Accounts with user ids containing forward slashes can't be loaded correctly

[TobiasFella]

Reported as https://bugs.kde.org/show_bug.cgi?id=491252

The user id is used as a key for QSettings, which uses forward slashes as separators. When listing the account, wrong groups are thus returned.

We need to somehow come up with a way of escaping forward slashes while not breaking existing logged-in accounts (at least those that do not contain forward slashes; for the other ones, logging in again is probably inevitable but also not problematic. I haven't been able to come up with a nice way to do that yet.

[KitsuneRal]

I was about to say that forward slashes in user ids are a deprecated legacy but no ;(
Why can't we "simply" percent-encode the forward slashes though?

[KitsuneRal]

Okay, I think I understand at least a part of the challenge - there's plenty of places where they key is joined with the group name and Settings already gets the full key name, with "right" and "wrong" slashes indistinguishable from each other. Otherwise, percent-encoded slashes are double-percent-encoded by QSettings in the actually stored keys (if I encode / to %2F what actually gets written is %252F) but that's not a big deal as long as it's consistently used to match/store/remove keys I think?

[KitsuneRal]

A bigger problem is with SettingsGroup, specifically childGroups() and remove(), used in both Quaternion and NeoChat to respectively collect and remove accounts from the settings. The problem is that not all SettingsGroups are groups of accounts and we might not want to aggressively unescape keys from any group. This can be worked around for now by checking directly whether a given group is named Accounts; and for 0.10 we can make a dedicated API for the accounts group, and even warn in the logs at runtime if someone tries to use SettingsGroup(u"Accounts"_s).