./configure and flex, or not

[Chris Green]

While playing at building vile in Termux on my Android phone I seem to
have hit a [minor] problem with flex and its versions.

I'm running:-

    ./configure --build=aarch64-unknown-linux-gnu --prefix=/home/.cfg/bison 
--with-builtin-filters


So, firstly I get these warnings:-

    ...
    ...
    configure: WARNING: You need flex to compile builtin filters
    checking for library path... $(libdir)/vile
    checking for startup path... $(datadir)
    checking if lex supports %pointer... no
    configure: WARNING: Your lex program does not support POSIX %pointer.  Get 
flex.
    checking if lex supports character classes... no
    configure: WARNING: Your lex program does not support POSIX character 
classes.  Get flex.
    checking if lex supports options... no
    configure: WARNING: Your lex program does not support POSIX options.  Get 
flex.
    checking if lex supports states... lex conftest.l 1>&5
    configure: WARNING: disabling build for lex-filters
    ...
    ...
    Computing location to install filter programs: $(libdir)/vile
    configure: WARNING: You should get a working version of flex, for instance:
        http://invisible-island.net/reflex


If I install flex on the system it gives me version 2.6.4 which ./configure 
says:-

    ...
    ...
    checking if any filters are built-in/loadable... yes
    checking if flex is really flex... yes
    checking version of flex... 2.6.4
    configure: WARNING: Sorry - your version of flex is too unstable: 2.6.4
    checking for library path... $(libdir)/vile
    ...
    ...
    checking for spell... no
    Computing location to install filter programs: $(libdir)/vile
    configure: WARNING: You should get a working version of flex, for instance:
            http://invisible-island.net/reflex

    checking if filesystem supports mixed-case filenames... yes
    ...
    ...

I found a long thread about this (flex versions) back in 2016 but it doesn't 
really help
much in actually sorting this out.  There isn't a 'flex-old' package available 
for Termux
and, anyway, surely flex version 2.6.4 should be acceptable as it seems to be 
the standard
one I find on all my systems (xubuntu 21.04, ubuntu 20.04, current Raspbian).

I guess I could get http://invisible-island.net/reflex, will this provide an 
acceptable flex?



-- 
Chris Green