Cleaning unnecessary Nix deps using remove-references-to

.gitignore

@@ -2,6 +2,7 @@ dist
 dist-*
 .ghc.environment.*
 result
+result-2
 .shake
 .neuron
 neuron.prof

ci.nix

@@ -1,11 +1,10 @@
 let
-  project = import ./project.nix { };
   pkgs = import <nixpkgs> { };
 in
 pkgs.recurseIntoAttrs {
   # Build both default.nix and shell.nix such that both derivations are
   # pushed to cachix. This allows the development workflow (bin/run, etc.) to
   # use cachix to full extent.
-  neuron = project.ghc.neuron;
-  neuronShell = project.shells.ghc;
+  neuron = import ./default.nix;
+  neuronShell = import ./shell.nix;
 }

default.nix

@@ -1 +1,23 @@
-(import ./project.nix {}).ghc.neuron
+let 
+  ghc = (import ./project.nix {}).ghc;
+  neuron = ghc.neuron;
+in 
+  neuron.overrideDerivation (drv: {
+    # Avoid transitive runtime dependency on the whole GHC distribution due to
+    # Cabal's `Path_*` module thingy. For details, see:
+    # https://github.com/NixOS/nixpkgs/blob/46405e7952c4b41ca0ba9c670fe9a84e8a5b3554/pkgs/development/tools/pandoc/default.nix#L13-L28
+    #
+    # In order to keep this list up to date, use nix-store and why-depends as
+    # explained here: https://www.srid.ca/04b88e01.html
+    disallowedReferences = [ ghc.pandoc ghc.pandoc-types ghc.shake ghc.warp ghc.HTTP ghc.js-jquery ghc.js-dgtable ghc.js-flot ];
+    postInstall = ''
+      remove-references-to -t ${ghc.pandoc} $out/bin/neuron
+      remove-references-to -t ${ghc.pandoc-types} $out/bin/neuron
+      remove-references-to -t ${ghc.shake} $out/bin/neuron
+      remove-references-to -t ${ghc.warp} $out/bin/neuron
+      remove-references-to -t ${ghc.HTTP} $out/bin/neuron
+      remove-references-to -t ${ghc.js-jquery} $out/bin/neuron
+      remove-references-to -t ${ghc.js-dgtable} $out/bin/neuron
+      remove-references-to -t ${ghc.js-flot} $out/bin/neuron
+    '';
+  })