nix copy: Revive progress bar

src/libutil/archive.cc

@@ -56,6 +56,8 @@ static void dumpContents(const Path & path, size_t size,
 
 static void dump(const Path & path, Sink & sink, PathFilter & filter)
 {
+    checkInterrupt();
+
     struct stat st;
     if (lstat(path.c_str(), &st))
         throw SysError(format("getting attributes of path '%1%'") % path);

src/libutil/logging.cc

@@ -80,4 +80,15 @@ std::atomic<uint64_t> nextId{(uint64_t) getpid() << 32};
 
 Activity::Activity() : id(nextId++) { };
 
+Activity::Activity(ActivityType type, std::string msg)
+    : Activity()
+{
+    logger->event(evStartActivity, id, msg);
+}
+
+Activity::~Activity()
+{
+    logger->event(evStopActivity, id);
+}
+
 }

src/libutil/logging.hh

@@ -13,6 +13,10 @@ typedef enum {
     lvlVomit
 } Verbosity;
 
+typedef enum {
+    actCopyPath = 100,
+} ActivityType;
+
 class Activity
 {
 public:
@@ -21,6 +25,10 @@ public:
     Activity();
     Activity(const Activity & act) : id(act.id) { };
     Activity(uint64_t id) : id(id) { };
+    Activity(ActivityType type, std::string msg = "");
+    ~Activity();
+
+    //void progress(...);
 };
 
 typedef enum {
@@ -35,6 +43,13 @@ typedef enum {
     evSubstitutionCreated = 8,
     evSubstitutionStarted = 9,
     evSubstitutionFinished = 10,
+
+    evCopyStarted = 100,
+    evCopyProgress = 101,
+
+    evStartActivity = 1000,
+    evStopActivity = 1001,
+
 } EventType;
 
 struct Event