Missing token "]" bug

[Hans Aberg]

In Bison 1.75 (and I can't try a later version), if I use
  %token left_bracket_key "["
  %token right_bracket_key "]"
that works just fine. But if I change that to
  %token left_bracket_key "["
  %token right_bracket_key "foo"
so that "]" is missing, then I get the error message:
  Error   : Bison Compiler-Compiler
  NONE:0: m4: ERROR: EOF in string

If you can reproduce this error, then there is something wrong with the way
Bison encapsulates strings before handing them over to M4.

I arrived at the problem by using an additional token
  %token substitution_begin_key "~["
but still want to to use a closing "]". Then I land on the problem above as
not every "...[..." in the token declaration has a matching "...]...".

  Hans Aberg