fix: Include exercises folder in the project structure behind a feature

[x-hgg-x]

closes #859
closes #913
closes #942

Related to #443 and #289.

This allows rust-analyzer to work normally after adding the setting "rust-analyzer.cargo.features": ["exercises"].

[shadows-withal]

Does this require an adjustment on the user's side (just to make sure I'm understanding this correctly)? If so, can this specific configuration change for rust-analyzer be done per-project? I'm not too familiar with its configuration.

[x-hgg-x]

Yes you can set this setting per-project.
For Visual Studio Code you create the file .vscode/settings.json with the content:

{
    "rust-analyzer.cargo.features": ["exercises"],
}

It should also work with other IDEs if they allow to set cargo features.

[x-hgg-x]

It also works in IntelliJ Rust without any settings since the plugin seems to run cargo with the --all-features parameter by default.

[fabianlupa]

Found this PR after having no analysis in CLion and applying the patch seems to have fixed it perfectly without any additional configuration.

[shadows-withal]

Okay, so as long as you enable running either with all features or specifically that feature it works... I think that's a good enough compromise for us, given that we don't use the standard Rust directory layout in the first place. I'll merge this and document it in the README file.

[shadows-withal]

@all-contributors please add @x-hgg-x for code

[allcontributors]

@diannasoreil

I've put up a pull request to add @x-hgg-x! 🎉

[alexrecuenco]

It seems that this fix was later removed in ed0f278 for 5.x (ed0f278)

Any reason why?

Any documentation in what rustlings expect us to do with intellisense on the 5.x versions?

[shadows-withal]

@alexrecuenco This was our first implementation of LSP functionality, which we ended up removing in favor of https://github.com/rust-lang/rustlings#enabling-rust-analyzer.