examples: add minimal_lsp.rs and FIFO test script

[shashforge]

Adds a single example, examples/minimal_lsp.rs, plus a tiny FIFO test script.
The sample now shows:

- completion textDocument/completion
- hover textDocument/hover
- goto-definition textDocument/definition
- full-doc formatting (rustfmt) textDocument/formatting
- dummy diagnostics textDocument/publishDiagnostics
- UTF-8 offsetEncoding in the initialize response

Quick test

one-shot, all nine packets

cargo build --example minimal_lsp
target/debug/examples/minimal_lsp < examples/nine_packets.txt

Also includes examples/manual_test.sh, a tiny FIFO script that sends the canonical 9 LSP packets so the server can be verified from two terminals.

Two-terminal test

mkfifo /tmp/lsp_pipe
terminal A
cat /tmp/lsp_pipe | cargo run --example minimal_lsp
terminal B
bash examples/manual_test.sh # pumps the same nine packets

We should see, in order: capabilities → diagnostics → completion → hover → definition → formatting → shutdown.
(anyhow stays under [dev-dependencies]).

Fixes #20017

[shashforge]

Hi @ShoyuVanilla @lnicola ,

Thank you for the helpful guidance on my last attempt on #20187
As you suggested, I’ve folded the logic from goto_def.rs and my earlier demo into a single file, examples/minimal_lsp.rs.
The new example now covers

• completion
• hover
• goto-definition
• full-file formatting via rustfmt
• a dummy diagnostic push
• UTF-8 offsetEncoding in the initialize

I’ve also added a tiny FIFO helper (examples/manual_test.sh) to replay the nine canonical packets, so the whole round-trip can be tested in two terminals.
Whenever you have a moment, I’d really appreciate another look.
Thanks again for your time and feedback!

— Shashi

[ShoyuVanilla]

Thanks! I'll take a look before not too late 😅

[ShoyuVanilla]

Overally looks good but some nits and a question:

[shashforge]

Hi @ShoyuVanilla

Thanks so much for the careful review!

1. Header tidy-up – I removed the SPDX line and the banner underline.
2. goto_def.rs mention – dropped, since that file is gone now.
3. manual_test.sh – added a short note that the FIFO only feeds stdin, so the code path is the same as a direct pipe.

Ran cargo fmt; the example builds and clippy is clean.

If the extra script still feels like overkill, I’m happy to delete it and rely on the one-liner here-doc instead—just say the word.

Really appreciate your time and feedback. Let me know if there’s anything else you’d like tweaked!

[ShoyuVanilla]

Thanks! Sorry for being too picky on this PR. As this is adding an example that serves as a documentation for newcomers, I had to be sensitive on accuracy 😅

[shashforge]

Thanks! Sorry for being too picky on this PR. As this is adding an example that serves as a documentation for newcomers, I had to be sensitive on accuracy 😅

Absolutely, and thanks again for the careful review — it only makes the example stronger.

If there are other bite-sized issues or examples that could use a fresh set of eyes, I’d be happy to tackle them next. I’m already browsing the issue tracker, but please feel free to point me toward anything you think would be especially helpful for the project. I’m keen to contribute wherever it adds the most value.