Try latest cabal for haddocks

.github/workflows/github-page.yml

@@ -2,8 +2,9 @@ name: "Haddock documentation"
 
 on:
   push:
-    branches:
-      - main
+    # FIXME uncomment prior to merge
+    # branches:
+    #   - main
 
 jobs:
   build:

flake.nix

@@ -25,6 +25,29 @@
       # "aarch64-linux" - disable these temporarily because the build is broken
       # "aarch64-darwin" - disable these temporarily because the build is broken
     ];
+
+    # see flake `variants` below for alternative compilers
+    defaultCompiler = "ghc965";
+    haddockShellCompiler = defaultCompiler;
+
+    cabalHeadOverlay = final: prev:
+    {
+      cabal-head = (final.haskell-nix.cabalProject {
+        # cabal master commit containing https://github.com/haskell/cabal/pull/8726
+        src = final.fetchFromGitHub {
+          owner = "haskell";
+          repo = "cabal";
+          rev = "6eaba73ac95c62f8dc576e227b5f9c346910303c";
+          hash = "sha256-Uu/w6AK61F7XPxtKe+NinuOR4tLbaT6rwxVrQghDQjo=";
+        };
+        index-state = "2024-07-03T00:00:00Z";
+        compiler-nix-name = haddockShellCompiler;
+        cabalProject = ''
+        packages: Cabal-syntax Cabal cabal-install-solver cabal-install
+        '';
+        configureArgs = "--disable-benchmarks --disable-tests";
+      }).cabal-install.components.exes.cabal;
+    };
   in
     inputs.flake-utils.lib.eachSystem supportedSystems (
       system: let
@@ -38,15 +61,13 @@
             inputs.haskellNix.overlay
             # configure haskell.nix to use iohk-nix crypto librairies.
             inputs.iohkNix.overlays.haskell-nix-crypto
+            cabalHeadOverlay
           ];
           inherit system;
           inherit (inputs.haskellNix) config;
         };
         inherit (nixpkgs) lib;
 
-        # see flake `variants` below for alternative compilers
-        defaultCompiler = "ghc964";
-        haddockShellCompiler = defaultCompiler;
         # We use cabalProject' to ensure we don't build the plan for
         # all systems.
         cabalProject = nixpkgs.haskell-nix.cabalProject' ({config, ...}: {
@@ -87,7 +108,7 @@
               stylish-haskell = "0.14.5.0";
             };
           # and from nixpkgs or other inputs
-          shell.nativeBuildInputs = with nixpkgs; [ gh jq yq-go actionlint shellcheck ];
+          shell.nativeBuildInputs = with nixpkgs; [ gh jq yq-go actionlint shellcheck cabal-head ];
           # disable Hoogle until someone request it
           shell.withHoogle = false;
           # Skip cross compilers for the shell