libutil: return sources from runProgram2

this much more closely mimics what is actually happening: we're reading
data from somewhere else, actively, rather than passively waiting. with
the data flow matching the underlying system interactions better we can
remove a few sinkToSource calls that merely exists to undo the mismatch
caused by not treating subprocess output as a data source to begin with

Change-Id: If4abfc2f8398fb5e88c9b91a8bdefd5504bb2d11

1 files changed, 7 insertions, 3 deletions

diff --git a/src/libstore/build/derivation-goal.cc b/src/libstore/build/derivation-goal.cc
index a59984688..7c18f8b60 100644
--- a/src/libstore/build/derivation-goal.cc
+++ b/src/libstore/build/derivation-goal.cc
@@ -923,12 +923,16 @@ void runPostBuildHook(
     };
     LogSink sink(act);
 
-    runProgram2({
+    auto proc = runProgram2({
         .program = settings.postBuildHook,
         .environment = hookEnvironment,
-        .standardOut = &sink,
+        .captureStdout = true,
         .mergeStderrToStdout = true,
-    }).wait();
+    });
+    Finally const _wait([&] { proc.wait(); });
+
+    // FIXME just process the data, without a wrapper sink class
+    proc.stdout()->drainInto(sink);
 }
 
 void DerivationGoal::buildDone()