Defaults

From our survey of other simlar packages, we've seen a range of approaches. Trying to take the best of those, these are the defaults that BaseDirs.jl uses.

Base directories

Common Name	EnvVar	Linux	MacOS	Windows (KnownPath)
User data	`XDG_DATA_HOME`	`~/.local/share`	`~/Library/Application Support`	`RoamingAppData`
System data	`XDG_DATA_DIRS`	`/usr/local/share`, `/usr/share`	`/Library/Application Support`	`ProgramData`
User config	`XDG_CONFIG_HOME`	`~/.config`	`~/Library/Application Support`	`RoamingAppData`
System config	`XDG_CONFIG_DIRS`	`/etc/xdg`	`/Library/Application Support`	`ProgramData`
State	`XDG_STATE_HOME`	`~/.local/state`	`~/Library/Application Support`	`LocalAppData`
User executables	`XDG_BIN_HOME` ^[binhome]	`~/.local/bin`	`~/.local/bin` or `/opt/local/bin` or `/usr/local/bin`	`~\bin` or `RoamingAppData\bin` or `AppData\bin` or `pwd()`
Cache	`XDG_CACHE_HOME`	`~/.cache`	`~/Library/Caches/`	`LocalAppData\cache`
Runtime	`XDG_RUNTIME_DIR`	`/run/user/$UID`	`~/Library/Application Support`	`LocalAppData`

User directories

Common Name	EnvVar	Linux^{[xdguserdirs]}	MacOS	Windows (KnownPath)
Desktop	`XDG_DESKTOP_DIR`	`~/Desktop`	`~/Desktop`	`Desktop`
Download	`XDG_DOWNLOAD_DIR`	`~/Downloads`	`~/Downloads`	`Downloads`
Documents	`XDG_DOCUMENTS_DIR`	`~/Documents`	`~/Documents`	`Documents`
Music	`XDG_MUSIC_DIR`	`~/Music`	`~/Music`	`Music`
Pictures	`XDG_PICTURES_DIR`	`~/Pictures`	`~/Pictures`	`Pictures`
Videos	`XDG_VIDEOS_DIR`	`~/Videos`	`~/Movies`	`Videos`
Templates	`XDG_TEMPLATES_DIR`	`~/Templates`	`~/Templates`	`Templates`
Public	`XDG_PUBLICSHARE_DIR`	`~/Public`	`~/Public`	`Public`

Project directories

Project paths

A project path string (henceforth given by the Project placeholder) is formatted according to the following bits of information:

Qualifier (only used on mac), which defaults to org
Organisation/Company, which defaults to julia
Application/Project name, which must be provided.

The operating system specific project path is composed as follows:

System	Project path format	Example
Linux	`$Name`	`contraption`
MacOS	`$Qualifier.$Organisation.$Name`	`com.ACME.contraption`
Windows	`$Organisation\$Name`	`ACME\contraption`

Project directory template

Common Name	Linux	MacOS	Windows
User data	`$(User data)/$Project`	`$(User data)/$Project`	`$(User data)\$Project\data`
System data	`$(System data)/$Project`	`$(System data)/$Project`	`$(System data)\$Project\data`
User config	`$(User config)/$Project`	`$(User config)/$Project`	`$(User config)\$Project\config`
System config	`$(System config)/$Project`	`$(System config)/$Project`	`$(System config)\$Project\config`
Cache	`$(Cache)/$Project`	`$(Cache)/$Project`	`$(Cache)\$Project\cache`
State	`$(State)/$Project`	`$(State)/$Project`	`$(State)\$Project\state`

Extra directories

Common name	Linux	MacOS	Windows
Fonts	`$(User data)/fonts`, `~/.fonts`, `$(System data)/fonts`	`~/Library/Fonts`, `/Library/Fonts`, `/System/Library/Fonts`, `/Network/Library/Fonts`	`Fonts`
Applications	`$(User data)/applications`, `$(System data)/applications`	`/Applications`	`Programs`, `CommonPrograms`

binhomeWhile XDG_BIN_HOME is not yet standard, it seems like the most likely name to be given to ~/.local/bin (see this issue), and I think it is worth having something rather than nothing.
xdguserdirsIn accordance with the xdg-user-dirs documentation, the system and user user-dirs.dirs files are checked before using the defaults.