Merge pull request #16 from mlabs-haskell/jared/postrebuild-package-lock-only-install

Update `package-lock.json` in `postRebuild` phase

Author: jaredponn

flake-lang/typescript/flake-typescript.nix

@@ -98,7 +98,6 @@ pkgs.lib.makeExtensible
                   ${pkgs.lib.escapeShellArg dataFolder} \
                   ${pkgs.lib.escapeShellArg dataLinkFarm}
 
-
               [[ -e ${pkgs.lib.escapeShellArg dataFolder} ]] && \
                   printf "flake-lang.nix: %s: removing existing \`%s\`\n" \
                       ${pkgs.lib.escapeShellArg name} \
@@ -126,6 +125,7 @@ pkgs.lib.makeExtensible
             cd $out
 
             ${builtins.concatStringsSep "\n" (builtins.map (dep: ''ln -sf ${pkgs.lib.escapeShellArg dep}/tarballs/* .'') npmExtraDependenciesTransitiveClosure)}
+
           '';
 
       # Shell script to create the dependencies copied in `npmExtraDependenciesTransitiveClosure`.
@@ -272,6 +272,34 @@ pkgs.lib.makeExtensible
           #     rm package-lock.json
           #   '';
           # ```
+          # NOTE(jaredponn): Yet another troubling note.. inspection of the
+          # code generated by `node2nix` makes it call `npm` install (unless
+          # otherwise specified) just after their `rebuildPhase`.
+          # Putting this here seems to "tell `npm` the complete picture" of the
+          # packages it can install, so it won't duplicate the local
+          # dependencies in the `node_modules` provided by nix multiple times.
+          # For example, if we have
+          #     - A depends on B
+          #     - B depends on C
+          # Then, without this, `npm` would create a dependency graph something
+          # like:
+          # ```
+          # A-B-C
+          #  `C
+          # ```
+          # instead of the more desirable
+          # ```
+          # A-B
+          #  `C
+          # ```
+          # Unfortunately, there is no trace of this in the documentation
+          # anywhere, and we only have some experimental evidence for this.
+          # Alternatively, we could just set the `dontNpmInstall` flag in
+          # node2nix, but I'm not sure of the consequences of that...
+          postRebuild =
+            ''
+              npm --offline --no-bin-links --ignore-scripts --package-lock-only install 
+            '';
         })
       ;