Allow activities to be nested

In particular, this allows more relevant activities ("substituting X")
to supersede inferior ones ("downloading X").

src/libstore/build.cc

@@ -2407,14 +2407,14 @@ struct BuilderLogger : Logger
     }
 
     void startActivity(ActivityId act, ActivityType type,
-        const std::string & s, const Fields & fields) override
+        const std::string & s, const Fields & fields, ActivityId parent) override
     {
         nlohmann::json json;
         json["action"] = "start";
         json["id"] = act;
         json["type"] = type;
         json["text"] = s;
-        // FIXME: handle fields
+        // FIXME: handle fields, parent
         log(lvlError, "@nix " + json.dump());
     }
 
@@ -3313,7 +3313,7 @@ void DerivationGoal::flushLine()
                 if (type == actDownload)
                     builderActivities.emplace(std::piecewise_construct,
                         std::forward_as_tuple(json["id"]),
-                        std::forward_as_tuple(*logger, type, json["text"]));
+                        std::forward_as_tuple(*logger, type, json["text"], Logger::Fields{}, act->id));
             }
 
             else if (action == "stop")
@@ -3655,6 +3655,9 @@ void SubstitutionGoal::tryToRun()
             /* Wake up the worker loop when we're done. */
             Finally updateStats([this]() { outPipe.writeSide = -1; });
 
+            Activity act(*logger, actSubstitute, "", Logger::Fields{storePath, sub->getUri()});
+            PushActivity pact(act.id);
+
             copyStorePath(ref<Store>(sub), ref<Store>(worker.store.shared_from_this()),
                 storePath, repair);
 

src/libstore/download.cc

@@ -85,7 +85,7 @@ struct CurlDownloader : public Downloader
         DownloadItem(CurlDownloader & downloader, const DownloadRequest & request)
             : downloader(downloader)
             , request(request)
-            , act(*logger, actDownload, fmt("downloading '%s'", request.uri))
+            , act(*logger, actDownload, fmt("downloading '%s'", request.uri), {}, request.parentAct)
         {
             if (!request.expectedETag.empty())
                 requestHeaders = curl_slist_append(requestHeaders, ("If-None-Match: " + request.expectedETag).c_str());

src/libstore/download.hh

@@ -16,8 +16,10 @@ struct DownloadRequest
     bool head = false;
     size_t tries = 5;
     unsigned int baseRetryTimeMs = 250;
+    ActivityId parentAct;
 
-    DownloadRequest(const std::string & uri) : uri(uri) { }
+    DownloadRequest(const std::string & uri)
+        : uri(uri), parentAct(curActivity) { }
 };
 
 struct DownloadResult

src/libstore/store-api.cc

@@ -565,7 +565,9 @@ void Store::buildPaths(const PathSet & paths, BuildMode buildMode)
 void copyStorePath(ref<Store> srcStore, ref<Store> dstStore,
     const Path & storePath, RepairFlag repair, CheckSigsFlag checkSigs)
 {
-    Activity act(*logger, actCopyPath, fmt("copying path '%s'", storePath));
+    Activity act(*logger, actCopyPath, fmt("copying path '%s'", storePath),
+        {storePath, srcStore->getUri(), dstStore->getUri()});
+    PushActivity pact(act.id);
 
     auto info = srcStore->queryPathInfo(storePath);
 

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);
 }
 
 }

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();

src/nix/progress-bar.cc

@@ -73,6 +73,8 @@ private:
         uint64_t running = 0;
         uint64_t failed = 0;
         std::map<ActivityType, uint64_t> expectedByType;
+        bool visible = true;
+        ActivityId parent;
     };
 
     struct ActivitiesByType
@@ -125,7 +127,7 @@ public:
     }
 
     void startActivity(ActivityId act, ActivityType type, const std::string & s,
-        const Fields & fields) override
+        const Fields & fields, ActivityId parent) override
     {
         auto state(state_.lock());
 
@@ -133,6 +135,7 @@ public:
         auto i = std::prev(state->activities.end());
         i->s = s;
         i->type = type;
+        i->parent = parent;
         state->its.emplace(act, i);
         state->activitiesByType[type].its.emplace(act, i);
 
@@ -143,9 +146,30 @@ public:
             i->s = fmt("building " ANSI_BOLD "%s" ANSI_NORMAL, name);
         }
 
+        if (type == actSubstitute) {
+            auto name = storePathToName(getS(fields, 0));
+            i->s = fmt("fetching " ANSI_BOLD "%s" ANSI_NORMAL " from %s", name, getS(fields, 1));
+        }
+
+        if ((type == actDownload && hasAncestor(*state, actCopyPath, parent))
+            || (type == actCopyPath && hasAncestor(*state, actSubstitute, parent)))
+            i->visible = false;
+
         update(*state);
     }
 
+    /* Check whether an activity has an ancestore with the specified
+       type. */
+    bool hasAncestor(State & state, ActivityType type, ActivityId act)
+    {
+        while (act != 0) {
+            auto i = state.its.find(act);
+            if (i == state.its.end()) break;
+            if (i->second->type == type) return true;
+        }
+        return false;
+    }
+
     void stopActivity(ActivityId act) override
     {
         auto state(state_.lock());
@@ -253,7 +277,7 @@ public:
             if (!status.empty()) line += " ";
             auto i = state.activities.rbegin();
 
-            while (i != state.activities.rend() && i->s.empty() && i->s2.empty())
+            while (i != state.activities.rend() && (!i->visible || (i->s.empty() && i->s2.empty())))
                 ++i;
 
             if (i != state.activities.rend()) {