feat: Enable OnlyFetchMvbox by default (#7190)

This is a replacement for 2260156c40 "feat: Don't fetch messages from
unknown folders", but limited to the case with `MvboxMove` enabled. It's enabled by default, so most
users still gain from not fetching messages from unknown folders.

src/config.rs

@@ -169,7 +169,7 @@ pub enum Config {
     ///
     /// This will not entirely disable other folders, e.g. the spam folder will also still
     /// be scanned for new messages.
-    #[strum(props(default = "0"))]
+    #[strum(props(default = "1"))]
     OnlyFetchMvbox,
 
     /// Whether to show classic emails or only chat messages.

src/imap/imap_tests.rs

@@ -122,8 +122,9 @@ async fn check_target_folder_combination(
     t.ctx
         .set_config(Config::ConfiguredSentboxFolder, Some("Sent"))
         .await?;
+    t.ctx.set_config_bool(Config::MvboxMove, mvbox_move).await?;
     t.ctx
-        .set_config(Config::MvboxMove, Some(if mvbox_move { "1" } else { "0" }))
+        .set_config_bool(Config::OnlyFetchMvbox, mvbox_move)
         .await?;
 
     if accepted_chat {

src/sql/migrations.rs

@@ -1342,6 +1342,20 @@ CREATE INDEX gossip_timestamp_index ON gossip_timestamp (chat_id, fingerprint);
         .await?;
     }
 
+    inc_and_check(&mut migration_version, 139)?;
+    if dbversion < migration_version {
+        // `OnlyFetchMvbox` is now 1 by default to avoid scanning unknown folders. But if the user
+        // disabled `MvboxMove`, we have to keep `OnlyFetchMvbox` unset so that Inbox is watched.
+        sql.execute_migration(
+            "INSERT OR IGNORE INTO config (keyname, value)
+             SELECT 'only_fetch_mvbox', '0'
+             FROM config WHERE keyname='mvbox_move' AND value='0'
+            ",
+            migration_version,
+        )
+        .await?;
+    }
+
     let new_version = sql
         .get_raw_config_int(VERSION_CFG)
         .await?