GHCI needlessly recompiles sub-package

Question

I have a project (let's call it parent) that has a sub-package (child). Using HLS from emacs, whenever I change a file in the parent that imports part of the child package, and try to load it, GHCI will recompile the whole sub-package again every time. The sub-package has lots of TH code in it and takes a long time to compile, which really messes with your workflow when you just want to check if something works. Any ideas?

I'm using

• stack 2.7.5 with resolver lts-18.28
• cabal 3.6.2.0
• GHC 8.10.7
• HLS 1.7.0.0

My stack.yaml in the parent package:

resolver: lts-18.28

packages:
- .
- sub-package

extra-deps:
- ... (omitted)

allow-newer: true

EDIT: Minimal example: git repo

file details:

parent stack.yaml

resolver: lts-18.28

packages:
- .
- child

child stack.yaml

resolver: lts-18.28

packages:
- .

parent main src/Parent.hs:

module Parent where

import Child

someFunc :: IO ()
someFunc = childFunc

child main file child/src/Child.hs:

module Child where

childFunc :: IO ()
childFunc = putStrLn "someFunc"

Answer 1

Turns out adding -fobject-code to the .ghci file causes ghci to create object files, which in turn saves it the trouble of recompiling everything every time.

GHC reference