fix: recent FTBFS in msvc (#2907)

* fix: recent FTBFS in msvc

It's happening a line in qt/WatchDir.cc where an enum named `ERROR` is
declared, so it's probably conflicting with a new `ERROR` name in some
header file. Rename ours and make at an `enum class` for good measure.

* build: fix cmake msvc warning

D9025 : overriding /W3 with /W4

CMakeLists.txt

@@ -1,5 +1,9 @@
 cmake_minimum_required(VERSION 3.9 FATAL_ERROR)
 
+if(POLICY CMP0092)
+    cmake_policy(SET CMP0092 NEW)
+endif()
+
 # The value of this variable should be set prior to the first project() command invocation.
 # See: https://cmake.org/cmake/help/latest/variable/CMAKE_OSX_DEPLOYMENT_TARGET.html
 if(CMAKE_OSX_DEPLOYMENT_TARGET STREQUAL "")

qt/WatchDir.cc

@@ -30,27 +30,27 @@ WatchDir::WatchDir(TorrentModel const& model)
 ****
 ***/
 
-int WatchDir::metainfoTest(QString const& filename) const
+WatchDir::AddResult WatchDir::metainfoTest(QString const& filename) const
 {
     auto metainfo = tr_torrent_metainfo();
     if (!metainfo.parseTorrentFile(filename.toUtf8().constData()))
     {
-        return ERROR;
+        return AddResult::Error;
     }
 
     if (model_.hasTorrent(TorrentHash{ metainfo.infoHash() }))
     {
-        return DUPLICATE;
+        return AddResult::Duplicate;
     }
 
-    return OK;
+    return AddResult::Success;
 }
 
 void WatchDir::onTimeout()
 {
     auto* t = qobject_cast<QTimer*>(sender());
 
-    if (auto const filename = t->objectName(); metainfoTest(filename) == OK)
+    if (auto const filename = t->objectName(); metainfoTest(filename) == AddResult::Success)
     {
         emit torrentFileAdded(filename);
     }
@@ -98,14 +98,14 @@ void WatchDir::watcherActivated(QString const& path)
 
             switch (metainfoTest(filename))
             {
-            case OK:
+            case AddResult::Success:
                 emit torrentFileAdded(filename);
                 break;
 
-            case DUPLICATE:
+            case AddResult::Duplicate:
                 break;
 
-            case ERROR:
+            case AddResult::Error:
                 {
                     // give the torrent a few seconds to finish downloading
                     auto* t = new QTimer(this);

qt/WatchDir.h

@@ -36,14 +36,14 @@ private slots:
     void rescanAllWatchedDirectories();
 
 private:
-    enum
+    enum class AddResult
     {
-        OK,
-        DUPLICATE,
-        ERROR
+        Success,
+        Duplicate,
+        Error
     };
 
-    int metainfoTest(QString const& filename) const;
+    AddResult metainfoTest(QString const& filename) const;
 
     TorrentModel const& model_;