Use runCommandLocal for dotCabal (#901)

This produces a pretty big store path (>1GB), and is very quick to
build. Prefer building it locally.

mk-local-hackage-repo/default.nix

@@ -17,7 +17,7 @@
 pkgs:
 { name, index }:
 
-pkgs.evalPackages.runCommand "hackage-repo-${name}" { nativeBuildInputs = [ pkgs.evalPackages.nix ]; } ''
+pkgs.evalPackages.runCommandLocal "hackage-repo-${name}" { nativeBuildInputs = [ pkgs.evalPackages.nix ]; } ''
 mkdir -p $out
 export expires="4000-01-01T00:00:00Z"
 

overlays/default.nix

@@ -17,6 +17,7 @@ let
     emscripten = import ./emscripten.nix;
     nix-prefetch-git-minimal = import ./nix-prefetch-git-minimal.nix;
     gobject-introspection = import ./gobject-introspection.nix;
+    shims = import ./shims.nix;
     eval-on-current = import ./eval-on-current.nix;
     eval-on-build = import ./eval-on-build.nix;
   };
@@ -48,6 +49,7 @@ let
     emscripten
     nix-prefetch-git-minimal
     gobject-introspection
+    shims
     # Restore nixpkgs haskell and haskellPackages
     (_: prev: { inherit (prev.haskell-nix-prev) haskell haskellPackages; })
   ];

overlays/haskell.nix

@@ -218,7 +218,8 @@ final: prev: {
               # dotCabalName anyway.
               dotCabalName = "dot-cabal-" + allNames;
             in
-            final.evalPackages.runCommand dotCabalName { nativeBuildInputs = [ cabal-install ]; } ''
+            # This is very big, and cheap to build: use runCommandLocal to prefer building it locally
+            final.evalPackages.runCommandLocal dotCabalName { nativeBuildInputs = [ cabal-install ]; } ''
                 mkdir -p $out/.cabal
                 cat <<EOF > $out/.cabal/config
                 ${final.lib.concatStrings (

overlays/shims.nix

@@ -0,0 +1,9 @@
+# Shims to make older versions of nixpkgs work
+final: prev: {
+  # nixpkgs 19.09 and older does not have runCommandLocal
+  runCommandLocal = prev.runCommandLocal or (name: env:
+    final.runCommand name ({
+      preferLocalBuild = true;
+      allowSubstitutes = false;
+    } // env));
+}