Fix some warnings/bugs found by clang-tidy

src/libmain/progress-bar.cc

@@ -108,7 +108,8 @@ class ProgressBar : public Logger
         stop();
     }
 
-    void stop() override
+    /* Called by destructor, can't be overridden */
+    void stop() override final
     {
         {
             auto state(state_.lock());

src/libstore/build/local-derivation-goal.hh

@@ -272,8 +272,10 @@ struct LocalDerivationGoal : public DerivationGoal
 
     /**
      * Forcibly kill the child process, if any.
+     *
+     * Called by destructor, can't be overridden
      */
-    void killChild() override;
+    void killChild() override final;
 
     /**
      * Kill any processes running under the build user UID or in the

src/libstore/build/substitution-goal.hh

@@ -114,7 +114,8 @@ public:
     void handleChildOutput(int fd, std::string_view data) override;
     void handleEOF(int fd) override;
 
-    void cleanup() override;
+    /* Called by destructor, can't be overridden */
+    void cleanup() override final;
 
     JobCategory jobCategory() override { return JobCategory::Substitution; };
 };

src/libstore/filetransfer.cc

@@ -863,6 +863,8 @@ void FileTransfer::download(FileTransferRequest && request, Sink & sink)
             }
 
             chunk = std::move(state->data);
+            /* Reset state->data after the move, since we check data.empty() */
+            state->data = "";
 
             state->request.notify_one();
         }

src/libutil/args.cc

@@ -410,8 +410,8 @@ nlohmann::json MultiCommand::toJSON()
         auto cat = nlohmann::json::object();
         cat["id"] = command->category();
         cat["description"] = trim(categories[command->category()]);
-        j["category"] = std::move(cat);
         cat["experimental-feature"] = command->experimentalFeature();
+        j["category"] = std::move(cat);
         cmds[name] = std::move(j);
     }
 

src/libutil/logging.cc

@@ -67,7 +67,7 @@ class SimpleLogger : public Logger
             case lvlWarn: c = '4'; break;
             case lvlNotice: case lvlInfo: c = '5'; break;
             case lvlTalkative: case lvlChatty: c = '6'; break;
-            case lvlDebug: case lvlVomit: c = '7';
+            case lvlDebug: case lvlVomit: c = '7'; break;
             default: c = '7'; break; // should not happen, and missing enum case is reported by -Werror=switch-enum
             }
             prefix = std::string("<") + c + ">";