end
      for slot, char in pairs(tfmdata.characters) do
          if char.index == index then
              tex.print(utf.char(char.unicode))
              return
          end
      end
    }}%
  %
  \protected\def\XeTeXcountglyphs{%
    \directlua{
      local fid = token.scan_int()
      local tfmdata = font.getfont(fid)
      local count = 0
      if tfmdata.format == "opentype" then
          for _ in pairs(tfmdata.characters) do
              count = count + 1
          end
      end
      tex.print([[\numexpr]] .. count .. [[\relax]])
    }\fontid
  }%
  %
  \def\XeTeXglyphname{%
    \directlua{
      local fid = token.scan_int()
      local index = token.scan_int()
      local tfmdata = font.getfont(fid)
      if tfmdata.format \string~= "opentype" then
          tex.error([[Cannot use \string\XeTeXglyphname]] .. [[ with ]] ..
                    tfmdata.name .. [[; not a native platform font]])
      end
      local count = 0
      for slot, char in pairs(tfmdata.shared.rawdata.descriptions) do
          if char.index == index then
              tex.print(char.name)
              return
          end
      end
    }\fontid
  }%
  %
  \protected\def\XeTeXglyphindex{%
    \directlua{
      local k = string.gsub(token.scan_string(),'"','')
      token.scan_keyword(' ') % remove optional space
      local tfmdata = font.getfont(font.current())
      if tfmdata.format \string~= "opentype" then
          tex.error([[Cannot use \string\XeTeXglyphindex]] .. [[ with ]] ..
                    tfmdata.name .. [[; not a native platform font]])
      end
      local index = 0
      for slot, char in pairs(tfmdata.shared.rawdata.descriptions) do
          if char.name == k then
              index = char.index
              break
          end
      end
      tex.print([[\numexpr]] .. index .. [[\relax]])
    }}%
  %
  \protected\def\XeTeXcharglyph{%
    \directlua{
      local id = token.scan_int()
      local tfmdata = font.getfont(font.current())
      if tfmdata.format \string~= "opentype" then
          tex.error([[Cannot use \string\XeTeXcharglyph]] .. [[ with ]] ..
                    tfmdata.name .. [[; not a native platform font]])
      end
      local index = tfmdata.characters[id].index
      tex.print([[\numexpr]] .. index .. [[\relax]])
    }}%
  %
  \protected\def\XeTeXglyphbounds{%
    \directlua{
      local edge = token.scan_int()
      local slot = token.scan_int()
      local tfmdata = font.getfont(font.current())
      if tfmdata.format \string~= "opentype" then
          tex.error([[Cannot use \string\XeTeXglyphname]] .. [[ with ]] ..
                    tfmdata.name .. [[; not a native platform font]])
      end
      for _,char in pairs(tfmdata.shared.rawdata.descriptions) do
          if char and char.index == slot then
              local bbox = char.boundingbox
              local dimen = 0
              if edge == 1 then
                  dimen = bbox and bbox[1] / 100 * 2^16 or 0
              elseif edge == 2 then
                  dimen = tfmdata.characters[char.unicode].height
              elseif edge == 3 then
                  dimen = bbox and (char.width - bbox[3]) / 100 * 2^16 or 0
              elseif edge == 4 then
                  dimen = tfmdata.characters[char.unicode].depth
              end
              tex.print([[\dimexpr]] .. tex.round(dimen) .. [[sp\relax]])
              break
          end
      end
    }}%
}

\endinput

I'd actually rather reimplement the entire thing in pure Lua and expose the commands via token.set_lua. That makes them feel a lot more like actual primitives since they expand in a single step. That will need some expandafter magic for \fontid, but other than that should be straight-forward.

@kberry https://github.com/latex3/xxetex is in the works

Thanks!