shellFor: provide build tools for all packages when exactDeps = false

 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.

Author: jbgi

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 = {