Make experimental-features a proper type

Rather than having them plain strings scattered through the whole
codebase, create an enum containing all the known experimental features.

This means that
- Nix can now `warn` when an unkwown experimental feature is passed
  (making it much nicer to spot typos and spot deprecated features)
- It’s now easy to remove a feature altogether (once the feature isn’t
  experimental anymore or is dropped) by just removing the field for the
  enum and letting the compiler point us to all the now invalid usages
  of it.

5 files changed, 5 insertions, 5 deletions

diff --git a/src/nix/develop.cc b/src/nix/develop.cc
index f22335023..5aad53919 100644
--- a/src/nix/develop.cc
+++ b/src/nix/develop.cc
@@ -195,7 +195,7 @@ static StorePath getDerivationEnvironment(ref<Store> store, ref<Store> evalStore
        'buildDerivation', but that's privileged. */
     drv.name += "-env";
     drv.inputSrcs.insert(std::move(getEnvShPath));
-    if (settings.isExperimentalFeatureEnabled("ca-derivations")) {
+    if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations)) {
         for (auto & output : drv.outputs) {
             output.second = {
                 .output = DerivationOutputDeferred{},
diff --git a/src/nix/flake.cc b/src/nix/flake.cc
index 7e4d23f6e..68bb76742 100644
--- a/src/nix/flake.cc
+++ b/src/nix/flake.cc
@@ -1138,7 +1138,7 @@ struct CmdFlake : NixMultiCommand
     {
         if (!command)
             throw UsageError("'nix flake' requires a sub-command.");
-        settings.requireExperimentalFeature("flakes");
+        settings.requireExperimentalFeature(Xp::Flakes);
         command->second->prepare();
         command->second->run();
     }
diff --git a/src/nix/main.cc b/src/nix/main.cc
index 2c3976689..1e033f4f2 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -337,7 +337,7 @@ void mainWrapped(int argc, char * * argv)
     if (args.command->first != "repl"
         && args.command->first != "doctor"
         && args.command->first != "upgrade-nix")
-        settings.requireExperimentalFeature("nix-command");
+        settings.requireExperimentalFeature(Xp::NixCommand);
 
     if (args.useNet && !haveInternet()) {
         warn("you don't have Internet access; disabling some network-dependent features");
diff --git a/src/nix/realisation.cc b/src/nix/realisation.cc
index dfa8ff449..c9a7157cd 100644
--- a/src/nix/realisation.cc
+++ b/src/nix/realisation.cc
@@ -46,7 +46,7 @@ struct CmdRealisationInfo : BuiltPathsCommand, MixJSON
 
     void run(ref<Store> store, BuiltPaths && paths) override
     {
-        settings.requireExperimentalFeature("ca-derivations");
+        settings.requireExperimentalFeature(Xp::CaDerivations);
         RealisedPath::Set realisations;
 
         for (auto & builtPath : paths) {
diff --git a/src/nix/sigs.cc b/src/nix/sigs.cc
index 43e0d9148..6a238efbe 100644
--- a/src/nix/sigs.cc
+++ b/src/nix/sigs.cc
@@ -219,7 +219,7 @@ struct CmdKey : NixMultiCommand
     {
         if (!command)
             throw UsageError("'nix flake' requires a sub-command.");
-        settings.requireExperimentalFeature("flakes");
+        settings.requireExperimentalFeature(Xp::Flakes);
         command->second->prepare();
         command->second->run();
     }