From ee97f107e8749d61ae5e310a2d457637ccc109ce Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Thu, 13 Apr 2023 13:38:12 -0400
Subject: [PATCH] Push `getFSAccessor` `unsupported(...)` down `Store` class
 hierarchy

More progress on issue #5729.

Instead of having it by the default method in `Store` itself, have it be
the implementation in `DummyStore` and `LegacySSHStore`. Then just the
implementations which fail to provide the method pay the "penalty" of
dealing with the icky `unimplemented` function for non-compliance.

Combined with my other recent PRs, this finally makes `Store` have no
`unsupported` calls!
---
 src/libstore/dummy-store.cc      | 3 +++
 src/libstore/legacy-ssh-store.cc | 3 +++
 src/libstore/store-api.hh        | 3 +--
 3 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/libstore/dummy-store.cc b/src/libstore/dummy-store.cc
index ae2777d0c..74d6ed3b5 100644
--- a/src/libstore/dummy-store.cc
+++ b/src/libstore/dummy-store.cc
@@ -71,6 +71,9 @@ struct DummyStore : public virtual DummyStoreConfig, public virtual Store
     void queryRealisationUncached(const DrvOutput &,
         Callback<std::shared_ptr<const Realisation>> callback) noexcept override
     { callback(nullptr); }
+
+    virtual ref<FSAccessor> getFSAccessor() override
+    { unsupported("getFSAccessor"); }
 };
 
 static RegisterStoreImplementation<DummyStore, DummyStoreConfig> regDummyStore;
diff --git a/src/libstore/legacy-ssh-store.cc b/src/libstore/legacy-ssh-store.cc
index eb471d8fc..d2ddbbe5f 100644
--- a/src/libstore/legacy-ssh-store.cc
+++ b/src/libstore/legacy-ssh-store.cc
@@ -342,6 +342,9 @@ public:
     void ensurePath(const StorePath & path) override
     { unsupported("ensurePath"); }
 
+    virtual ref<FSAccessor> getFSAccessor() override
+    { unsupported("getFSAccessor"); }
+
     void computeFSClosure(const StorePathSet & paths,
         StorePathSet & out, bool flipDirection = false,
         bool includeOutputs = false, bool includeDerivers = false) override
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 3cb48bff5..5bee272bf 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -678,8 +678,7 @@ public:
     /**
      * @return An object to access files in the Nix store.
      */
-    virtual ref<FSAccessor> getFSAccessor()
-    { unsupported("getFSAccessor"); }
+    virtual ref<FSAccessor> getFSAccessor() = 0;
 
     /**
      * Repair the contents of the given path by redownloading it using