help needed configuring GHC API client

[Alfredo Di Napoli]

Hi Norman,

in addition to what Ben already said: is there any particular reason you
wanted to use the stage0 compiler? I have written a small program against
HEAD which used the GHC API fairly recently, and I have simply used the
`stage1` compiler. An excerpt from my little code snippet:

```
-- This is just the output of '_build/stage1/bin/ghc --print-libdir'
myGhcLibDir :: FilePath
myGhcLibDir = "./_build/stage1/lib"

playground :: FilePath -> IO ()
playground fn = do
  res <- runGhc (Just myGhcLibDir) $ do
  ...
```

As you can see that's exactly what you are doing, modulo the fact I was
using the `stage1` (where _build is the default directory for Hadrian
builds).

Hope this helps in some way!

A.




On Fri, 24 Sept 2021 at 03:37, Ben Gamari <ben at smart-cactus.org> wrote:

> Norman Ramsey <nr at cs.tufts.edu> writes:
>
> > I'm writing client code against the GHC API in HEAD (version 9.3),
> > using 9.0.1 as my bootstrap compiler.  To make it possible to build
> > this code, I've set up cabal using
> >
> >    cabal v1-configure \
> >       --package-db clear \
> >       --package-db $STAGE0/lib/package.conf.d/      # stage0 libraries
> >
> > In my Haskell code I'm invoking `runGhc (Just thelibdir)` where
> >
> >    thelibir = "/home/nr/asterius/ghc/_build/stage0/lib"
> >
> > which is my `$STAGE0/lib`.
> >
> > Unfortunuately, when I launch my app, `setSessionDynFlags` panics.
> > The output, along with some diagnostic information about some dflags
> > that seemed relevant, looks like this:
> >
> >   libdir = /home/nr/asterius/ghc/_build/stage0/lib
> >   includePaths = IncludeSpecs {includePathsQuote = [],
> includePathsGlobal = [], includePathsQuoteImplicit = []}
> >   libraryPaths = []
> >   packageDBFlags = []
> >   packageEnv = Nothing
> >   panic! (the 'impossible' happened)
> >     GHC version 9.3.20210918:
> >           GHC couldn't find the RTS constants (#define HS_CONSTANTS ")
> in /home/nr/.ghcup/ghc/9.0.1/lib/ghc-9.0.1/include/DerivedConstants.h: the
> RTS package you are trying to use is perhaps for another GHC version(e.g.
> you are using the wrong package database) or the package database is broken.
> >
> >   CallStack (from HasCallStack):
> >     error, called at
> _build/stage0/compiler/build/GHC/Platform/Constants.hs:143:20 in
> ghc:GHC.Platform.Constants
> >
> >   Please report this as a GHC bug:
> https://www.haskell.org/ghc/reportabug
> >
> > I'm a little suprprised that my app is hunting for 9.3 information in
> > the tree that belongs to the bootstrap compiler.
> >
> I suspect that the stages are getting mixed up here. Would it be
> possible to post a full reproducer? I'd be happy to investigate further,
> but without being able to reproduce locally it's a bit hard to say
> anything useful. My recollection is that we look for DerivedConstants.h
> in the usual include paths, so there are many ways in which things could
> go wrong.
>
> Cheers,
>
> - Ben
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