Improved logging abstraction

This also gets rid of --log-type, since the nested log type isn't
useful in a multi-threaded situation, and nobody cares about the
"pretty" log type.

src/nix/progress-bar.hh

@@ -1,49 +1,15 @@
 #pragma once
 
-#include "sync.hh"
-#include "util.hh"
+#include "logging.hh"
 
 namespace nix {
 
-class ProgressBar
+class StartProgressBar
 {
-private:
-    struct State
-    {
-        std::string status;
-        bool done = false;
-        std::list<std::string> activities;
-    };
-
-    Sync<State> state;
-
+    Logger * prev = 0;
 public:
-
-    ProgressBar();
-
-    ~ProgressBar();
-
-    void updateStatus(const std::string & s);
-
-    void done();
-
-    class Activity
-    {
-        friend class ProgressBar;
-    private:
-        ProgressBar & pb;
-        std::list<std::string>::iterator it;
-        Activity(ProgressBar & pb, const FormatOrString & fs);
-    public:
-        ~Activity();
-    };
-
-    Activity startActivity(const FormatOrString & fs);
-
-private:
-
-    void render(State & state_);
-
+    StartProgressBar();
+    ~StartProgressBar();
 };
 
 }