YaccDecodeError
Raised from DCFG.from_yacc_file() when bison fails to parse
the input .y file. The exception message includes the file path
and, when available, the stderr output from bison (file, line,
column, and source span of the syntactic error).
If bison itself is missing from PATH, the call raises a plain
ChildProcessError instead – it is an environment problem, not
a decode failure of well-formed input.