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

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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 45a0ed82f0. That
commit in turn reverted 9ab07e99f5.
This commit is contained in:
John Ericson 2023-05-17 22:04:59 -04:00
parent 684e9be8b9
commit cb5052d98f
10 changed files with 182 additions and 151 deletions
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18
src/nix-store/nix-store.cc
View file

@ -849,7 +849,7 @@ static void opServe(Strings opFlags, Strings opArgs)
case cmdQueryValidPaths: {
bool lock = readInt(in);
bool substitute = readInt(in);
auto paths = worker_proto::read(*store, in, Phantom<StorePathSet> {});
auto paths = WorkerProto<StorePathSet>::read(*store, in);
if (lock && writeAllowed)
for (auto & path : paths)
store->addTempRoot(path);
@ -858,19 +858,19 @@ static void opServe(Strings opFlags, Strings opArgs)
store->substitutePaths(paths);
}
worker_proto::write(*store, out, store->queryValidPaths(paths));
workerProtoWrite(*store, out, store->queryValidPaths(paths));
break;
}
case cmdQueryPathInfos: {
auto paths = worker_proto::read(*store, in, Phantom<StorePathSet> {});
auto paths = WorkerProto<StorePathSet>::read(*store, in);
// !!! Maybe we want a queryPathInfos?
for (auto & i : paths) {
try {
auto info = store->queryPathInfo(i);
out << store->printStorePath(info->path)
<< (info->deriver ? store->printStorePath(*info->deriver) : "");
worker_proto::write(*store, out, info->references);
workerProtoWrite(*store, out, info->references);
// !!! Maybe we want compression?
out << info->narSize // downloadSize
<< info->narSize;
@ -898,7 +898,7 @@ static void opServe(Strings opFlags, Strings opArgs)
case cmdExportPaths: {
readInt(in); // obsolete
store->exportPaths(worker_proto::read(*store, in, Phantom<StorePathSet> {}), out);
store->exportPaths(WorkerProto<StorePathSet>::read(*store, in), out);
break;
}
@ -944,7 +944,7 @@ static void opServe(Strings opFlags, Strings opArgs)
DrvOutputs builtOutputs;
for (auto & [output, realisation] : status.builtOutputs)
builtOutputs.insert_or_assign(realisation.id, realisation);
worker_proto::write(*store, out, builtOutputs);
workerProtoWrite(*store, out, builtOutputs);
}
break;
@ -953,9 +953,9 @@ static void opServe(Strings opFlags, Strings opArgs)
case cmdQueryClosure: {
bool includeOutputs = readInt(in);
StorePathSet closure;
store->computeFSClosure(worker_proto::read(*store, in, Phantom<StorePathSet> {}),
store->computeFSClosure(WorkerProto<StorePathSet>::read(*store, in),
closure, false, includeOutputs);
worker_proto::write(*store, out, closure);
workerProtoWrite(*store, out, closure);
break;
}
@ -970,7 +970,7 @@ static void opServe(Strings opFlags, Strings opArgs)
};
if (deriver != "")
info.deriver = store->parseStorePath(deriver);
info.references = worker_proto::read(*store, in, Phantom<StorePathSet> {});
info.references = WorkerProto<StorePathSet>::read(*store, in);
in >> info.registrationTime >> info.narSize >> info.ultimate;
info.sigs = readStrings<StringSet>(in);
info.ca = ContentAddress::parseOpt(readString(in));