Clean up `DerivationOutput`, and headers

1. `DerivationOutput` now as the `std::variant` as a base class. And the
   variants are given hierarchical names under `DerivationOutput`.

   In 8e0d0689be797f9e42f9b43b06f50c1af7f20b4a @matthewbauer and I
   didn't know a better idiom, and so we made it a field. But this sort
   of "newtype" is anoying for literals downstream.

   Since then we leaned the base class, inherit the constructors trick,
   e.g. used in `DerivedPath`. Switching to use that makes this more
   ergonomic, and consistent.

2. `store-api.hh` and `derivations.hh` are now independent.

   In bcde5456cc3295061a0726881c3e441444dd6680 I swapped the dependency,
   but I now know it is better to just keep on using incomplete types as
   much as possible for faster compilation and good separation of
   concerns.

1 files changed, 7 insertions, 5 deletions

diff --git a/src/nix/develop.cc b/src/nix/develop.cc
index dafcafd79..6baf539c3 100644
--- a/src/nix/develop.cc
+++ b/src/nix/develop.cc
@@ -196,14 +196,14 @@ static StorePath getDerivationEnvironment(ref<Store> store, ref<Store> evalStore
     drv.inputSrcs.insert(std::move(getEnvShPath));
     if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations)) {
         for (auto & output : drv.outputs) {
-            output.second = {
-                .output = DerivationOutputDeferred{},
-            };
+            output.second = DerivationOutput::Deferred {},
             drv.env[output.first] = hashPlaceholder(output.first);
         }
     } else {
         for (auto & output : drv.outputs) {
-            output.second = { .output = DerivationOutputInputAddressed { .path = StorePath::dummy } };
+            output.second = DerivationOutput::InputAddressed {
+                .path = StorePath::dummy,
+            };
             drv.env[output.first] = "";
         }
         auto h0 = hashDerivationModulo(*evalStore, drv, true);
@@ -211,7 +211,9 @@ static StorePath getDerivationEnvironment(ref<Store> store, ref<Store> evalStore
 
         for (auto & output : drv.outputs) {
             auto outPath = store->makeOutputPath(output.first, h, drv.name);
-            output.second = { .output = DerivationOutputInputAddressed { .path = outPath } };
+            output.second = DerivationOutput::InputAddressed {
+                .path = outPath,
+            };
             drv.env[output.first] = store->printStorePath(outPath);
         }
     }