[DEVOPS-398] explorer frontend: add shell.nix for dev

Author: rvl

explorer/frontend/default.nix

@@ -40,19 +40,15 @@ let
 
   generatedSrc = pkgs.runCommand "cardano-sl-explorer-frontend-src" {
     inherit src bowerComponents;
-    buildInputs = [
-      oldHaskellPackages.purescript-derive-lenses
-      cardano-sl-explorer
-    ];
+    buildInputs = [ regen-script ];
   } ''
     cp -R --reflink=auto $src $out
     chmod -R u+w $out
     cd $out
     rm -rf .psci_modules .pulp-cache bower_components output result
 
     # Purescript code generation
-    cardano-explorer-hs2purs --bridge-path src/Generated/
-    scripts/generate-explorer-lenses.sh
+    regen
 
     # Frontend dependencies
     ln -s $bowerComponents/bower_components .
@@ -86,11 +82,21 @@ let
     nodejs = pkgs.nodejs-6_x;
   };
 
+  regen-script = pkgs.writeScriptBin "regen" ''
+    export PATH=${makeBinPath [oldHaskellPackages.purescript-derive-lenses cardano-sl-explorer]}:$PATH
+    cardano-explorer-hs2purs --bridge-path src/Generated/
+    scripts/generate-explorer-lenses.sh
+  '';
+
   frontend = { stdenv, python, purescript, mkYarnPackage }:
     mkYarnPackage {
       name = "cardano-explorer-frontend";
       src = generatedSrc;
-      extraBuildInputs = [ purescript ];
+      extraBuildInputs = [
+        purescript
+        regen-script
+      ];
+      passthru = { inherit bowerComponents; };
       installPhase = ''
         # run the build:prod script
         export PATH=$(pwd)/node_modules/.bin:$PATH

explorer/frontend/shell.nix

@@ -0,0 +1,29 @@
+{ ... }@args:
+
+let
+  cardanoPkgs = import ../.. args;
+  frontend = cardanoPkgs.cardano-sl-explorer-frontend;
+
+in
+  # fixme: cardano-sl-explorer source is not filtered enough, so
+  # generating files in frontend will cause a rebuild of explorer
+  # backend. You will just have to wait a little wait to get a shell.
+
+  frontend.overrideAttrs (oldAttrs: {
+
+    shellHook = ''
+      help() {
+        echo "*** To regenerate purescript code, run \`regen'."
+        echo
+        echo "*** To build, run \`yarn build:prod'."
+        echo "*** For dev, run \`yarn server:dev'."
+        echo
+        echo "*** To see this message again, run \`help'."
+      }
+
+      echo; echo; help
+
+      export PATH=$(pwd)/node_modules/.bin:$PATH
+    '';
+
+  })