Split web common (#2611)

There is code that is shared between plutus playground and plutus SCB that is not used by marlowe playground or marlowe dashboard. The same will be true for Marlowe once SCP-1672 is implemented. There is also code that is useful to all web projects. We wouldn't normally mind mixing these 3 types in one location however some of the purescript code depends on code generated by the psgenerator scripts. If we have them all together we have to add lots of superfluous types to our psgenerators. It started to get our of hand when I looked at implementing SCP-1672. This commit splits these 3 types into 3 different directories and should allow the psgenerator scripts to be simplified.

web-common-marlowe doesn't have anything in it yet but it will do with SCP-1672

Currently we're sticking with the model of "add an extra source directory" rather than having full on purescript or node modules. This is because it's currently much simpler, also spago2nix can't handle local modules yet (justinwoo/spago2nix#19). Finally, it makes it much easier to make changes to web-common and web-common-* during development of the main client projects because they are symlinks in the project, this means (in VSCode at least) that intellisense etc work perfectly.

nix/lib/purescript.nix

@@ -4,9 +4,7 @@
 , nix-gitignore
 }:
 
-{
-  # path to generated purescript sources
-  psSrc
+{ pkgs
   # path to project sources
 , src
   # name of the project
@@ -15,8 +13,8 @@
 , packages
   # spago packages as generated by spago2nix
 , spagoPackages
-  # web-common project
-, webCommon
+  # a map of source directory name to contents that will be symlinked into the environment before building
+, extraSrcs ? { }
   # node_modules to use
 , nodeModules
   # control execution of unit tests
@@ -26,6 +24,9 @@ let
   # Cleans the source based on the patterns in ./.gitignore and the additionalIgnores
   cleanSrcs = nix-gitignore.gitignoreSource [ "/*.adoc" "/*.nix" ] src;
 
+  addExtraSrc = k: v: "ln -sf ${v} ${k}";
+  addExtraSrcs = builtins.concatStringsSep "\n" (builtins.attrValues (pkgs.lib.mapAttrs addExtraSrc extraSrcs));
+  extraPSPaths = builtins.concatStringsSep " " (map (d: "${d}/**/*.purs") (builtins.attrNames extraSrcs));
 in
 stdenv.mkDerivation {
   inherit name checkPhase;
@@ -35,11 +36,10 @@ stdenv.mkDerivation {
     export HOME=$NIX_BUILD_TOP
     shopt -s globstar
     ln -s ${nodeModules}/node_modules node_modules
-    ln -s ${psSrc} generated
-    ln -sf ${webCommon} web-common
-
+    ${addExtraSrcs}
+    ls generated
     sh ${spagoPackages.installSpagoStyle}
-    sh ${spagoPackages.buildSpagoStyle} src/**/*.purs test/**/*.purs generated/**/*.purs web-common/**/*.purs
+    sh ${spagoPackages.buildSpagoStyle} src/**/*.purs test/**/*.purs ${extraPSPaths}
     ${nodejs}/bin/npm run webpack
   '';
   doCheck = true;