Hadrian: Symlink Breaks Cached Builds

Recreation

$ ./hadrian/build.sh --share=_cache -j --flavour=quickest
...
Error when running Shake build system:
  at action, called at src/Rules.hs:68:19 in main:Rules
  at need, called at src/Rules.hs:90:5 in main:Rules
* Depends on: _build/stage1/lib/package.conf.d/rts-1.0.conf
  at need, called at src/Rules/Register.hs:101:5 in main:Rules.Register
* Depends on: _build/stage1/rts/build/libCffi_thr.a
* Raised the exception:
_cache/.shake.cache/5029bef81b20dfbd/0xF03C561F: getPermissions:getFileStatus: does not exist (No such file or directory)

$ ls -l _cache/.shake.cache/5029bef81b20dfbd/0xF03C561F
lrwxrwxrwx 2 david david 9 Jun 11 16:54 _cache/.shake.cache/5029bef81b20dfbd/0xF03C561F -> libCffi.a

_cache/.shake.cache/5029bef81b20dfbd/0xF03C561F is a broken link, but is "correct" in the sense that we want to copy the symlink as is so that _build/stage1/rts/build/libCffi_thr.a is a symlink to _build/stage1/rts/build/libCffi.a. This seems like a bug in Shake: it manages to correctly copy the symlink into the cache, but fails on the way back out.