I am currently doing a an apply task to compile a bunch of IDL
files to Java source files. This always happens since there is
no sensible timestamping to stop it when it isn't necessary.
For
example, I have no idea which generated Java files belong to
which IDL source file.
The java-to-idl tool I use just generates unconditionally so there
is no help there.
What I want to do is touch a file when I start building
each IDL and use this touched file to determine whether or not
to build each IDL file.

My apply statement typically looks something like;

I don't know how many IDL files there are so I can't make one
target per file. So, what I need to happen is for the apply task
to process each file in its fileset conditionally based either
upon properties or a timestamp check that I can specify.

This doesn't appear to be possible. This surprises me a bit
as I had expected Ant to allow some degree of creativity in
timestamp checking :-). Am I missing something?

The candidates for a solution that I have found do not seem
very useful in this case. There is dependset, which only removes
target files and that isn't very helpful since jidl doesn't
care. There is
condistion/uptodate, which
set a property, but I can see no way to have this property
affect the behaviour of apply except by making each jidl
call a separate target.