2 files changed, 16 insertions, 4 deletions
diff --git a/src/libutil/logging.cc b/src/libutil/logging.cc
index 87f20664ef08..b103b902eab0 100644
--- a/src/libutil/logging.cc
+++ b/src/libutil/logging.cc
@@ -5,6 +5,8 @@
 
 namespace nix {
 
+thread_local ActivityId curActivity = 0;
+
 Logger * logger = makeDefaultLogger();
 
 void Logger::warn(const std::string & msg)
@@ -75,10 +77,10 @@ Logger * makeDefaultLogger()
 std::atomic<uint64_t> nextId{(uint64_t) getpid() << 32};
 
 Activity::Activity(Logger & logger, ActivityType type,
-    const std::string & s, const Logger::Fields & fields)
+    const std::string & s, const Logger::Fields & fields, ActivityId parent)
     : logger(logger), id(nextId++)
 {
-    logger.startActivity(id, type, s, fields);
+    logger.startActivity(id, type, s, fields, parent);
 }
 
 }
diff --git a/src/libutil/logging.hh b/src/libutil/logging.hh
index 567af361e8e9..9427f268267a 100644
--- a/src/libutil/logging.hh
+++ b/src/libutil/logging.hh
@@ -23,6 +23,7 @@ typedef enum {
     actBuild = 105,
     actOptimiseStore = 106,
     actVerifyPaths = 107,
+    actSubstitute = 108,
 } ActivityType;
 
 typedef enum {
@@ -65,7 +66,7 @@ public:
     virtual void warn(const std::string & msg);
 
     virtual void startActivity(ActivityId act, ActivityType type,
-        const std::string & s, const Fields & fields) { };
+        const std::string & s, const Fields & fields, ActivityId parent) { };
 
     virtual void stopActivity(ActivityId act) { };
 
@@ -76,6 +77,8 @@ public:
     virtual void result(ActivityId act, ResultType type, const Fields & fields) { };
 };
 
+extern thread_local ActivityId curActivity;
+
 struct Activity
 {
     Logger & logger;
@@ -83,7 +86,7 @@ struct Activity
     const ActivityId id;
 
     Activity(Logger & logger, ActivityType type, const std::string & s = "",
-        const Logger::Fields & fields = {});
+        const Logger::Fields & fields = {}, ActivityId parent = curActivity);
 
     Activity(const Activity & act) = delete;
 
@@ -107,6 +110,13 @@ struct Activity
     friend class Logger;
 };
 
+struct PushActivity
+{
+    const ActivityId prevAct;
+    PushActivity(ActivityId act) : prevAct(curActivity) { curActivity = act; }
+    ~PushActivity() { curActivity = prevAct; }
+};
+
 extern Logger * logger;
 
 Logger * makeDefaultLogger();