Add warning about rust-analyzer not working if you clone and use the repo directly

[MadLittleMods]

Add warning about rust-analyzer not working if you clone and use the repo directly.

Yes, you are right, if you just clone the repository and try to edit the exercises, the language server will not work. This is one downside of the current approach. But this only affects developing exercises.

The new method of doing Rustlings is to install Rustlings using cargo install rustlings (not published yet), then running rustlings init. No repo cloning happens. Instead, the directory rustlings/ will be created where you find the exercises. The language server works there out of the box :)

I need to add a warning when people try to work on the exercises from the repository. Thanks pointing this out.

-- @mo8it, #1935 (comment)

Reproduction steps

Personally, I also fell into this trap since I would prefer to just run the thing from source than install something on my system.

1. Clone the repo: git clone [email protected]:rust-lang/rustlings.git
2. Start Rustlings: cargo run
3. Open VSCode and notice that rust-analyzer and lsp hints don't pop up
4. Google and find StackOverflow answers that mention rustlings lsp to setup lsp support
5. But rustlings lsp doesn't exist anymore and the changelog mentions that it should be supported out of the box. It's also confusing because the rustlings repo has it's own Cargo.toml with include = [... "/exercises/", ...] which to my newbie Rust eyes, seems like it might cover it and makes me think, this is supposed to work.
6. Eventually, I saw Use Cargo.toml instead of rust-project.json #1935 linked somewhere and it mentions this exact problem

Dev notes

• Previous rustlings lsp command: Add lsp command to fix rust-analyzer #1026
• The changelog says "LSP support out of the box", https://github.com/rust-lang/rustlings/blob/main/CHANGELOG.md#lsp-support-out-of-the-box

[mo8it]

I agree that we should add something to the README for this, but the addition should tell people to not clone the repository and instead follow the instructions above. A simple warning should be enough. Something like this:

"Don't try to clone the repository to do the exercises! Rust-Analyzer won't work in that case. Please follow the instructions above instead."

[MadLittleMods]

I've used caution but feel free to nit to warning or any other.

[MadLittleMods]

Updated to your exact wording ✅

I've kept the extra "Why?" background in a collapsible section since it feels like it adds a little bit of something that makes it more understandable and convincing. Happy to remove to get this shipped if you prefer.