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This regularly broke things – as can be seen from the number
of packages that were opting out of it – while providing only a
dubious and partial benefit to purity that other build systems did
not “enjoy”.
It has become associated with Darwin, but was actually introduced
in 2007 as part of 67d41efde1,
a work‐in‐progress commit for KDE 4 that introduced the CMake
setup hook. It has haunted us ever since, and will presumably become
even better at doing so now that it is a dead ghost.
Of course, it is possible and even likely that more impure paths will
leak into Darwin builds from third‐party CMake modules included
in packages. However, considering it already disregarded many of the
most common macOS system paths, it will be better overall to address
these in a targeted manner than dealing with the effects of this
brute‐force hook. In the long run, a good sandbox is going to be
the solution for reliable build reproducibility on the platform.