> I recall Facebook's own build system does list .deps files as a dependency in the makefile. When that does happen they re-exec the entire make process anew, forcing recomputation of dependencies. 

No, that doesn't happen either. When make is run, the whole set of makefiles are parsed from scratch, so there is no "recomputation of dependencies", dependencies are computed from scratch each time Make runs. There are tricks that need putting files as a dependency for the Makefile itself, but that's only necessary to change the Makefile "on the fly".

For example, if you generate the dependencies as a target and then you want Make to re-read them and re-parse the makefile. Maybe this was necessary with `--makedepend` (which doesn't create any file so there is nothing to be changed there) but it's not with `--makedepfile` because dependencies are generate while you are building the object, and that's the beauty of it :)

I agree with the resilience argument though, but for that I insist, there is no need to check if the file changed and only overwrite in that case. I will happily implement it but always rewriting, the extra logic is not needed really (at least for what I see).