> On 9 Jan 2020, at 13:34, Werner LEMBERG <w...@gnu.org> wrote: > >> `configure` should warn or bail on incompatible flex versions. I >> suggest we add a version check in configure.ac to ensure that flex >> version is between 2.5.37 and 2.5.39 (given that 2.5.38 and 2.5.39 >> actually works). > > What you suggest wouldn't work as expected. There is no guarantee > that `FlexLexer.h` found during compilation is the one that is used by > a recent flex version. Unfortunately, `FlexLexer.h` doesn't contain > any version information, so it is really impossible to protect against > this situation automatically.
Akim Demaille made a patch for it, see: https://lists.gnu.org/archive/html/bug-bison/2018-09/msg00020.html
