[partition] reduce warnings with unsafe-option

- Move variables closer to where they are needed
- Do the winnowing / selection always, but in unsafe mode return
  the un-winnowed list of devices
- Massage build documentation a little

src/modules/partition/CMakeLists.txt

@@ -8,8 +8,9 @@
 # want to allow unsafe partitioning choices (e.g. doing things to the
 # current disk). Set DEBUG_PARTITION_UNSAFE to allow that (it turns off
 # some filtering of devices). If you **do** allow unsafe partitioning,
-# it will error out unless you **also** switch **off** DEBUG_PARTITION_LAME,
-# at which point you are welcome to shoot yourself in the foot.
+# it will error out at runtime unless you **also** switch **off**
+# DEBUG_PARTITION_LAME, at which point you are welcome to shoot
+# yourself in the foot.
 option( DEBUG_PARTITION_UNSAFE "Allow unsafe partitioning choices." OFF )
 option( DEBUG_PARTITION_LAME   "Unsafe partitioning will error out on exec." ON )
 

src/modules/partition/core/DeviceList.cpp

@@ -118,8 +118,6 @@ erase( DeviceList& l, DeviceList::iterator& it )
 QList< Device* >
 getDevices( DeviceType which )
 {
-    bool writableOnly = ( which == DeviceType::WritableOnly );
-
     CoreBackend* backend = CoreBackendManager::self()->backend();
 #if defined( WITH_KPMCORE4API )
     DeviceList devices = backend->scanDevices( /* not includeReadOnly, not includeLoopback */ ScanFlag( 0 ) );
@@ -129,14 +127,18 @@ getDevices( DeviceType which )
 
 #ifdef DEBUG_PARTITION_UNSAFE
     cWarning() << "Allowing unsafe partitioning choices." << devices.count() << "candidates.";
+    DeviceList unsafeDevices = devices;
 #ifdef DEBUG_PARTITION_LAME
     cDebug() << Logger::SubEntry << "it has been lamed, and will fail.";
 #endif
-#else
+#endif
+
     cDebug() << "Removing unsuitable devices:" << devices.count() << "candidates.";
 
+    bool writableOnly = ( which == DeviceType::WritableOnly );
     // Remove the device which contains / from the list
     for ( DeviceList::iterator it = devices.begin(); it != devices.end(); )
+    {
         if ( !( *it ) )
         {
             cDebug() << Logger::SubEntry << "Skipping nullptr device";
@@ -166,9 +168,13 @@ getDevices( DeviceType which )
         {
             ++it;
         }
-#endif
-
+    }
+    cDebug() << Logger::SubEntry << "there are" << devices.count() << "devices left.";
+#ifdef DEBUG_PARTITION_UNSAFE
+    return unsafeDevices;
+#else
     return devices;
+#endif
 }
 
 }  // namespace PartUtils