Regenerate the files transparently when entering the dev shell

Removes the need from running `regenerate-files` manually

doc/filegen.md

@@ -29,7 +29,10 @@ This has two main advantages:
 
 ## Usage
 
-To re-generate the files run:
+The files specified in `files.*` are regenerated automatically when entering
+the devshell (unless `filegen_hook` is set to false).
+
+They can also be regenerated manually with:
 
 ```bash
 nix run .#regenerate-files

lib/files.ncl

@@ -83,10 +83,31 @@ let regenerate_files | Files -> nix.derivation.Derivation = fun files_to_generat
         Set of files that should be generated in the project's directory.
       "%
       = {},
+    filegen_hook.enable
+      | Bool
+      | doc m%"
+        Enable a hook that will automatically regenerate the files managed by
+        Nickel when entering the shell.
+      "%
+      | default
+      = true,
     flake.apps, # Forward declaration. Not great but would need some refactor to fix
+    shells,
   },
   config | Schema = {
       files,
+      filegen_hook,
+      shells,
       flake.apps.regenerate-files.program = nix-s%"%{regenerate_files files}/bin/regenerate-files"%,
+
+      shells.build.hooks =
+        if filegen_hook.enable then
+          {
+            filegen_hook = nix-s%"
+            %{regenerate_files files}/bin/regenerate-files
+          "%
+          }
+        else
+          {},
     },
 }

run-test.sh

@@ -120,7 +120,6 @@ test_example () (
   cp -r "$examplePath" ./example
   pushd ./example
   prepare_shell
-  nix run .\#regenerate-files --print-build-logs
   nix develop --print-build-logs --command bash test.sh
   popd
   popd