`[[ <exp> ]]` seems to be broken

[Vosjedev]

I tried the following script:

if [[ -z "$var" ]]; then
    echo "-z var == true"
else
    echo "-z var == false"
fi

And it gave me an error:

In [26]: bashlex.parse("""
    ...: if [[ -z "$var" ]]; then
    ...:     echo "-z var == true"
    ...: else
    ...:     echo "-z var == false"
    ...: fi
    ...: """)
---------------------------------------------------------------------------
ParsingError                              Traceback (most recent call last)
Cell In[26], line 1
----> 1 bashlex.parse("""
      2 if [[ -z "$var" ]]; then
      3     echo "-z var == true"
      4 else
      5     echo "-z var == false"
      6 fi
      7 """)

File ~/.cache/pypoetry/virtualenvs/virtualposix-qB8zXGtl-py3.12/lib/python3.12/site-packages/bashlex/parser.py:610, in parse(s, strictmode, expansionlimit, convertpos)
    591 '''parse the input string, returning a list of nodes
    592 
    593 top level node kinds are:
   (...)
    607 command substitutions found during word expansion.
    608 '''
    609 p = _parser(s, strictmode=strictmode, expansionlimit=expansionlimit)
--> 610 parts = [p.parse()]
    612 class endfinder(ast.nodevisitor):
    613     def __init__(self):

File ~/.cache/pypoetry/virtualenvs/virtualposix-qB8zXGtl-py3.12/lib/python3.12/site-packages/bashlex/parser.py:691, in _parser.parse(self)
    686 def parse(self):
    687     # yacc.yacc returns a parser object that is not reentrant, it has
    688     # some mutable state. we make a shallow copy of it so no
    689     # state spills over to the next call to parse on it
    690     theparser = copy.copy(yaccparser)
--> 691     tree = theparser.parse(lexer=self.tok, context=self)
    693     return tree

File ~/.cache/pypoetry/virtualenvs/virtualposix-qB8zXGtl-py3.12/lib/python3.12/site-packages/bashlex/yacc.py:537, in LRParser.parse(self, input, lexer, debug, tracking, context)
    535     errtoken.lexer = lexer
    536 self.state = state
--> 537 tok = self.errorfunc(errtoken)
    538 if self.errorok:
    539     # User must have done some kind of panic
    540     # mode recovery on their own.  The
    541     # returned token is the next lookahead
    542     lookahead = tok

File ~/.cache/pypoetry/virtualenvs/virtualposix-qB8zXGtl-py3.12/lib/python3.12/site-packages/bashlex/parser.py:548, in p_error(p)
    544     raise errors.ParsingError('unexpected EOF',
    545                               p.lexer.source,
    546                               len(p.lexer.source))
    547 else:
--> 548     raise errors.ParsingError('unexpected token %r' % p.value,
    549                               p.lexer.source, p.lexpos)

ParsingError: unexpected token '-z' (position 7)

The same error appears with

[[ -z "$var" ]]

and

[[ "$var" == '' ]]

except in that last one the unexpected token is '"$var"'.

My conclusion from this is that the [[ command does not work correctly. Is this fixable?