it probably shouldn't even tell me this at all, but certainly not twice.
to reproduce just have a 'package.yaml' file, and build the project once (so the .cabal is generated) then build the project again without changes; all that is emitted by stack is, say:
11:09 AM noon ∈ dev-dashboard>stack build
/home/noon/dev/dev-dashboard/dev-dashboard.cabal is up-to-date
/home/noon/dev/dev-dashboard/dev-dashboard.cabal is up-to-date
(edit): stack version:
11:33 AM noon ∈ dev-dashboard>stack --version
Version 1.0.5, Git revision 0ce4c9d51d830456e57a0da347fbb8971d3919ad x86_64