message: retain non-file flags when moving

The content-flags won't change, and the unread-flag can be re-calculated.

Add a unit test, and some small doc improvements.

Fixes #2831.

4 files changed, 33 insertions, 22 deletions

diff --git a/lib/message/mu-flags.hh b/lib/message/mu-flags.hh
index 8e424dd..ee01702 100644
--- a/lib/message/mu-flags.hh
+++ b/lib/message/mu-flags.hh
@@ -1,5 +1,5 @@
 /*
-** Copyright (C) 2022-2023 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
+** Copyright (C) 2022-2025 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
 **
 ** This program is free software; you can redistribute it and/or modify it
 ** under the terms of the GNU General Public License as published by the
@@ -86,7 +86,7 @@ enum struct MessageFlagCategory {
 };
 
 /**
- * Info about invidual message flags
+ * Info about individual message flags
  *
  */
 struct MessageFlagInfo {
@@ -373,9 +373,6 @@ flags_maildir_file(Flags flags)
 	return flags;
 }
 
-
-
-
 /**
  * Return flags, where flags = new_flags but with unmutable_flag in the
  * result the same as in old_flags
diff --git a/lib/message/mu-message.cc b/lib/message/mu-message.cc
index 3d4d2df..339abd1 100644
--- a/lib/message/mu-message.cc
+++ b/lib/message/mu-message.cc
@@ -881,6 +881,14 @@ Message::update_after_move(const std::string& new_path,
 	priv_->doc.add(Field::Id::Path, new_path);
 	priv_->doc.add(Field::Id::Changed, priv_->ctime);
 
+	// note: content-flags are retained from the existing; the unread flag
+	// is implied. only file-flags are allowed for new_flags; anything else
+	// is filtered-out
+
+	new_flags = flags_maildir_file(new_flags);
+	new_flags |= flags_filter(flags(), MessageFlagCategory::Content);
+	new_flags = imply_unread(new_flags);
+
 	set_flags(new_flags);
 
 	if (const auto res = set_maildir(sanitize_maildir(new_maildir)); !res)
diff --git a/lib/message/mu-message.hh b/lib/message/mu-message.hh
index 9be9096..c6b6917 100644
--- a/lib/message/mu-message.hh
+++ b/lib/message/mu-message.hh
@@ -1,5 +1,5 @@
 /*
-** Copyright (C) 2022-2024 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
+** Copyright (C) 2022-2025 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
 **
 ** This program is free software; you can redistribute it and/or modify it
 ** under the terms of the GNU General Public License as published by the
@@ -292,11 +292,10 @@ public:
 	 */
 	Flags flags() const { return document().flags_value(); }
 
-
 	/**
-	 * Update the flags for this message. This is useful for flags
-	 * that can only be determined after the message has been created already,
-	 * such as the 'personal' flag.
+	 * Update the flags for this message. This is useful for flags that can
+	 * only be determined after the message has been created already, such
+	 * as the 'personal' flag.
 	 *
 	 * @param flags new flags.
 	 */
@@ -366,11 +365,14 @@ public:
 	 */
 	const Sexp& sexp() const;
 
-	/*
-	 * And some non-const message, for updating an existing
-	 * message after a file-system move.
+	/**
+	 * Update the message after a move
+	 *
+	 * @param new_path the new file-system path; non-file flags are ignored
+	 * @param new_maildir the new maildir
+	 * @param new_flags the new flags
 	 *
-	 * @return Ok or an error.
+	 * @return Ok() or some error.
 	 */
 	Result<void> update_after_move(const std::string& new_path,
 				       const std::string& new_maildir,
diff --git a/lib/mu-store.hh b/lib/mu-store.hh
index 24130de..cc7946a 100644
--- a/lib/mu-store.hh
+++ b/lib/mu-store.hh
@@ -1,5 +1,5 @@
 /*
-** Copyright (C) 2024 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
+** Copyright (C) 2017-2025 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
 **
 ** This program is free software; you can redistribute it and/or modify it
 ** under the terms of the GNU General Public License as published by the
@@ -306,20 +306,24 @@ public:
 	};
 
 	/**
-	 * Move a message both in the filesystem and in the store. After a successful move, the
-	 * message is updated.
+	 * Move a message both in the filesystem and in the store.
+	 *
+	 * After a successful move, the message is updated. A moved message gets
+	 * a new doc-id, since the message-path is a unique-id for the message
 	 *
 	 * @param id the id for some message
 	 * @param target_mdir the target maildir (if any)
 	 * @param new_flags new flags (if any)
 	 * @param opts move options
 	 *
-	 * @return Result, either an IdPathVec with ids and paths for the moved message(s) or some
-	 * error. Note that in case of success at least one message is returned, and only with
-	 * MoveOptions::DupFlags can it be more than one.
+	 * @return Result, either an IdPathVec with ids and paths for the moved
+	 * message(s) or some error. Note that in case of success at least one
+	 * message is returned, and only with MoveOptions::DupFlags can it be
+	 * more than one.
 	 *
-	 * The first element of the IdPathVec, is the main message that got move; any subsequent
-	 * (if any) are the duplicate paths, sorted by path-name.
+	 * The first element of the IdPathVec, is the main message that got
+	 * move; any subsequent (if any) are the duplicate paths, sorted by
+	 * path-name.
 	 */
 	Result<IdPathVec> move_message(Store::Id id,
 				       Option<const std::string&> target_mdir = Nothing,