I've noticed a few bugs related to folder naming. Mainly these seem to be due to a lack of clarity about what names are valid where and how names in various different places map to each other. So this bug is a place to try and document and tidy things up.

Here are my notes so far on the various flavours of folder names in use:

Places where folder names are used:

Folder Name

• The 'canonical'/internal name of the folder.
• in nsIMsgFolder name attribute
• Usually the same as the user-facing name (but there is a prettyName attr too)
• Used to derive URI in nsIMsgFolder getURI() implementations.
• There is some special-case handling for certain folder names - case tweaking, localisation etc. See nsMsgDBFolder::SetPrettyName() for an example.
• There is also abbrieviatedName, which uses account-specific rules to shorten long names. I think only Newsfolders use it (eg "comp.sys.lang.basic" => "c.s.l.basic").

User-facing names

• As displayed in the folder tree UI panel.
• Should probably be able to display any printable characters: non-latin chars, '/','' etc.
• TODO: look in the UI code to see where display name is taken from.

MailStore (ie mbox/maildir on filesystem)

• The names of files and directories on disk.
• Allowed characters depends on OS
• Case-sensitivity depends on OS
• Some names have special significance? "INBOX", "Trash" etc. Sets flags on the folder.
• Folder discovery iterates over filesystem names, and uses those names for the UI
  => some names are tweaked/localised when mapped to UI, eg "INBOX" -> "Inbox"
  => TODO: where is this mapping performed?
• should be able to copy folders across OSes? (ie should enforce a common
  subset of naming rules? Treat "Stuff" and "stuff" as the same folder on case-sensitive filesystems?)
• TODO: link to unix, windows filesystem naming rules
• Numeric suffix added to deduplicate... eg "INBOX-1" (TODO: why is this needed? How does it work with folder discovery?)

IMAP folders

• TB queries IMAP server to find remote folders.
• Base IMAP has ascii names, but extensions handle full unicode (TODO: confirm)
• Takes time to ask server. Usually, if there's a mailstore (filesystem) folder that will be picked up first.
• Missing mailstore folders are created as needed (TODO: identify code that does this). Eg, for a new TB install.

Folder URIs

• Full identity of a folder within TB
• stored in VirtualFolders.dat, and elsewhere
• what are the current encoding rules? What should they be?

=> I think the folder parts of the URI should be UTF-8, then percent-encoded. For example, you should be able to have a folder name in Japanese, say, with a '/' in it eg: "はい/いいえ" ("yes/no").

VirtualFolders.dat

• Contains URI of virtual folder to create
• Upon loading, creates a nsDBMsgFolder with name and parent folder based upon URI
• see nsMsgAccountManager::LoadVirtualFolders() and nsMsgAccountManager::SaveVirtualFolders().

Ahh - doh. Was going through adding related bugs and Just noticed Bug 124287, which overlaps a lot with this (and already has a long dependency list)... Perhaps I should move my notes over to there and close this one?

The meta bug is a good move, but you should add all the dependents here or in the other bug, like bug 1568845 and bug 1512053 and many more. I'll leave it to you to organise.

I think this bug overlaps too much with Bug 124287, so I'm going to move over to there instead (adding my notes and any new name-related bugs I find).