Isolate the default cache directory

Instead of having it in several random places, have a central function
that contains all the cache directory selection logic.

As per QtCore docs GenericCacheLocation can be empty so introduce a fallback
to CacheLocation (the app-specific, non-shared location) in case some
future platform does not support the former.

Task-number: QTBUG-41187
Change-Id: Icfe5e8926e917483ac11844f625244318ff815c7
Reviewed-by: Alex Blasche <alexander.blasche@theqtcompany.com>

6 files changed, 38 insertions, 15 deletions

diff --git a/src/location/doc/src/plugins/nokia.qdoc b/src/location/doc/src/plugins/nokia.qdoc
index f1a6828a..1ed5e6e1 100644
--- a/src/location/doc/src/plugins/nokia.qdoc
+++ b/src/location/doc/src/plugins/nokia.qdoc
@@ -92,7 +92,9 @@ a prefix.
     \li here.mapping.cache.directory
     \li Absolute path to map tile cache directory used as network disk cache.
 
-    Default place for the cache is "QtLocation" directory in \l {QStandardPaths::writableLocation()} {QStandardPaths::writableLocation}(\l{QStandardPaths::GenericCacheLocation}).
+    The default place for the cache is \c{QtLocation/here} directory in \l {QStandardPaths::writableLocation()} {QStandardPaths::writableLocation}(\l{QStandardPaths::GenericCacheLocation}).
+    On systems that have no concept of a shared cache, the application-specific \l{QStandardPaths::CacheLocation} is used instead.
+
 \row
     \li here.mapping.cache.disk.size
     \li Map tile disk cache size in bytes. Default size of the cache is 20MB.
diff --git a/src/location/doc/src/plugins/osm.qdoc b/src/location/doc/src/plugins/osm.qdoc
index f6de9c20..1c924fd3 100644
--- a/src/location/doc/src/plugins/osm.qdoc
+++ b/src/location/doc/src/plugins/osm.qdoc
@@ -106,4 +106,12 @@ Plugin {
     PluginParameter { name: "osm.geocoding.host"; value: "http://geocoding.server.address" }
 }
 \endcode
+
+\section1 Other Plugin-specific Information
+
+\section2 Tile cache
+
+The tiles are cached in a \c{QtLocation/osm} directory in \l {QStandardPaths::writableLocation()}{QStandardPaths::writableLocation}
+(\l{QStandardPaths::GenericCacheLocation}). On systems that have no concept of a shared cache, the application-specific
+\l{QStandardPaths::CacheLocation} is used instead.
 */
diff --git a/src/location/maps/qgeotilecache.cpp b/src/location/maps/qgeotilecache.cpp
index 4e15504d..3da2865b 100644
--- a/src/location/maps/qgeotilecache.cpp
+++ b/src/location/maps/qgeotilecache.cpp
@@ -100,14 +100,10 @@ QGeoTileCache::QGeoTileCache(const QString &directory, QObject *parent)
     qRegisterMetaType<QList<QGeoTileSpec> >();
     qRegisterMetaType<QSet<QGeoTileSpec> >();
 
-    // We keep default values here so that they are in one place
-    // rather than in each individual plugin (the plugins can
-    // of course override them)
-
-    const QString basePath = QStandardPaths::writableLocation(QStandardPaths::GenericCacheLocation)
-                 + QLatin1String("/QtLocation");
+    const QString basePath = baseCacheDirectory();
 
     // delete old tiles from QtLocation 5.4 or prior
+    // Newer version use plugin-specific subdirectories so those are not affected.
     // TODO Remove cache cleanup in Qt 6
     QDir baseDir(basePath);
     if (baseDir.exists()) {
@@ -118,8 +114,7 @@ QGeoTileCache::QGeoTileCache(const QString &directory, QObject *parent)
 
     if (directory_.isEmpty()) {
         directory_ = basePath;
-        qWarning() << "Plugin uses uninitialized directory for QGeoTileCache"
-                      " which will was deleted during startup";
+        qWarning() << "Plugin uses uninitialized QGeoTileCache directory which was deleted during startup";
     }
 
     QDir::root().mkpath(directory_);
@@ -465,4 +460,23 @@ QGeoTileSpec QGeoTileCache::filenameToTileSpec(const QString &filename)
                     numbers.at(4));
 }
 
+QString QGeoTileCache::baseCacheDirectory()
+{
+    QString dir;
+
+    // Try the shared cache first and use a specific directory. (e.g. ~/.cache/QtLocation)
+    // If this is not supported by the platform, use the application-specific cache
+    // location. (e.g. ~/.cache/<app_name>/QtLocation)
+    dir = QStandardPaths::writableLocation(QStandardPaths::GenericCacheLocation);
+    if (dir.isEmpty())
+        dir = QStandardPaths::writableLocation(QStandardPaths::CacheLocation);
+
+    if (!dir.endsWith(QLatin1Char('/')))
+        dir += QLatin1Char('/');
+
+    dir += QLatin1String("QtLocation/");
+
+    return dir;
+}
+
 QT_END_NAMESPACE
diff --git a/src/location/maps/qgeotilecache_p.h b/src/location/maps/qgeotilecache_p.h
index 9cf31db0..d9f7bce9 100644
--- a/src/location/maps/qgeotilecache_p.h
+++ b/src/location/maps/qgeotilecache_p.h
@@ -141,6 +141,8 @@ public:
                 QGeoTiledMappingManagerEngine::CacheAreas areas = QGeoTiledMappingManagerEngine::AllCaches);
     void handleError(const QGeoTileSpec &spec, const QString &errorString);
 
+    static QString baseCacheDirectory();
+
 public Q_SLOTS:
     void printStats();
 
diff --git a/src/location/maps/qgeotiledmappingmanagerengine.cpp b/src/location/maps/qgeotiledmappingmanagerengine.cpp
index b9322c13..43f56872 100644
--- a/src/location/maps/qgeotiledmappingmanagerengine.cpp
+++ b/src/location/maps/qgeotiledmappingmanagerengine.cpp
@@ -288,10 +288,8 @@ QGeoTileCache *QGeoTiledMappingManagerEngine::tileCache()
     Q_D(QGeoTiledMappingManagerEngine);
     if (!d->tileCache_) {
         QString cacheDirectory;
-        if (!managerName().isEmpty()) {
-            cacheDirectory = QStandardPaths::writableLocation(QStandardPaths::GenericCacheLocation)
-                    + QLatin1String("/QtLocation/") + managerName();
-        }
+        if (!managerName().isEmpty())
+            cacheDirectory = QGeoTileCache::baseCacheDirectory() + managerName();
         d->tileCache_ = new QGeoTileCache(cacheDirectory);
     }
     return d->tileCache_;
diff --git a/src/plugins/geoservices/nokia/qgeotiledmappingmanagerengine_nokia.cpp b/src/plugins/geoservices/nokia/qgeotiledmappingmanagerengine_nokia.cpp
index 54bf29af..1b1163a6 100644
--- a/src/plugins/geoservices/nokia/qgeotiledmappingmanagerengine_nokia.cpp
+++ b/src/plugins/geoservices/nokia/qgeotiledmappingmanagerengine_nokia.cpp
@@ -106,8 +106,7 @@ QGeoTiledMappingManagerEngineNokia::QGeoTiledMappingManagerEngineNokia(
         cacheDir = parameters.value(QStringLiteral("here.mapping.cache.directory")).toString();
     } else {
         // managerName() is not yet set, we have to hardcode the plugin name below
-        cacheDir = QStandardPaths::writableLocation(QStandardPaths::GenericCacheLocation)
-                + QLatin1String("/QtLocation/here");
+        cacheDir = QGeoTileCache::baseCacheDirectory() + QLatin1String("here");
     }
 
     QGeoTileCache *tileCache = createTileCacheWithDir(cacheDir);