caching behavior

[Andreas Hartmetz]

Hi,

mjansen's mail about caching in FindTaglib.cmake reminded me of something: 
FindFoo.cmake modules often like to cache the fact that something is *not* 
present. CMake also caches install locations and library versions and never 
re-checks if they are still current.
The effect is that one needs to delete the cache manually way too often. I 
think other build systems handle this better (is this actually true though?).
I'd like to ask the experts if this overzealous caching behavior can be fixed 
without every build taking ages to re-check everything. Or maybe auto*'s 
approach is a good idea: make it possible to rerun configure (in our case 
cmake), possibly with a flag to recheck everything, if in doubt. currently one 
has to delete CMakeCache.txt first and retype or copy and paste all the -D* 
options every time. auto* has ./config.status.
In my experience CMake newbies are regularly confused by the unexpected 
caching behavior and ask for help on IRC.

Cheers,
Andreas