Build dynamic executables by default on supported platforms

[pepeiborra]

We want A)git clone .. && cd <dir> && cabal install haskell-language-server to build a -dynamic binary by default on Linux, MacOs and any other supported platforms, excluding Windows, for the reasons outlined in https://github.com/haskell/haskell-language-server/blob/1ba88ab9eca1da29cd4fee7d2084eba4074fbe47/docs/troubleshooting.md#problems-with-dynamic-linking

Similarly, we also want B)cabal unpack haskell-language-server && cd <dir> && cabal install to build dynamic executables.

What's the best way to do this? Summarising the discussion at https://gitlab.haskell.org/haskell/ghcup-hs/-/issues/245:

1. A cabal.project setting is not a good fit since conditionals are not supported and would not help with B)
2. A conditional ghc-options: -dynamic in haskell-language-server.cabal doesn't play well with cabal v2-build
3. A cabal-dynamic.project.local file would require an extra step and would not help with B) either

[pepeiborra]

Summoning Cabal experts, @emilypi @phadej any suggestions?

[jneira]

A conditional ghc-options: -dynamic in haskell-language-server.cabal doesn't play well with cabal v2-build

hmm could you describe briefly what would be the problem?

if !os(windows) && !flag(static)
  ghc-options: -dynamic

would be a reasonable way to do it

[jneira]

Want to link a closed issue which considered build dinamically prebuilt binaries: #2069
And i dont find it right now but i want to remember someone had problems in linux building using stack and dynamic linking enabled.

[pepeiborra]

A conditional ghc-options: -dynamic in haskell-language-server.cabal doesn't play well with cabal v2-build

hmm could you describe briefly what would be the problem?

if !os(windows) && !flag(static)
  ghc-options: -dynamic

would be a reasonable way to do it

This doesn't work well for the reasons outlined in https://gitlab.haskell.org/haskell/ghcup-hs/-/issues/245#note_378797

[pepeiborra]

Want to link a closed issue which considered build dinamically prebuilt binaries: #2069
And i dont find it right now but i want to remember someone had problems in linux building using stack and dynamic linking enabled.

Thanks but the linked issue is about distribution, this issue is about building from source.

[hasufell]

A conditional ghc-options: -dynamic in haskell-language-server.cabal doesn't play well with cabal v2-build

hmm could you describe briefly what would be the problem?

if !os(windows) && !flag(static)
  ghc-options: -dynamic

would be a reasonable way to do it

This doesn't work well for the reasons outlined in https://gitlab.haskell.org/haskell/ghcup-hs/-/issues/245#note_378797

The isssue I described is orthogonal to where this flag is put, be it cabal file, project file or command line. The problem is that we need to install the plugin libs, which requires v2-install, which doesn't play nice with compiling from git, because of overly eager cache hits.

[jneira]

We took the path of building fully statically linked binaries for linux and set a warning for macos, suggesting building dinamically from source,
Otoh ghcup has a better support to build hls dinamically and https://gitlab.haskell.org/haskell/ghcup-hs/-/issues/245 is closed
@pepeiborra do you think could we close this?

[pepeiborra]

No, I still want cabal install HLS to build a dyn linked binary by default