bug#33029: AM_LFLAGS --prefix option breaks build-aux/ylwrap script

[Sjoerd van Leent]

Dear Automake Maintainers,

Using Automake 1.15.1, I attempted to create a prefix other than the 
default "yy" for usage of the Fast Lexical Analyzer Generator. The FLEX 
arguments used for this, can be set using Automake option AM_LFLAGS and 
friends. Doing this with the --prefix argument however, causes a 
side-effect which the ylwrap script fails to act on. The option does not 
only replace yy inside the generated lex.yy.c file, but also changes 
lex.yy.c to become lex.<PREFIX>.c. This behavior breaks the ylwrap 
script, as it can no longer find lex.yy.c and therefore no longer move 
and rename it to the proper location (breaking the build process).

I managed my way around this, by forcing flex to generate a lex.yy.c 
file (adding -o lex.yy.c also to AM_LFLAGS). The solution to my mind is 
simple: if --prefix is used in the AM_LFLAGS and friends option, the 
ylwrap script should either expect this new prefix as a replacement 
token of the "yy" part of lex.yy.c, or ylwrap should add -o lex.yy.c on 
it's own initiative.

I hope that you are able to aid in repairing this minor deefficiency,
Best Regards,
Sjoerd van Leent