Automatic flags are not automatic in stack. So we have to manually specify them for each gi-* package. I think it might be possible to work around this by eliminating the enable-overloading cabal flag.

Haskell gi-*.cabal files contain:

if flag(enable-overloading)
     cpp-options: -DENABLE_OVERLOADING
     build-depends: haskell-gi-overloading == 1.0.*
else
     build-depends: haskell-gi-overloading == 0.0

We could change this to just:

build-depends: haskell-gi-overloading < 1.1

and replace ENABLE_OVERLOADING with haskell-gi-overloading_MIN_VERSION(1,0)

Instead of -f-enable-overloading we would need to use --constraint=haskell-gi-overloading==0.0.

In stack.yaml just having

extra-deps:
- haskell-gi-overloading-0.0

Would be enough to switch off overloading.

Another option might be to keep the enable-overloading flag but only on one package (perhaps haskell-gi). So haskell-gi.cabal would have the automatic flag and:

if flag(enable-overloading)
     cpp-options: -DENABLE_OVERLOADING
     build-depends: haskell-gi-overloading == 1.0.*
else
     build-depends: haskell-gi-overloading == 0.0

While all the gi-*.cabal files would have:

build-depends: haskell-gi-overloading < 1.1

and use haskell-gi-overloading_MIN_VERSION(1,0). The stack.yaml would be:

extra-deps:
- haskell-gi-overloading-0.0

flags:
  haskell-gi:
    enable-overloading: false

This is not quite as nice.

CC @mgsloan