I'm confused about the meaning of -hidir and -i. Here's my experiment with both ghc-9.2.0 and ghc-8.10.4.

> $ find

> ./Main.hs
> ./lib/Lib.hs

>

> $ ghc -dynamic-too -c lib/Lib.hs -odir odir -hidir hidir_Lib

>

> $ ghc -dynamic-too -c Main.hs -odir odir -ihidir_Lib -hidir hidir_Main

>

> Main.hs:3:1: error:
>     Bad interface file: hidir_Main/Lib.hi
>         hidir_Main/Lib.hi: openBinaryFile: does not exist (No such file or directory)
>   |
> 3 | import Lib
>   | ^^^^^^^^^^

If I only use -hidir, it still fails with another error

> $ ghc -dynamic-too -c Main.hs -odir odir -hidir hidir_Lib

If I use both -i and -hidir pointing to the same folder, then it works!

> $ ghc -dynamic-too -c Main.hs -odir odir -ihidir_Lib -hidir hidir_Lib

Now, is this behavior a bug or a feature? And if it is a bug, what is the expected behavior?

Programs copied below.

Thank you!

Facundo

> $ cat lib/Lib.hs
> module Lib where
>
> f :: Int
> f = 1

>

> $ cat Main.hs
> {-# LANGUAGE TemplateHaskell #-}
>
> import Lib
> import Language.Haskell.TH
>
> main :: IO ()
> main = print $(runIO (print f) >> [| True |])