Try #1769:

Author: iohk-bors[bot]

builder/comp-builder.nix

@@ -239,9 +239,12 @@ let
   executableToolDepends =
     (lib.concatMap (c: if c.isHaskell or false
       then builtins.attrValues (c.components.exes or {})
-      else [c]) 
-      (builtins.filter (x: !(isNull x))
-      (map 
+      else [c])
+      (builtins.filter (x: !(isNull x)
+        # We always exclude hsc2hs from build-tools because it is unecessary as it is provided by ghc
+        # and hsc2hs from ghc is first in PATH so the one from build-tools is never used.
+        && x.identifier.name or "" != "hsc2hs")
+      (map
         (p: if builtins.isFunction p
           then p { inherit  (package.identifier) version; inherit revision; }
           else p) build-tools))) ++
@@ -328,7 +331,7 @@ let
     outputHashMode = "recursive";
     outputHashAlgo = "sha256";
   };
-                    
+
   drv = stdenv.mkDerivation (commonAttrs // contentAddressedAttrs // {
     pname = nameOnly;
     inherit (package.identifier) version;

builder/shell-for.nix

@@ -67,6 +67,8 @@ let
   selectedComponents =
     lib.filter isSelectedComponent  (lib.attrValues transitiveDependenciesComponents);
 
+  allHsPkgsComponents = lib.concatMap haskellLib.getAllComponents (builtins.attrValues hsPkgs);
+
   # Given a list of `depends`, removes those which are selected components
   removeSelectedInputs =
     lib.filter (input: !(isSelectedComponent input));
@@ -105,7 +107,10 @@ let
   systemInputs = removeSelectedInputs (uniqueWithName allSystemInputs);
 
   nativeBuildInputs = removeSelectedInputs
-    (lib.concatMap (c: c.executableToolDepends) selectedComponents);
+    (uniqueWithName (lib.concatMap (c: c.executableToolDepends)
+      # When not using `exactDeps` cabal may try to build arbitrary dependencies
+      # so in this case we need to provide the build tools for all of hsPkgs:
+      (if exactDeps then selectedComponents else allHsPkgsComponents)));
 
   # Set up a "dummy" component to use with ghcForComponent.
   component = {