[Scons-users] Another question about a strange tool

[Tom Tanner (BLOOMBERG/ LONDON)]

One of our tools has a very strange build avoidance system (which sadly can't be turned off).

It checks the timestamp of the file you feed it and if it is different to the timestamp of the target file, it rebuilds the target file and applies the timestamp of the source file.

As it runs on executables and shared libraries, it also recurses down all the shared libraries referenced.

I think this is causing moderately strange behaviour in our builds occasionally - if a library is rebuilt but doesn't change (apart from the timestamp), then the tool is not run on it. However, if some other library or executable that depends on that library is rebuilt and does change, then the tool is run, and it detects the first library has changed, and then runs itself on that library.

Given that peculiar behaviour, what I think I need to do is to make the target also depend on the timestamp of the source. I'm worried about the best way of doing this though.

I can't find out the timestamp of the source library until it is built. So 
1) Can I depend on the source files existing, in which case I can make a Value object (we're using md5sums exclusively)
2) If not
   a) Can I add a dependency in the generator (i.e. ditto)
   b) Should I add an action whose text depends on the timestamp of the source file, using something like 'echo ${ function that returns source timestamp }'

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