feat(tvix): Introduce build event streams in worker protocol

Introduces a new `BuildEvent` proto type which is streamed in response
to calls that trigger builds of derivations.

This type can currently supply build statuses, log lines and
information about builds starting.

This is in preparation for threading build logs through the processes.

Since we have nowhere to send the logs (yet), a null sink is used
instead.

Co-authored-by: Griffin Smith <grfn@gws.fyi>
Change-Id: If7332337b89506c7e404cd20174acdaa1a3be4e8
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1793
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>
Reviewed-by: kanepyork <rikingcoding@gmail.com>

third_party/nix/src/libstore/rpc-store.cc

@@ -3,6 +3,7 @@
 #include <algorithm>
 #include <filesystem>
 #include <memory>
+#include <optional>
 
 #include <absl/status/status.h>
 #include <absl/strings/str_cat.h>
@@ -326,8 +327,32 @@ absl::Status RpcStore::buildPaths(const PathSet& paths, BuildMode buildMode) {
 
   google::protobuf::Empty response;
   request.set_mode(nix::BuildModeToProto(buildMode));
-  return nix::util::proto::GRPCStatusToAbsl(
-      stub_->BuildPaths(&ctx, request, &response));
+
+  // TODO(tazjin): Temporary no-op sink used to discard build output,
+  // but satisfy the compiler. A real one is needed.
+  //
+  // Maybe this should just be stderr, considering that this is the
+  // *client*, but I'm not sure.
+  std::ostream discard_logs = DiscardLogsSink();
+
+  std::unique_ptr<grpc::ClientReader<proto::BuildEvent>> reader =
+      stub_->BuildPaths(&ctx, request);
+
+  proto::BuildEvent event;
+  while (reader->Read(&event)) {
+    if (event.has_build_log()) {
+      // TODO(tazjin): Include .path()?
+      discard_logs << event.build_log().line();
+    } else {
+      discard_logs << std::endl
+                   << "Building path: " << event.building_path().path()
+                   << std::endl;
+    }
+
+    // has_result() is not in use in this call (for now)
+  }
+
+  return nix::util::proto::GRPCStatusToAbsl(reader->Finish());
 }
 
 BuildResult RpcStore::buildDerivation(const Path& drvPath,
@@ -339,11 +364,25 @@ BuildResult RpcStore::buildDerivation(const Path& drvPath,
   auto proto_drv = drv.to_proto();
   request.set_allocated_derivation(&proto_drv);
   request.set_build_mode(BuildModeToProto(buildMode));
-  proto::BuildDerivationResponse response;
-  SuccessOrThrow(stub_->BuildDerivation(&ctx, request, &response),
-                 __FUNCTION__);
 
-  const auto result = BuildResult::FromProto(response);
+  // Same note as in ::buildPaths ...
+  std::ostream discard_logs = DiscardLogsSink();
+
+  std::unique_ptr<grpc::ClientReader<proto::BuildEvent>> reader =
+      stub_->BuildDerivation(&ctx, request);
+
+  std::optional<BuildResult> result;
+
+  proto::BuildEvent event;
+  while (reader->Read(&event)) {
+    if (event.has_build_log()) {
+      discard_logs << event.build_log().line();
+    } else if (event.has_result()) {
+      result = BuildResult::FromProto(event.result());
+    }
+  }
+  SuccessOrThrow(reader->Finish(), __FUNCTION__);
+
   if (!result.has_value()) {
     throw Error("Invalid response from daemon for buildDerivation");
   }

third_party/nix/src/libstore/store-api.cc

@@ -92,7 +92,7 @@ nix::proto::BuildStatus BuildResult::status_to_proto() {
 }
 
 std::optional<BuildResult> BuildResult::FromProto(
-    const nix::proto::BuildDerivationResponse& resp) {
+    const nix::proto::BuildResult& resp) {
   BuildResult result;
   switch (resp.status()) {
     case proto::BuildStatus::Built:
@@ -125,7 +125,7 @@ std::optional<BuildResult> BuildResult::FromProto(
       return {};
   }
 
-  result.errorMsg = resp.error_message();
+  result.errorMsg = resp.msg();
   return result;
 }
 

third_party/nix/src/libstore/store-api.hh

@@ -189,7 +189,7 @@ struct ValidPathInfo {
   virtual ~ValidPathInfo() {}
 };
 
-typedef std::list<ValidPathInfo> ValidPathInfos;
+using ValidPathInfos = std::list<ValidPathInfo>;
 
 enum BuildMode { bmNormal, bmRepair, bmCheck };
 
@@ -243,7 +243,7 @@ struct BuildResult {
   nix::proto::BuildStatus status_to_proto();
 
   static std::optional<BuildResult> FromProto(
-      const nix::proto::BuildDerivationResponse& resp);
+      const nix::proto::BuildResult& resp);
 };
 
 class Store : public std::enable_shared_from_this<Store>, public Config {