bug/feature: 'if 1then print"valid syntax!"end' is valid syntax

[nobody <nobody+lua-list@...>]

(I strongly suspect this is known and I think I've seen this before
somewhere but couldn't find it in the archive... so here goes (again?):)

Lua 5.3 and 5.2 accept this (Lua 5.1/LuaJIT don't):

_=0_=1._=2local y x=3goto foo x=4while y do end x=5repeat x=6return
7until x::foo::if 8then x=9print'"valid" syntax!'end

Specifically, any char that cannot be part of the number implicitly ends
the token. (That is, the expected ones (space/symbols) *plus* [g-zG-Z_]
with the exception of (1) [xX] in initial '0x' or '0X' (but after two
digits like 00x or 00X it's a "valid" boundary again), and (2) [pP] for
hex literals where an exponent might follow.)  Compare
llex.c/read_numeral [1] for the details.

While it exists, it's a nice code golfing tool:

  u,v,w,x,y,z=1,2,3,4,5,6
  u=1v=2w=3x=4y=5z=6

  m=1n=1repeat print(m/n)m,n=m+n,m until m<0

Whether it's worth break^Wfixing is debatable... the simplest fix is
clearly "just don't write it like that!"

-- Marco

[1]: https://www.lua.org/source/5.3/llex.c.html#read_numeral