maildir: remove filename encoded UID when moving messages

The built-in maildir.Dir.Move method performs an OS level file rename,
which allows for preserving file creation time. Commit c98f704874
("move: enable MoveMessages from msgstore") enabled the use of the Move
method for maildir. One particular maildir synchronizer (isync/mbsync)
encodes the UID within the filename of the email and cannot recover if
the UID is preserved during a move. mbsync encodes filenames like so:

	/path/to/email/{maildir-key},U={uid}:2,S

OfflineIMAP encodes the UID within the filename, but also encodes a hash
of the originating folder so that it can recover from a move without a
rename of the underlying file. OfflineIMAP encodes like so:

	/path/to/email{maildir-key},U={uid},FMD5={folder-hash}:2,S

Remove encoded UIDs of the form `,U={uid}` from filenames to prevent
sync issues.

Fixes: https://todo.sr.ht/~rjarry/aerc/75
Fixes: c98f704874 ("move: enable MoveMessages from msgstore")
Signed-off-by: Tim Culverhouse <tim@timculverhouse.com>
Acked-by: Robin Jarry <robin@jarry.cc>

worker/maildir/container.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"regexp"
 	"sort"
 	"strings"
 
@@ -12,6 +13,10 @@ import (
 	"git.sr.ht/~rjarry/aerc/lib/uidstore"
 )
 
+// uidReg matches filename encoded UIDs in maildirs synched with mbsync or
+// OfflineIMAP
+var uidReg = regexp.MustCompile(`,U=\d+`)
+
 // A Container is a directory which contains other directories which adhere to
 // the Maildir spec
 type Container struct {
@@ -222,6 +227,12 @@ func (c *Container) moveMessage(dest maildir.Dir, src maildir.Dir, uid uint32) e
 	if !ok {
 		return fmt.Errorf("could not find key for message id %d", uid)
 	}
-	err := src.Move(dest, key)
-	return err
+	path, err := src.Filename(key)
+	if err != nil {
+		return fmt.Errorf("could not find path for message id %d", uid)
+	}
+	// Remove encoded UID information from the key to prevent sync issues
+	name := uidReg.ReplaceAllString(filepath.Base(path), "")
+	destPath := filepath.Join(string(dest), "cur", name)
+	return os.Rename(path, destPath)
 }