rdmd -deps=foo.deps foo.d caching misses dependency on foo.deps #415

Transferred from: https://issues.dlang.org/show_bug.cgi?id=17071

User @timotheecour reported (2017-Jan-08 02:57:48):

$ rdmd -deps=foo.deps -c foo.d
#creates foo.deps foo.o
$ rm foo.deps

$ rdmd -deps=foo.deps -c foo.d
# BUG: foo.deps not recreated

$ rdmd --force -deps=foo.deps -c foo.d
#ok