WINDOWS: Don't create keys in the registry if python isn't found. Closes #1370.

src/preferences/preferences.cpp

@@ -47,6 +47,7 @@
 
 #ifdef Q_OS_WIN
 #include <ShlObj.h>
+#include <winreg.h>
 #endif
 
 #include "misc.h"
@@ -55,7 +56,6 @@
 
 Preferences* Preferences::m_instance = 0;
 
-
 Preferences::Preferences() : dirty(false), lock(QReadWriteLock::Recursive) {
   QIniSettings *settings = new QIniSettings;
 #ifndef Q_OS_MAC
@@ -1339,30 +1339,104 @@ void Preferences::disableRecursiveDownload(bool disable) {
 }
 
 #ifdef Q_OS_WIN
+namespace {
+QStringList getRegSubkeys(const HKEY &handle) {
+  QStringList keys;
+  DWORD subkeys_count = 0;
+  DWORD max_subkey_len = 0;
+  long res = ::RegQueryInfoKey(handle, NULL, NULL, NULL, &subkeys_count, &max_subkey_len, NULL, NULL, NULL, NULL, NULL, NULL);
+  if (res == ERROR_SUCCESS) {
+    max_subkey_len++; //For null character
+    LPTSTR key_name = new TCHAR[max_subkey_len];
+
+    for (uint i=0; i<subkeys_count; i++) {
+      res = ::RegEnumKeyEx(handle, 0, key_name, &max_subkey_len, NULL, NULL, NULL, NULL);
+      if (res == ERROR_SUCCESS)
+        keys.push_back(QString::fromWCharArray(key_name));
+    }
+    delete[] key_name;
+  }
+
+  return keys;
+}
+
+QString getRegValue(const HKEY &handle, const QString &name = QString()) {
+  QString end_result;
+  DWORD type = 0;
+  DWORD size = 0;
+  DWORD array_size = 0;
+
+  LPTSTR value_name = NULL;
+  if (!name.isEmpty()) {
+    value_name = new TCHAR[name.size()+1];
+    name.toWCharArray(value_name);
+    value_name[name.size()] = '\0';
+  }
+
+  // Discover the size of the value
+  ::RegQueryValueEx(handle, value_name, NULL, &type, NULL, &size);
+  array_size = size / sizeof(TCHAR);
+  if (size % sizeof(TCHAR))
+    array_size++;
+  array_size++; //For null character
+  LPTSTR value = new TCHAR[array_size];
+
+  long res = ::RegQueryValueEx(handle, value_name, NULL, &type, (LPBYTE)value, &size);
+  if (res == ERROR_SUCCESS) {
+    value[array_size] = '\0';
+    end_result = QString::fromWCharArray(value);
+  }
+
+  if (value_name)
+    delete[] value_name;
+  if (value)
+    delete[] value;
+
+  return end_result;
+}
+
+}
+
 QString Preferences::getPythonPath() {
-  QSettings reg_python("HKEY_LOCAL_MACHINE\\SOFTWARE\\Python\\PythonCore", QIniSettings::NativeFormat);
-  QStringList versions = reg_python.childGroups();
+  HKEY key_handle1;
+  long res = ::RegOpenKeyEx(HKEY_LOCAL_MACHINE, TEXT("SOFTWARE\\Python\\PythonCore"), 0, KEY_READ, &key_handle1);
+  if (res == ERROR_SUCCESS) {
+    QStringList versions = getRegSubkeys(key_handle1);
     qDebug("Python versions nb: %d", versions.size());
-  //versions = versions.filter(QRegExp("2\\..*"));
     versions.sort();
+
     while(!versions.empty()) {
-    const QString version = versions.takeLast();
+      const QString version = versions.takeLast()+"\\InstallPath";
+      HKEY key_handle2;
+      LPTSTR subkey = new TCHAR[version.size()+1];
+      version.toWCharArray(subkey);
+      subkey[version.size()] = '\0';
+
+      res = ::RegOpenKeyEx(key_handle1, subkey, 0, KEY_READ, &key_handle2);
+      delete[] subkey;
+      if (res == ERROR_SUCCESS) {
         qDebug("Detected possible Python v%s location", qPrintable(version));
-    QString path = reg_python.value(version+"/InstallPath/Default", "").toString();
+        QString path = getRegValue(key_handle2);
+        ::RegCloseKey(key_handle2);
         if (!path.isEmpty() && QDir(path).exists("python.exe")) {
           qDebug("Found python.exe at %s", qPrintable(path));
+          ::RegCloseKey(key_handle1);
           return path;
         }
       }
+      else
+        ::RegCloseKey(key_handle2);
+    }
+  }
+  ::RegCloseKey(key_handle1);
+
   // Fallback: Detect python from default locations
   QStringList supported_versions;
   supported_versions << "32" << "31" << "30" << "27" << "26" << "25";
   foreach (const QString &v, supported_versions) {
-    if (QFile::exists("C:/Python"+v+"/python.exe")) {
-      reg_python.setValue(v[0]+"."+v[1]+"/InstallPath/Default", QString("C:/Python"+v));
+    if (QFile::exists("C:/Python"+v+"/python.exe"))
       return "C:/Python"+v;
   }
-  }
   return QString::null;
 }