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, 3 insertions, 1 deletions

diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 635a82a2a..0c8a4db56 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -10,8 +10,8 @@
 #include "sync.hh"
 #include "globals.hh"
 #include "config.hh"
-#include "derivations.hh"
 #include "path-info.hh"
+#include "repair-flag.hh"
 
 #include <atomic>
 #include <limits>
@@ -62,6 +62,8 @@ MakeError(BadStorePath, Error);
 
 MakeError(InvalidStoreURI, Error);
 
+struct BasicDerivation;
+struct Derivation;
 class FSAccessor;
 class NarInfoDiskCache;
 class Store;