Add support for GHC 9.12

[martijnbastiaan]

Closes #2930

Still TODO:

• Write a changelog entry (see changelog/README.md)
• Check copyright notices are up to date in edited files
• Fix issues exposed with cabal run -- clash-testsuite -p VACC -p VHDL -p clash
  • Do not pass deps to mkUnivCo ghc-typelits-natnormalise#88
• Fix issues exposed by cabal run -- clash-testsuite -p Numbers -p Strict
  • Good news: unrelated to typechecker business
  • Perhaps we shouldn't use newtype for any GHC version?
• Remove wrongly added changes to Add source for GHC 9.12 executable commit
• Find out how to remove {-# OPTIONS_GHC -Wno-deprecations #-} from clash-ghc/src-ghc/Clash/GHC/Util.hs
• Wait for GHC 9.12.3 9.12.4
  • Wait for https://gitlab.haskell.org/ghc/ghc/-/issues/26185
  • Wait for https://gitlab.haskell.org/ghc/ghc/-/issues/26711
  • Wait for Add metadata for 9.12.4 haskell/ghcup-metadata#373

[DigitalBrains1]

Could you add 9.12 to the README in the GHC compatibility section as part of this PR?

[kleinreact]

nix develop .#ghc9124 works for me using

$ nix flake update nixpkgs
$ cp nix/overlay-ghc910.nix nix/overlay-ghc912.nix
$ git add nix/overlay-ghc912.nix

with

--- a/flake.nix
+++ b/flake.nix
@@ -36,7 +36,7 @@
       # The versions of GHC that we want to be able to build / develop against
       # within the nix environment. Since nix is lazy, only derivations for
       # versions of GHC which are used are actually evaluated.
-      ghcVersions = [ "ghc967" "ghc984" "ghc9103" ];
+      ghcVersions = [ "ghc967" "ghc984" "ghc9103" "ghc9124" ];

       # We pick a single version of GHC to use by default within nix. This is
       # probably cleaner than always having N copies of each package / app and
--- a/nix/devshell.nix
+++ b/nix/devshell.nix
@@ -21,7 +21,7 @@ pkgs.mkShell {

   buildInputs = [
     clashPkgs.cabal-install
-    clashPkgs.haskell-language-server
+    #clashPkgs.haskell-language-server

     # https://discourse.nixos.org/t/non-interactive-bash-errors-from-flake-nix-mkshell/33310
     pkgs.bashInteractive
--- a/nix/overlay-ghc912.nix
+++ b/nix/overlay-ghc912.nix
@@ -11,6 +11,15 @@ in
   # brick 0.70.1 requires vty < 6.0.
   vty = doJailbreak (prev.callHackage "vty" "5.39" { });

+  # the selected defaults do not build with GHC 9.12.4
+  th-desugar = doJailbreak (prev.callHackage "th-desugar" "1.19" { });
+  singletons-th = doJailbreak (prev.callHackage "singletons-th" "3.5.1" { });
+  singletons-base = dontCheck (doJailbreak (prev.callHackage "singletons-base" "3.5" { }));
+  singletons-base-code-generator = markUnbroken prev.singletons-base-code-generator;
+  cabal-add = dontCheck prev.cabal-add;
+  statistics = dontCheck prev.statistics;
+  fourmolu = dontCheck prev.fourmolu;
+
   # Marked as broken in nixpkgs, since it specifies much older dependencies
   # than the defaults in nixpkgs.
   rewrite-inspector = doJailbreak (markUnbroken prev.rewrite-inspector);

Where I had to disable HLS, because one of it's dependencies ghcide runs into a GHC panic with 9.12.4. I would recommend to remove HLS from the default anyway, as it is not used by everyone and it can be still added as an extension like we do in clash-cores.

I recommend to add these changes as part of this PR as well.