First attempt at getting haskell.nix to work with nixpkgs provided compiler

builder/hspkg-builder.nix

@@ -18,10 +18,6 @@ config:
 , ...
 }@pkg:
 
-assert (if ghc.isHaskellNixCompiler or false then true
-  else throw ("It is likely you used `haskell.compiler.X` instead of `haskell-nix.compiler.X`"
-    + pkgs.lib.optionalString (name != null) (" for " + name)));
-
 let
   # Some packages bundled with GHC are not the same as they are in hackage.
   bundledSrc = {

lib/call-cabal-project-to-nix.nix

@@ -107,9 +107,6 @@ let
               pkgs.haskell-nix.compiler."${compiler-nix-name}";
 
 in
-  assert (if ghc'.isHaskellNixCompiler or false then true
-    else throw ("It is likely you used `haskell.compiler.X` instead of `haskell-nix.compiler.X`"
-      + forName));
 
 let
   ghc = ghc';

test/with-nixpkgs-ghc/default.nix

@@ -0,0 +1,86 @@
+{ with-nixpkgs ? true }:
+let
+
+  haskell-nix = import ../../default.nix { };
+  nixpkgs = haskell-nix.inputs.nixpkgs.outPath;
+
+  fix = final: prev: compiler-nix-name:
+    let
+      haskell-nix-ghc = prev.haskell-nix.compiler.${compiler-nix-name};
+      nixpkgs-ghc = prev.haskell.compiler.${compiler-nix-name};
+
+      exactDepOut =
+        pkgs.runCommand "${nixpkgs-ghc.name}-exactDeps" { }
+          ''
+            mkdir -p $out
+            ${nixpkgs-ghc}/bin/ghc-pkg --version
+            for P in $(${nixpkgs-ghc}/bin/ghc-pkg list --simple-output | sed 's/-[0-9][0-9.]*//g'); do
+              mkdir -p $out/exactDeps/$P
+              touch $out/exactDeps/$P/configure-flags
+              touch $out/exactDeps/$P/cabal.config
+
+              if id=$(${nixpkgs-ghc}/bin/ghc-pkg field $P id --simple-output); then
+                echo "--dependency=$P=$id" >> $out/exactDeps/$P/configure-flags
+              elif id=$(${nixpkgs-ghc}/bin/ghc-pkg field "z-$P-z-*" id --simple-output); then
+                name=$(${nixpkgs-ghc}/bin/ghc-pkg field "z-$P-z-*" name --simple-output)
+                # so we are dealing with a sublib. As we build sublibs separately, the above
+                # query should be safe.
+                echo "--dependency=''${name#z-$P-z-}=$id" >> $out/exactDeps/$P/configure-flags
+              fi
+              if ver=$(${nixpkgs-ghc}/bin/ghc-pkg field $P version --simple-output); then
+                echo "constraint: $P == $ver" >> $out/exactDeps/$P/cabal.config
+                echo "constraint: $P installed" >> $out/exactDeps/$P/cabal.config
+              fi
+            done
+
+            mkdir -p $out/evalDeps
+            for P in $(${nixpkgs-ghc}/bin/ghc-pkg list --simple-output | sed 's/-[0-9][0-9.]*//g'); do
+              touch $out/evalDeps/$P
+              if id=$(${nixpkgs-ghc}/bin/ghc-pkg field $P id --simple-output); then
+                echo "package-id $id" >> $out/evalDeps/$P
+              fi
+            done
+          '';
+    in
+    pkgs.symlinkJoin {
+      paths = [ nixpkgs-ghc exactDepOut ];
+
+      name = "${nixpkgs-ghc.name}-with-evalDeps";
+      inherit (nixpkgs-ghc) version;
+
+      # BLAH
+      inherit (haskell-nix-ghc) passthru;
+      # enableShared = true;
+      # targetPrefix = "";
+      # passthru.configured-src = haskell-nix-ghc.passthru.configured-src;
+      # useLLVM = false;
+    };
+
+  o2 = (
+    final: prev: {
+      haskell-nix = prev.haskell-nix // {
+        compiler = prev.haskell-nix.compiler // {
+          ghc8107 = fix final prev "ghc8107";
+        };
+      };
+    }
+  );
+
+  pkgs = import nixpkgs {
+    inherit (haskell-nix) config;
+    overlays = [
+      haskell-nix.overlay
+    ]
+    ++
+    (if with-nixpkgs then [ o2 ] else [ ])
+    ;
+  };
+
+  prj = pkgs.haskell-nix.cabalProject {
+    src = ./empty;
+    cabalProject = "extra-packages: lens";
+    compiler-nix-name = "ghc8107";
+  };
+in
+
+prj.plan-nix