Revert "Revert "Use template structs instead of phantoms""

This is the more typically way to do [Argument-dependent
lookup](https://en.cppreference.com/w/cpp/language/adl)-leveraging
generic serializers in C++. It makes the relationship between the `read`
and `write` methods more clear and rigorous, and also looks more
familiar to users coming from other languages that do not have C++'s
libertine ad-hoc overloading.

I am returning to this because during the review in
https://github.com/NixOS/nix/pull/6223, it came up as something that
would make the code easier to read --- easier today hopefully already,
but definitely easier if we were have multiple codified protocols with
code sharing between them as that PR seeks to accomplish.

If I recall correctly, the main criticism of this the first time around
(in 2020) was that having to specify the type when writing, e.g.
`WorkerProto<MyType>::write`, was too verbose and cumbersome. This is
now addressed with the `workerProtoWrite` wrapper function.

This method is also the way `nlohmann::json`, which we have used for a
number of years now, does its serializers, for what its worth.

This reverts commit 45a0ed82f089158a79c8c25ef844c55e4a74fc35. That
commit in turn reverted 9ab07e99f527d1fa3adfa02839da477a1528d64b.

1 files changed, 8 insertions, 8 deletions

diff --git a/src/libstore/legacy-ssh-store.cc b/src/libstore/legacy-ssh-store.cc
index 2012584e0..9a470a99e 100644
--- a/src/libstore/legacy-ssh-store.cc
+++ b/src/libstore/legacy-ssh-store.cc
@@ -146,7 +146,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
             auto deriver = readString(conn->from);
             if (deriver != "")
                 info->deriver = parseStorePath(deriver);
-            info->references = worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});
+            info->references = WorkerProto<StorePathSet>::read(*this, conn->from);
             readLongLong(conn->from); // download size
             info->narSize = readLongLong(conn->from);
 
@@ -180,7 +180,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
                 << printStorePath(info.path)
                 << (info.deriver ? printStorePath(*info.deriver) : "")
                 << info.narHash.to_string(Base16, false);
-            worker_proto::write(*this, conn->to, info.references);
+            workerProtoWrite(*this, conn->to, info.references);
             conn->to
                 << info.registrationTime
                 << info.narSize
@@ -209,7 +209,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
             conn->to
                 << exportMagic
                 << printStorePath(info.path);
-            worker_proto::write(*this, conn->to, info.references);
+            workerProtoWrite(*this, conn->to, info.references);
             conn->to
                 << (info.deriver ? printStorePath(*info.deriver) : "")
                 << 0
@@ -294,7 +294,7 @@ public:
         if (GET_PROTOCOL_MINOR(conn->remoteVersion) >= 3)
             conn->from >> status.timesBuilt >> status.isNonDeterministic >> status.startTime >> status.stopTime;
         if (GET_PROTOCOL_MINOR(conn->remoteVersion) >= 6) {
-            auto builtOutputs = worker_proto::read(*this, conn->from, Phantom<DrvOutputs> {});
+            auto builtOutputs = WorkerProto<DrvOutputs>::read(*this, conn->from);
             for (auto && [output, realisation] : builtOutputs)
                 status.builtOutputs.insert_or_assign(
                     std::move(output.outputName),
@@ -358,10 +358,10 @@ public:
         conn->to
             << cmdQueryClosure
             << includeOutputs;
-        worker_proto::write(*this, conn->to, paths);
+        workerProtoWrite(*this, conn->to, paths);
         conn->to.flush();
 
-        for (auto & i : worker_proto::read(*this, conn->from, Phantom<StorePathSet> {}))
+        for (auto & i : WorkerProto<StorePathSet>::read(*this, conn->from))
             out.insert(i);
     }
 
@@ -374,10 +374,10 @@ public:
             << cmdQueryValidPaths
             << false // lock
             << maybeSubstitute;
-        worker_proto::write(*this, conn->to, paths);
+        workerProtoWrite(*this, conn->to, paths);
         conn->to.flush();
 
-        return worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});
+        return WorkerProto<StorePathSet>::read(*this, conn->from);
     }
 
     void connect() override