desktop: Do not store logs in config directory

[kjarosh]

Logs are non-essential and can be removed, contrary to config files. This PR changes the log directory from config dir to cache dir.

Platform	Old Path	New Path
Linux	~/.config/ruffle/*.log	~/.cache/ruffle/log/*.log
macOS	~/Library/Application Support/ruffle/*.log	~/Library/Caches/ruffle/log/*.log
Windows	C:\Users\Alice\AppData\Local\ruffle\*.log	C:\Users\Alice\AppData\Local\ruffle\log\*.log

Old log files will be migrated to the new path on startup.

[Dinnerbone]

I like it, my only nit is why log and not logs?

[kjarosh]

why log and not logs?

I guess the reason is the subconscious desire to stick to conventions used in the Filesystem Hierarchy Standard: /var/log not /var/logs, /usr/include not /usr/includes, /usr/lib not /usr/libs, etc.

[torokati44]

Some say that logs rather belong to $XDG_STATE_HOME (usually $HOME/.local/state), but it's a Linux-only thing (https://docs.rs/dirs/5.0.1/dirs/fn.state_dir.html), and the consensus seems to be that the second best place for it is indeed the cache directory.
The migration part is a nice touch! Although, maybe if the destination file already exists, it shouldn't be overwritten? 🤔

[kjarosh]

Some say that logs rather belong to $XDG_STATE_HOME

I know that there's no obvious place to store log files on Linux (except /var/log for system services). Usually you'd use syslog for the purpose of persisting logs, but I'm not sure about flatpak though.

However, the goal of this PR is not to find the best place to persist logs, but rather to remove them from the obviously wrong place. If they are stored in the config dir, the user has no way of removing them (except manually knowing which files may be removed). That will get exceptionally bad if someone chooses "with timestamp" which will make the config directory grow indefinitely in size.

Although, maybe if the destination file already exists, it shouldn't be overwritten?

I don't think that matters much, logs are migrated before we even try to write to the new directory, and the goal of the migration is not strictly to preserve the logs, but rather to get them out of the config dir.

The file ruffle.log is truncated on start anyway and overwriting logs with timestamps is virtually impossible, unless you're Flash (the other one) and you have an exceptionally mischievous computer.

[torokati44]

Thank you! ^^