Note that some of my last comment was before I saw the others, so I'm fine with script changes if that seems ok to others.

From Ronald:

"This is because the header file and input grammar have the same timestamp, and which forces the rebuild."

Note in the buildbot case the .[ch] files have much older timestamps than the generator script.  I think if they were the same it would be ok.  

I suspect this may be an issue now because the old svn approach was a full checkout for each build, whereas the hg approach is to pull to the local clone, and then just update the build tree.  So in the svn case all the files would have a good shot at the same timestamp, whereas with the hg approach the generated files get stale if the contents don't change.

I wonder if just doing a full checkout from the local clone would be closer to the old svn behavior in general with respect to timestamps and maybe a reasonable policy?

-- David