Store metadata about drv outputs realisations

For each known realisation, store:
- its output
- its output path

This comes with a set of needed changes:

- New `realisations` module declaring the types needed for describing
  these mappings
- New `Store::registerDrvOutput` method registering all the needed informations
  about a derivation output (also replaces `LocalStore::linkDeriverToPath`)
- new `Store::queryRealisation` method to retrieve the informations for a
  derivations

This introcudes some redundancy on the remote-store side between
`wopQueryDerivationOutputMap` and `wopQueryRealisation`.
However we might need to keep both (regardless of backwards compat)
because we sometimes need to get some infos for all the outputs of a
derivation (where `wopQueryDerivationOutputMap` is handy), but all the
stores can't implement it − because listing all the outputs of a
derivation isn't really possible for binary caches where the server
doesn't allow to list a directory.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/libstore/dummy-store.cc b/src/libstore/dummy-store.cc
index 98b745c3a..91fc178db 100644
--- a/src/libstore/dummy-store.cc
+++ b/src/libstore/dummy-store.cc
@@ -60,6 +60,9 @@ struct DummyStore : public Store, public virtual DummyStoreConfig
     BuildResult buildDerivation(const StorePath & drvPath, const BasicDerivation & drv,
         BuildMode buildMode) override
     { unsupported("buildDerivation"); }
+
+    std::optional<const Realisation> queryRealisation(const DrvOutput&) override
+    { unsupported("queryRealisation"); }
 };
 
 static RegisterStoreImplementation<DummyStore, DummyStoreConfig> regDummyStore;