haskell-language-server throws "this operation requires -fexternal-interpreter"

[maksbotan]

I use ghc 8.10.7 from haskell.nix (commit 5a310b0) and haskell-language-server 1.7.0.0 built with haskell-nix.cabalProject from github release tarball.

When running haskell-language-server from CLI or through my editor, I get this error for every file:

Message:  haskell-language-server: this operation requires -fexternal-interpreter

I've reported this to haskell-language-server at haskell/haskell-language-server#2975, but turns out that this is probably compiler-related.

Quoting @wz1000:

In the GHC 8.10.7 source code, this error is only reachable if the HAVE_INTERNAL_INTERPRETER flag is unset when GHC was built: https://gitlab.haskell.org/ghc/ghc/-/blob/ghc-8.10.7-release/compiler/ghci/GHCi.hs#L163

Curiously, with haskell.nix 6d6df80 everything works.

I will try to bisect, if it gives something, I'll update here.

[maksbotan]

git bisect points to this commit: 95faec6

[blaxill]

I'm also seeing this with latest haskell.nix GHC 9.* (macos)

[hamishmack]

This should be fixed by #1520.

[blaxill]

@hamishmack this is now working for ghc 9.0.2, but oddly not for ghc 9.2.3 (at least for me) perhaps an hls upstream issue though

[kokobd]

I'm also seeing this on ghc 9.2.3. From hackage, we can see ghc 9.2.2 has a flag internal-interpreter (in ghc, not ghci), while ghc-9.0.2 has a different flag ghci. #1520 only sets ghci to true.