Make return type of Image::mv an enum

Replace named constants with enum to improve type-safety and make
exhausiveness checks possible.

Note, that since this enum never pass FFI border, its numeric values
does not need to be specified explicitly and can be left on compiler's
discretion.

src/imap.rs

@@ -19,6 +19,14 @@ use crate::param::Params;
 
 const DC_IMAP_SEEN: usize = 0x0001;
 
+#[derive(Debug, Display, Clone, Copy, PartialEq, Eq)]
+pub enum ImapResult {
+    Failed,
+    RetryLater,
+    AlreadyDone,
+    Success,
+}
+
 pub const DC_SUCCESS: usize = 3;
 pub const DC_ALREADY_DONE: usize = 2;
 pub const DC_RETRY_LATER: usize = 1;
@@ -1130,12 +1138,12 @@ impl Imap {
         uid: u32,
         dest_folder: S2,
         dest_uid: &mut u32,
-    ) -> usize {
-        let mut res = DC_RETRY_LATER;
+    ) -> ImapResult {
+        let mut res = ImapResult::RetryLater;
         let set = format!("{}", uid);
 
         if uid == 0 {
-            res = DC_FAILED;
+            res = ImapResult::Failed;
         } else if folder.as_ref() == dest_folder.as_ref() {
             info!(
                 context,
@@ -1145,7 +1153,7 @@ impl Imap {
                 dest_folder.as_ref()
             );
 
-            res = DC_ALREADY_DONE;
+            res = ImapResult::AlreadyDone;
         } else {
             info!(
                 context,
@@ -1165,7 +1173,7 @@ impl Imap {
                 let moved = if let Some(ref mut session) = &mut *self.session.lock().unwrap() {
                     match session.uid_mv(&set, &dest_folder) {
                         Ok(_) => {
-                            res = DC_SUCCESS;
+                            res = ImapResult::Success;
                             true
                         }
                         Err(err) => {
@@ -1205,22 +1213,22 @@ impl Imap {
                             warn!(context, "Cannot mark message as \"Deleted\".",);
                         }
                         self.config.write().unwrap().selected_folder_needs_expunge = true;
-                        res = DC_SUCCESS;
+                        res = ImapResult::Success;
                     }
                 }
             }
         }
 
-        if res == DC_SUCCESS {
+        if res == ImapResult::Success {
             // TODO: is this correct?
             *dest_uid = uid;
         }
 
-        if res == DC_RETRY_LATER {
+        if res == ImapResult::RetryLater {
             if self.should_reconnect() {
-                DC_RETRY_LATER
+                ImapResult::RetryLater
             } else {
-                DC_FAILED
+                ImapResult::Failed
             }
         } else {
             res

src/job.rs

@@ -247,13 +247,13 @@ impl Job {
                         &dest_folder,
                         &mut dest_uid,
                     ) {
-                        DC_RETRY_LATER => {
+                        ImapResult::RetryLater => {
                             self.try_again_later(3i32, None);
                         }
-                        DC_SUCCESS => {
+                        ImapResult::Success => {
                             dc_update_server_uid(context, &msg.rfc724_mid, &dest_folder, dest_uid);
                         }
-                        DC_FAILED | DC_ALREADY_DONE | _ => {}
+                        ImapResult::Failed | ImapResult::AlreadyDone => {}
                     }
                 }
             }
@@ -401,8 +401,8 @@ impl Job {
                 }
                 let dest_folder = context.sql.get_config(context, "configured_mvbox_folder");
                 if let Some(dest_folder) = dest_folder {
-                    if 1 == inbox.mv(context, folder, uid, dest_folder, &mut dest_uid)
-                        as libc::c_uint
+                    if ImapResult::RetryLater
+                        == inbox.mv(context, folder, uid, dest_folder, &mut dest_uid)
                     {
                         self.try_again_later(3, None);
                     }