Stack init package not found

Question

When trying to build an existing project with Stack I got errors like

bv not found
- Genesis requires >=0.3 && <0.4 && -any
- exp requires -any

during stack init. The packages are all installed in a sandbox and are from hackage. I'm almost sure Stack doesn't look into the sandbox, but why can't it find the packages from hackage? I'm also able to build just by running cabal build.

Answer 1

stack does not look at Hackage at first. It tries to build your project using only packages from a snapshot of Stackage (you can find the exact snapshot you are using in the resolver field of stack.yaml). bv does not seem to be in Stackage (at least it is not in the latest LTS snapshot). Fortunately, the issue is easy to solve: just run stack solver --modify-stack-yaml. That will identify all non-Stackage dependencies and add them to the extra-deps field of stack.yaml. From that point on, those dependencies will be built somewhere in the .stack-work subdirectory of your project, in a very similar way to packages in a cabal-install sandbox.