bar-bar.cabal

cabal-version: 2.2
name:          bar
version:       0

library
  default-language:   Haskell2010
  build-tool-depends: foo:foo -any
  exposed-modules:    Bar
  build-depends:
    , base
    , process
    , template-haskell

bar-Bar.hs

{-# LANGUAGE TemplateHaskell #-}
module Bar where

import System.Process (readProcess)
import Control.Monad.IO.Class (liftIO)
import Language.Haskell.TH.Syntax (lift)

fooBar :: String
fooBar = $(liftIO (readProcess "foo" [] "") >>= lift)

cabal.project

packages: foo bar

foo-foo.cabal

cabal-version: 2.2
name:          foo
version:       0

library
  default-language:   Haskell2010
  build-tool-depends: foo:foo -any
  exposed-modules:    Foo
  build-depends:
    , base
    , process
    , template-haskell

executable foo
  default-language: Haskell2010
  scope:            private
  main-is:          FooExe.hs
  build-depends:    base

foo-Foo.hs

{-# LANGUAGE TemplateHaskell #-}
module Foo where

import System.Process (readProcess)
import Control.Monad.IO.Class (liftIO)
import Language.Haskell.TH.Syntax (lift)

fooFoo :: String
fooFoo = $(liftIO (readProcess "foo" [] "") >>= lift)

foo-FooExe.hs

data Main (main) where

main :: IO ()
main = putStrLn "foo-executable"