Cross platform common paths

[telenieko]

When working on desktop platforms it is a quite common need to get path's to certain standards that vary platform to platform, for example:

• The user home directory, which can be retrieved from either HOME or USERPROFILE environment variables depending on the platform.
• The application configuration path, which could be...
  • ~/.<my app> or ~/.config/<my app> on Linux
  • ~/.<my app> on macOS
  • %APPDATA%/<my app> on windows
• Location for caches (%TEMP% on windows?, .cache/<my app>, ...)
• Temporary files
• Downloads folder

Right now dart provides a cross-platform solution for one of those, systemTemp but none of the others.

While the core libraries do not provide such functionality (which, being truthful, probably no language's standard library provides) there is a risk of every app finding it's own solution which may be better, worse, secure, insecure or full of bugs and unexpected corner-cases.

Knowing where an app is supposed to keeps its caches & configurations or where the user home folder lives is not only platform specific but may also vary depending on the distribution method (App Store & Microsoft Store do have specific recommendations / requirements about that).

Also, it would be risky to expect every developer to know all the appropiate paths on all platforms and stores.

Flutter team has started to walk on this direction with the xdg_directories package, though that's not cross-platform.

So, bottom line, feature request: provide a cross-platform way to retrieve Directory instances of common / standard folders. Either in core or as an official package.

References,

• The SO question linked above has >2k views.
• Issue Provide a way to get current user's home directory #498 was about HOME and was closed referring to Envrionment, which is not crossplatform.
• Fluter's xdg_directories package

My current dart version is : Dart SDK version: 2.16.1 (stable) (Tue Feb 8 12:02:33 2022 +0100) on "windows_x64".