Separate store configs from the implems

Rework the `Store` hierarchy so that there's now one hierarchy for the
store configs and one for the implementations (where each implementation
extends the corresponding config). So a class hierarchy like

```
StoreConfig-------->Store
    |                 |
    v                 v
SubStoreConfig----->SubStore
    |                 |
    v                 v
SubSubStoreConfig-->SubSubStore
```

(with virtual inheritance to prevent DDD).

The advantage of this architecture is that we can now introspect the configuration of a store without having to instantiate the store itself

1 files changed, 3 insertions, 1 deletions

diff --git a/src/libstore/dummy-store.cc b/src/libstore/dummy-store.cc
index 52086445e..d4560c13d 100644
--- a/src/libstore/dummy-store.cc
+++ b/src/libstore/dummy-store.cc
@@ -2,6 +2,8 @@
 
 namespace nix {
 
+struct DummyStoreConfig : StoreConfig {};
+
 struct DummyStore : public Store
 {
     DummyStore(const std::string uri, const Params & params)
@@ -54,6 +56,6 @@ struct DummyStore : public Store
     { unsupported("buildDerivation"); }
 };
 
-static RegisterStoreImplementation<DummyStore> regStore;
+static RegisterStoreImplementation<DummyStore, DummyStoreConfig> regStore;
 
 }