help needed configuring GHC API client

[Norman Ramsey]

Alfredo,

I've confirmed that I can use the stage1 compiler and it doesn't
panic.

It occurs to me that I might be able to *compile* my code with the
stage1 compiler while using the bootstrap compiler and Haskell
Language Server.   I'll give that a shot.


Norman


 > 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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 > >
 >