libstore: clarify that build log fd and hook log fd are different

only DerivationGoal can set the hook to anything at all. it always sets
buildOutFD to something that is not related to fromHook in any way, and
mixing the two would have rather dire consequences for log consistency.

Change-Id: Ida86727fd1cd5e1ecd78f07f3bde330a346658a8

1 files changed, 3 insertions, 4 deletions

diff --git a/src/libstore/build/derivation-goal.cc b/src/libstore/build/derivation-goal.cc
index f43a2a5b6..cc445a0a4 100644
--- a/src/libstore/build/derivation-goal.cc
+++ b/src/libstore/build/derivation-goal.cc
@@ -1288,9 +1288,7 @@ Goal::WorkResult DerivationGoal::handleChildOutput(int fd, std::string_view data
     };
 
     // local & `ssh://`-builds are dealt with here.
-    auto isWrittenToLog = fd == builderOutFD->get();
-    if (isWrittenToLog)
-    {
+    if (fd == builderOutFD->get()) {
         logSize += data.size();
         if (settings.maxLogSize && logSize > settings.maxLogSize) {
             return tooMuchLogs();
@@ -1308,6 +1306,7 @@ Goal::WorkResult DerivationGoal::handleChildOutput(int fd, std::string_view data
             }
 
         if (logSink) (*logSink)(data);
+        return StillAlive{};
     }
 
     if (hook && fd == hook->fromHook.readSide.get()) {
@@ -1318,7 +1317,7 @@ Goal::WorkResult DerivationGoal::handleChildOutput(int fd, std::string_view data
                     auto s = handleJSONLogMessage(*json, worker.act, hook->activities, true);
                     // ensure that logs from a builder using `ssh-ng://` as protocol
                     // are also available to `nix log`.
-                    if (s && !isWrittenToLog && logSink) {
+                    if (s && logSink) {
                         const auto type = (*json)["type"];
                         const auto fields = (*json)["fields"];
                         if (type == resBuildLogLine) {