gensym vars now use X__gensymY instead of X`gensymY

[ringabout]

close #17304

[juancarlospaco]

Why not _generated_symbol instead of gensym ?. 🤔

[Araq]

Why not _generated_symbol instead of gensym ?

Because it affects the size of the generated C code and compile-times are never fast enough.

[ringabout]

It seems that https://github.com/iffy/nim-argparse is broken because it uses the internal implementation of gensym:

  if "`gensym" in node.strVal:
    return ident(node.strVal.split("`")[0])

ref https://github.com/iffy/nim-argparse/blob/4048a76b24919807b0871dd145ba93a48c2688e7/src/argparse/macrohelp.nim#L35

[ringabout]

Should I use optNimV16Emulation or define nimOldGenSym to keep backward compatibility?

[Araq]

Looking at the patch I don't like the solution anymore. We need to find a better way.

[ringabout]

something like this should work too

  let alen = rfind(a, "__")
  if alen < 0:
    alen = a.len