haskell.packages.{ghc96,ghc98}.haskell-language-server: fix build

pkgs/development/haskell-modules/configuration-ghc-9.6.x.nix

@@ -216,6 +216,10 @@ in
         hls_overlay = lself: lsuper: {
           Cabal-syntax = lself.Cabal-syntax_3_10_3_0;
           Cabal = lself.Cabal_3_10_3_0;
+          # Test suite can't find executable due to https://github.com/haskell/cabal/issues/11598
+          cabal-add = dontCheck lsuper.cabal-add_0_2;
+          # Cabal-syntax >=3.14.2.0, tar <0.7
+          cabal-install-parsers = doJailbreak lsuper.cabal-install-parsers;
           extensions = dontCheck (doJailbreak lself.extensions_0_1_0_1);
         };
       in

pkgs/development/haskell-modules/configuration-ghc-9.8.x.nix

@@ -120,6 +120,10 @@ in
         hls_overlay = lself: lsuper: {
           Cabal-syntax = lself.Cabal-syntax_3_10_3_0;
           Cabal = lself.Cabal_3_10_3_0;
+          # Test suite can't find executable due to https://github.com/haskell/cabal/issues/11598
+          cabal-add = dontCheck lsuper.cabal-add_0_2;
+          # Cabal-syntax >=3.14.2.0, tar <0.7
+          cabal-install-parsers = doJailbreak lsuper.cabal-install-parsers;
           extensions = dontCheck (doJailbreak lself.extensions_0_1_0_1);
         };
       in

pkgs/development/haskell-modules/configuration-hackage2nix/main.yaml

@@ -72,6 +72,7 @@ extra-packages:
   - Cabal == 3.12.*
   - Cabal == 3.14.*
   - Cabal == 3.16.*                     # version required for cabal-install and other packages
+  - cabal-add < 0.2.1                   # 2026-09-05: required for HLS with GHC <= 9.8
   - cabal-install == 3.14.*             # 2026-07-26: required to match Cabal used when building HLS
   - cabal-install-solver == 3.14.*      # 2026-07-26: required to build cabal-install 3.14
   - Cabal-syntax == 3.6.*               # required for the GHC 9.0.2 package set

pkgs/development/haskell-modules/hackage-packages.nix

@@ -126754,6 +126754,69 @@ self: {
     }
   ) { youProbablyWantCapitalCabal = null; };
 
+  cabal-add_0_2 = callPackage (
+    {
+      mkDerivation,
+      base,
+      bytestring,
+      Cabal,
+      cabal-install-parsers,
+      Cabal-syntax,
+      containers,
+      Diff,
+      directory,
+      filepath,
+      mtl,
+      optparse-applicative,
+      process,
+      string-qq,
+      tasty,
+      temporary,
+    }:
+    mkDerivation {
+      pname = "cabal-add";
+      version = "0.2";
+      sha256 = "0fd098gkfmxrhq0k4j1ll5g4xwwzgmhdx0mj9hnp5xanj7z1laxg";
+      revision = "1";
+      editedCabalFile = "03z75dp7mf471mm40mfb157ng2fgp66nkyhaa6fsb3j2qfwg5wz4";
+      isLibrary = true;
+      isExecutable = true;
+      libraryHaskellDepends = [
+        base
+        bytestring
+        Cabal
+        Cabal-syntax
+        containers
+        mtl
+      ];
+      executableHaskellDepends = [
+        base
+        bytestring
+        cabal-install-parsers
+        Cabal-syntax
+        directory
+        filepath
+        optparse-applicative
+        process
+      ];
+      testHaskellDepends = [
+        base
+        bytestring
+        Cabal
+        Diff
+        directory
+        process
+        string-qq
+        tasty
+        temporary
+      ];
+      description = "Extend Cabal build-depends from the command line";
+      license = lib.meta.getLicenseFromSpdxId "BSD-3-Clause";
+      hydraPlatforms = lib.platforms.none;
+      mainProgram = "cabal-add";
+    }
+  ) { };
+
   cabal-add = callPackage (
     {
       mkDerivation,