[libcalamares] Make setup of log-level explicit

- Replace the implicit setting of a logging level
   (the first time logging is called) with explicit
   setupLogLevel().

src/libcalamares/utils/Logger.cpp

@@ -35,31 +35,28 @@
 #define LOGFILE_SIZE 1024 * 256
 
 static std::ofstream logfile;
-static unsigned int s_threshold = 0;  // Set to non-zero on first logging call
+static unsigned int s_threshold =
+#ifdef QT_NO_DEBUG
+            Logger::LOG_DISABLE;
+#else
+            Logger::LOGEXTRA + 1;  // Comparison is < in log() function
+#endif
 static QMutex s_mutex;
 
 namespace Logger
 {
 
+void
+setupLogLevel(unsigned int level)
+{
+    if ( level > LOGVERBOSE )
+        level = LOGVERBOSE;
+    s_threshold = level + 1;  // Comparison is < in log() function
+}
+
 static void
 log( const char* msg, unsigned int debugLevel, bool toDisk = true )
 {
-    if ( !s_threshold )
-    {
-        if ( qApp->arguments().contains( "--debug" ) ||
-             qApp->arguments().contains( "-d" ) ||
-             qApp->arguments().contains( "-D" ) )
-            s_threshold = LOGVERBOSE;
-        else
-#ifdef QT_NO_DEBUG
-            s_threshold = LOG_DISABLE;
-#else
-            s_threshold = LOGEXTRA;
-#endif
-        // Comparison is < threshold, below
-        ++s_threshold;
-    }
-
     if ( toDisk || debugLevel < s_threshold )
     {
         QMutexLocker lock( &s_mutex );

src/libcalamares/utils/Logger.h

@@ -61,6 +61,17 @@ namespace Logger
     DLLEXPORT void CalamaresLogHandler( QtMsgType type, const QMessageLogContext& context, const QString& msg );
     DLLEXPORT void setupLogfile();
     DLLEXPORT QString logFile();
+
+    /**
+     * @brief Set a log level for future logging.
+     *
+     * Pass in a value from the LOG* enum, above. Use 0 to
+     * disable logging. Values greater than LOGVERBOSE are
+     * limited to LOGVERBOSE, which will log everything.
+     *
+     * Practical values are 0, 1, 2, and 6.
+     */
+    DLLEXPORT void setupLogLevel( unsigned int level );
 }
 
 #define cLog Logger::CLog