Meaning of -i and -hidir

[Ryan Yates]

The behavior of `-hidir` and `-i` changed in response to this issue:

https://gitlab.haskell.org/ghc/ghc/-/issues/16500

We just ran into this and I think the change is unfortunate.  I don't think
`-hidir` (a flag about output) should override the input search flag.  I
would like it to at least merge the two so it searches both the `-hidir`
and the `-i`s rather than overriding.  Reverting the change would be fine
too (I think) because you can always specify the same path as `-hidir` and
`-i`.  As it is now, you can control *both* the input and the output.

On Sat, Oct 23, 2021 at 4:26 PM Carter Schonwald <carter.schonwald at gmail.com>
wrote:

> Could be!  I’m far from a computer much of this week
>
> On Sat, Oct 23, 2021 at 2:36 PM Brandon Allbery <allbery.b at gmail.com>
> wrote:
>
>> I would expect that to be -I and for -i to specify module paths (which
>> might well mean .hi).
>>
>> On Sat, Oct 23, 2021 at 2:32 PM Carter Schonwald <
>> carter.schonwald at gmail.com> wrote:
>>
>>> I would assume the -i is for include c header search paths but I
>>> could be wrong
>>>
>>> On Sat, Oct 23, 2021 at 6:00 AM Oleg Grenrus <oleg.grenrus at iki.fi>
>>> wrote:
>>>
>>>> This looks like a bug.
>>>>
>>>> -hidir documentation says
>>>>
>>>> > Redirects all generated interface files into ⟨dir⟩, instead of the
>>>> default.
>>>> > Please also note that when doing incremental compilation (by ghc
>>>> --make or ghc -c), this directory is where GHC looks into to find interface
>>>> files.
>>>>
>>>> And documentation for -i doesn't mention looking for interface files.
>>>>
>>>> So by doing
>>>>
>>>> % ghc -dynamic-too -c lib/Lib.hs -odir odir -hidir hidir_Lib
>>>> % ghc -dynamic-too -c Main.hs -odir odir -hidir hidir_Main -ihidir_Lib
>>>> 1
>>>> % ghc odir/Lib.o odir/Main.o -o Demo
>>>> % ./Demo
>>>> True
>>>>
>>>> everything compiles, TH is run, and demo works. The result files are
>>>>
>>>> % find .
>>>> .
>>>> ./Demo
>>>> ./Main.hs
>>>> ./hidir_Main
>>>> ./hidir_Main/Main.dyn_hi
>>>> ./hidir_Main/Main.hi
>>>> ./odir
>>>> ./odir/Main.dyn_o
>>>> ./odir/Main.o
>>>> ./odir/Lib.dyn_o
>>>> ./odir/Lib.o
>>>> ./hidir_Lib
>>>> ./hidir_Lib/Lib.dyn_hi
>>>> ./hidir_Lib/Lib.hi
>>>> ./lib
>>>> ./lib/Lib.hs
>>>>
>>>> ---
>>>>
>>>> The confusing error is caused by Lib module in libiserv:
>>>> https://hackage.haskell.org/package/libiserv
>>>> which GHC picks!
>>>>
>>>> If we rename your Lib module to Library, the error is way better: Could
>>>> not find module ‘Library’
>>>>
>>>> I also tried using same -hidir when compiling both modules, then GHC
>>>> still cannot find the Library interface, even the documentation says it
>>>> should.
>>>>
>>>> Please open a GHC issue at https://gitlab.haskell.org/ghc/ghc/-/issues
>>>>
>>>>
>>>>
>>>> - Oleg
>>>> On 22.10.2021 19.16, Domínguez, Facundo wrote:
>>>>
>>>> Dear devs,
>>>>
>>>> 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
>>>> >
>>>> > Main.hs:7:29: error: Variable not in scope: f
>>>> >   |
>>>> > 7 | main = print $(runIO (print f) >> [| True |])
>>>> >   |                             ^
>>>>
>>>> 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 <http://language.haskell.th/>
>>>> >
>>>> > main :: IO ()
>>>> > main = print $(runIO (print f) >> [| True |])
>>>>
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>>
>>
>> --
>> brandon s allbery kf8nh
>> allbery.b at gmail.com
>>
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