src/tools/rust-analyzer/lib/lsp-server/examples/minimal_lsp.rs - third_party/rust - Git at Google

 //! Minimal Language‑Server‑Protocol example: **`minimal_lsp.rs`**
 //! =============================================================
 //!
 //! | ↔ / ← | LSP method | What the implementation does |
 //! |-------|------------|------------------------------|
 //! | ↔ | `initialize` / `initialized` | capability handshake |
 //! | ← | `textDocument/publishDiagnostics` | pushes a dummy info diagnostic whenever the buffer changes |
 //! | ← | `textDocument/definition` | echoes an empty location array so the jump works |
 //! | ← | `textDocument/completion` | offers one hard‑coded item `HelloFromLSP` |
 //! | ← | `textDocument/hover` | shows *Hello from minimal_lsp* markdown |
 //! | ← | `textDocument/formatting` | pipes the doc through **rustfmt** and returns a full‑file edit |
 //!
 //! ### Quick start
 //! ```bash
 //! cd rust-analyzer/lib/lsp-server
 //! cargo run --example minimal_lsp
 //! ```
 //!
 //! ### Minimal manual session (all nine packets)
 //! ```no_run
 //! # 1. initialize - server replies with capabilities
 //! Content-Length: 85

 //! {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"capabilities":{}}}
 //!
 //! # 2. initialized - no response expected
 //! Content-Length: 59

 //! {"jsonrpc":"2.0","method":"initialized","params":{}}
 //!
 //! # 3. didOpen - provide initial buffer text
 //! Content-Length: 173

 //! {"jsonrpc":"2.0","method":"textDocument/didOpen","params":{"textDocument":{"uri":"file:///tmp/foo.rs","languageId":"rust","version":1,"text":"fn  main( ){println!(\"hi\") }"}}}
 //!
 //! # 4. completion - expect HelloFromLSP
 //! Content-Length: 139

 //! {"jsonrpc":"2.0","id":2,"method":"textDocument/completion","params":{"textDocument":{"uri":"file:///tmp/foo.rs"},"position":{"line":0,"character":0}}}
 //!
 //! # 5. hover - expect markdown greeting
 //! Content-Length: 135

 //! {"jsonrpc":"2.0","id":3,"method":"textDocument/hover","params":{"textDocument":{"uri":"file:///tmp/foo.rs"},"position":{"line":0,"character":0}}}
 //!
 //! # 6. goto-definition - dummy empty array
 //! Content-Length: 139

 //! {"jsonrpc":"2.0","id":4,"method":"textDocument/definition","params":{"textDocument":{"uri":"file:///tmp/foo.rs"},"position":{"line":0,"character":0}}}
 //!
 //! # 7. formatting - rustfmt full document
 //! Content-Length: 157

 //! {"jsonrpc":"2.0","id":5,"method":"textDocument/formatting","params":{"textDocument":{"uri":"file:///tmp/foo.rs"},"options":{"tabSize":4,"insertSpaces":true}}}
 //!
 //! # 8. shutdown request - server acks and prepares to exit
 //! Content-Length: 67

 //! {"jsonrpc":"2.0","id":6,"method":"shutdown","params":null}
 //!
 //! # 9. exit notification - terminates the server
 //! Content-Length: 54

 //! {"jsonrpc":"2.0","method":"exit","params":null}
 //! ```
 //!

 use std::{error::Error, io::Write};

 use rustc_hash::FxHashMap; // fast hash map
 use std::process::Stdio;
 use toolchain::command; // clippy-approved wrapper

 #[allow(clippy::print_stderr, clippy::disallowed_types, clippy::disallowed_methods)]
 use anyhow::{Context, Result, anyhow, bail};
 use lsp_server::{Connection, Message, Request as ServerRequest, RequestId, Response};
 use lsp_types::notification::Notification as _; // for METHOD consts
 use lsp_types::request::Request as _;
 use lsp_types::{
     CompletionItem,
     CompletionItemKind,
     // capability helpers
     CompletionOptions,
     CompletionResponse,
     Diagnostic,
     DiagnosticSeverity,
     DidChangeTextDocumentParams,
     DidOpenTextDocumentParams,
     DocumentFormattingParams,
     Hover,
     HoverContents,
     HoverProviderCapability,
     // core
     InitializeParams,
     MarkedString,
     OneOf,
     Position,
     PublishDiagnosticsParams,
     Range,
     ServerCapabilities,
     TextDocumentSyncCapability,
     TextDocumentSyncKind,
     TextEdit,
     Url,
     // notifications
     notification::{DidChangeTextDocument, DidOpenTextDocument, PublishDiagnostics},
     // requests
     request::{Completion, Formatting, GotoDefinition, HoverRequest},
 }; // for METHOD consts

 // =====================================================================
 // main
 // =====================================================================

 #[allow(clippy::print_stderr)]
 fn main() -> std::result::Result<(), Box<dyn Error + Sync + Send>> {
     log::error!("starting minimal_lsp");

     // transport
     let (connection, io_thread) = Connection::stdio();

     // advertised capabilities
     let caps = ServerCapabilities {
         text_document_sync: Some(TextDocumentSyncCapability::Kind(TextDocumentSyncKind::FULL)),
         completion_provider: Some(CompletionOptions::default()),
         definition_provider: Some(OneOf::Left(true)),
         hover_provider: Some(HoverProviderCapability::Simple(true)),
         document_formatting_provider: Some(OneOf::Left(true)),
         ..Default::default()
     };
     let init_value = serde_json::json!({
         "capabilities": caps,
         "offsetEncoding": ["utf-8"],
     });

     let init_params = connection.initialize(init_value)?;
     main_loop(connection, init_params)?;
     io_thread.join()?;
     log::error!("shutting down server");
     Ok(())
 }

 // =====================================================================
 // event loop
 // =====================================================================

 fn main_loop(
     connection: Connection,
     params: serde_json::Value,
 ) -> std::result::Result<(), Box<dyn Error + Sync + Send>> {
     let _init: InitializeParams = serde_json::from_value(params)?;
     let mut docs: FxHashMap<Url, String> = FxHashMap::default();

     for msg in &connection.receiver {
         match msg {
             Message::Request(req) => {
                 if connection.handle_shutdown(&req)? {
                     break;
                 }
                 if let Err(err) = handle_request(&connection, &req, &mut docs) {
                     log::error!("[lsp] request {} failed: {err}", &req.method);
                 }
             }
             Message::Notification(note) => {
                 if let Err(err) = handle_notification(&connection, &note, &mut docs) {
                     log::error!("[lsp] notification {} failed: {err}", note.method);
                 }
             }
             Message::Response(resp) => log::error!("[lsp] response: {resp:?}"),
         }
     }
     Ok(())
 }

 // =====================================================================
 // notifications
 // =====================================================================

 fn handle_notification(
     conn: &Connection,
     note: &lsp_server::Notification,
     docs: &mut FxHashMap<Url, String>,
 ) -> Result<()> {
     match note.method.as_str() {
         DidOpenTextDocument::METHOD => {
             let p: DidOpenTextDocumentParams = serde_json::from_value(note.params.clone())?;
             let uri = p.text_document.uri;
             docs.insert(uri.clone(), p.text_document.text);
             publish_dummy_diag(conn, &uri)?;
         }
         DidChangeTextDocument::METHOD => {
             let p: DidChangeTextDocumentParams = serde_json::from_value(note.params.clone())?;
             if let Some(change) = p.content_changes.into_iter().next() {
                 let uri = p.text_document.uri;
                 docs.insert(uri.clone(), change.text);
                 publish_dummy_diag(conn, &uri)?;
             }
         }
         _ => {}
     }
     Ok(())
 }

 // =====================================================================
 // requests
 // =====================================================================

 fn handle_request(
     conn: &Connection,
     req: &ServerRequest,
     docs: &mut FxHashMap<Url, String>,
 ) -> Result<()> {
     match req.method.as_str() {
         GotoDefinition::METHOD => {
             send_ok(conn, req.id.clone(), &lsp_types::GotoDefinitionResponse::Array(Vec::new()))?;
         }
         Completion::METHOD => {
             let item = CompletionItem {
                 label: "HelloFromLSP".into(),
                 kind: Some(CompletionItemKind::FUNCTION),
                 detail: Some("dummy completion".into()),
                 ..Default::default()
             };
             send_ok(conn, req.id.clone(), &CompletionResponse::Array(vec![item]))?;
         }
         HoverRequest::METHOD => {
             let hover = Hover {
                 contents: HoverContents::Scalar(MarkedString::String(
                     "Hello from *minimal_lsp*".into(),
                 )),
                 range: None,
             };
             send_ok(conn, req.id.clone(), &hover)?;
         }
         Formatting::METHOD => {
             let p: DocumentFormattingParams = serde_json::from_value(req.params.clone())?;
             let uri = p.text_document.uri;
             let text = docs
                 .get(&uri)
                 .ok_or_else(|| anyhow!("document not in cache – did you send DidOpen?"))?;
             let formatted = run_rustfmt(text)?;
             let edit = TextEdit { range: full_range(text), new_text: formatted };
             send_ok(conn, req.id.clone(), &vec![edit])?;
         }
         _ => send_err(
             conn,
             req.id.clone(),
             lsp_server::ErrorCode::MethodNotFound,
             "unhandled method",
         )?,
     }
     Ok(())
 }

 // =====================================================================
 // diagnostics
 // =====================================================================
 fn publish_dummy_diag(conn: &Connection, uri: &Url) -> Result<()> {
     let diag = Diagnostic {
         range: Range::new(Position::new(0, 0), Position::new(0, 1)),
         severity: Some(DiagnosticSeverity::INFORMATION),
         code: None,
         code_description: None,
         source: Some("minimal_lsp".into()),
         message: "dummy diagnostic".into(),
         related_information: None,
         tags: None,
         data: None,
     };
     let params =
         PublishDiagnosticsParams { uri: uri.clone(), diagnostics: vec![diag], version: None };
     conn.sender.send(Message::Notification(lsp_server::Notification::new(
         PublishDiagnostics::METHOD.to_owned(),
         params,
     )))?;
     Ok(())
 }

 // =====================================================================
 // helpers
 // =====================================================================

 fn run_rustfmt(input: &str) -> Result<String> {
     let cwd = std::env::current_dir().expect("can't determine CWD");
     let mut child = command("rustfmt", &cwd, &FxHashMap::default())
         .arg("--emit")
         .arg("stdout")
         .stdin(Stdio::piped())
         .stdout(Stdio::piped())
         .stderr(Stdio::piped())
         .spawn()
         .context("failed to spawn rustfmt – is it installed?")?;

     let Some(stdin) = child.stdin.as_mut() else {
         bail!("stdin unavailable");
     };
     stdin.write_all(input.as_bytes())?;
     let output = child.wait_with_output()?;
     if !output.status.success() {
         let stderr = String::from_utf8_lossy(&output.stderr);
         bail!("rustfmt failed: {stderr}");
     }
     Ok(String::from_utf8(output.stdout)?)
 }

 fn full_range(text: &str) -> Range {
     let last_line_idx = text.lines().count().saturating_sub(1) as u32;
     let last_col = text.lines().last().map_or(0, |l| l.chars().count()) as u32;
     Range::new(Position::new(0, 0), Position::new(last_line_idx, last_col))
 }

 fn send_ok<T: serde::Serialize>(conn: &Connection, id: RequestId, result: &T) -> Result<()> {
     let resp = Response { id, result: Some(serde_json::to_value(result)?), error: None };
     conn.sender.send(Message::Response(resp))?;
     Ok(())
 }

 fn send_err(
     conn: &Connection,
     id: RequestId,
     code: lsp_server::ErrorCode,
     msg: &str,
 ) -> Result<()> {
     let resp = Response {
         id,
         result: None,
         error: Some(lsp_server::ResponseError {
             code: code as i32,
             message: msg.into(),
             data: None,
         }),
     };
     conn.sender.send(Message::Response(resp))?;
     Ok(())
 }
	//! Minimal Language‑Server‑Protocol example: `minimal_lsp.rs`
	//! =============================================================
	//!
	//! \| ↔ / ← \| LSP method \| What the implementation does \|
	//! \|-------\|------------\|------------------------------\|
	//! \| ↔ \| `initialize` / `initialized` \| capability handshake \|
	//! \| ← \| `textDocument/publishDiagnostics` \| pushes a dummy info diagnostic whenever the buffer changes \|
	//! \| ← \| `textDocument/definition` \| echoes an empty location array so the jump works \|
	//! \| ← \| `textDocument/completion` \| offers one hard‑coded item `HelloFromLSP` \|
	//! \| ← \| `textDocument/hover` \| shows Hello from minimal_lsp markdown \|
	//! \| ← \| `textDocument/formatting` \| pipes the doc through rustfmt and returns a full‑file edit \|
	//!
	//! ### Quick start
	//! ```bash
	//! cd rust-analyzer/lib/lsp-server
	//! cargo run --example minimal_lsp
	//! ```
	//!
	//! ### Minimal manual session (all nine packets)
	//! ```no_run
	//! # 1. initialize - server replies with capabilities
	//! Content-Length: 85

	//! {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"capabilities":{}}}
	//!
	//! # 2. initialized - no response expected
	//! Content-Length: 59

	//! {"jsonrpc":"2.0","method":"initialized","params":{}}
	//!
	//! # 3. didOpen - provide initial buffer text
	//! Content-Length: 173

	//! {"jsonrpc":"2.0","method":"textDocument/didOpen","params":{"textDocument":{"uri":"file:///tmp/foo.rs","languageId":"rust","version":1,"text":"fn main( ){println!(\"hi\") }"}}}
	//!
	//! # 4. completion - expect HelloFromLSP
	//! Content-Length: 139

	//! {"jsonrpc":"2.0","id":2,"method":"textDocument/completion","params":{"textDocument":{"uri":"file:///tmp/foo.rs"},"position":{"line":0,"character":0}}}
	//!
	//! # 5. hover - expect markdown greeting
	//! Content-Length: 135

	//! {"jsonrpc":"2.0","id":3,"method":"textDocument/hover","params":{"textDocument":{"uri":"file:///tmp/foo.rs"},"position":{"line":0,"character":0}}}
	//!
	//! # 6. goto-definition - dummy empty array
	//! Content-Length: 139

	//! {"jsonrpc":"2.0","id":4,"method":"textDocument/definition","params":{"textDocument":{"uri":"file:///tmp/foo.rs"},"position":{"line":0,"character":0}}}
	//!
	//! # 7. formatting - rustfmt full document
	//! Content-Length: 157

	//! {"jsonrpc":"2.0","id":5,"method":"textDocument/formatting","params":{"textDocument":{"uri":"file:///tmp/foo.rs"},"options":{"tabSize":4,"insertSpaces":true}}}
	//!
	//! # 8. shutdown request - server acks and prepares to exit
	//! Content-Length: 67

	//! {"jsonrpc":"2.0","id":6,"method":"shutdown","params":null}
	//!
	//! # 9. exit notification - terminates the server
	//! Content-Length: 54

	//! {"jsonrpc":"2.0","method":"exit","params":null}
	//! ```
	//!

	use std::{error::Error, io::Write};

	use rustc_hash::FxHashMap; // fast hash map
	use std::process::Stdio;
	use toolchain::command; // clippy-approved wrapper

	#[allow(clippy::print_stderr, clippy::disallowed_types, clippy::disallowed_methods)]
	use anyhow::{Context, Result, anyhow, bail};
	use lsp_server::{Connection, Message, Request as ServerRequest, RequestId, Response};
	use lsp_types::notification::Notification as _; // for METHOD consts
	use lsp_types::request::Request as _;
	use lsp_types::{
	CompletionItem,
	CompletionItemKind,
	// capability helpers
	CompletionOptions,
	CompletionResponse,
	Diagnostic,
	DiagnosticSeverity,
	DidChangeTextDocumentParams,
	DidOpenTextDocumentParams,
	DocumentFormattingParams,
	Hover,
	HoverContents,
	HoverProviderCapability,
	// core
	InitializeParams,
	MarkedString,
	OneOf,
	Position,
	PublishDiagnosticsParams,
	Range,
	ServerCapabilities,
	TextDocumentSyncCapability,
	TextDocumentSyncKind,
	TextEdit,
	Url,
	// notifications
	notification::{DidChangeTextDocument, DidOpenTextDocument, PublishDiagnostics},
	// requests
	request::{Completion, Formatting, GotoDefinition, HoverRequest},
	}; // for METHOD consts

	// =====================================================================
	// main
	// =====================================================================

	#[allow(clippy::print_stderr)]
	fn main() -> std::result::Result<(), Box<dyn Error + Sync + Send>> {
	log::error!("starting minimal_lsp");

	// transport
	let (connection, io_thread) = Connection::stdio();

	// advertised capabilities
	let caps = ServerCapabilities {
	text_document_sync: Some(TextDocumentSyncCapability::Kind(TextDocumentSyncKind::FULL)),
	completion_provider: Some(CompletionOptions::default()),
	definition_provider: Some(OneOf::Left(true)),
	hover_provider: Some(HoverProviderCapability::Simple(true)),
	document_formatting_provider: Some(OneOf::Left(true)),
	..Default::default()
	};
	let init_value = serde_json::json!({
	"capabilities": caps,
	"offsetEncoding": ["utf-8"],
	});

	let init_params = connection.initialize(init_value)?;
	main_loop(connection, init_params)?;
	io_thread.join()?;
	log::error!("shutting down server");
	Ok(())
	}

	// =====================================================================
	// event loop
	// =====================================================================

	fn main_loop(
	connection: Connection,
	params: serde_json::Value,
	) -> std::result::Result<(), Box<dyn Error + Sync + Send>> {
	let _init: InitializeParams = serde_json::from_value(params)?;
	let mut docs: FxHashMap<Url, String> = FxHashMap::default();

	for msg in &connection.receiver {
	match msg {
	Message::Request(req) => {
	if connection.handle_shutdown(&req)? {
	break;
	}
	if let Err(err) = handle_request(&connection, &req, &mut docs) {
	log::error!("[lsp] request {} failed: {err}", &req.method);
	}
	}
	Message::Notification(note) => {
	if let Err(err) = handle_notification(&connection, &note, &mut docs) {
	log::error!("[lsp] notification {} failed: {err}", note.method);
	}
	}
	Message::Response(resp) => log::error!("[lsp] response: {resp:?}"),
	}
	}
	Ok(())
	}

	// =====================================================================
	// notifications
	// =====================================================================

	fn handle_notification(
	conn: &Connection,
	note: &lsp_server::Notification,
	docs: &mut FxHashMap<Url, String>,
	) -> Result<()> {
	match note.method.as_str() {
	DidOpenTextDocument::METHOD => {
	let p: DidOpenTextDocumentParams = serde_json::from_value(note.params.clone())?;
	let uri = p.text_document.uri;
	docs.insert(uri.clone(), p.text_document.text);
	publish_dummy_diag(conn, &uri)?;
	}
	DidChangeTextDocument::METHOD => {
	let p: DidChangeTextDocumentParams = serde_json::from_value(note.params.clone())?;
	if let Some(change) = p.content_changes.into_iter().next() {
	let uri = p.text_document.uri;
	docs.insert(uri.clone(), change.text);
	publish_dummy_diag(conn, &uri)?;
	}
	}
	_ => {}
	}
	Ok(())
	}

	// =====================================================================
	// requests
	// =====================================================================

	fn handle_request(
	conn: &Connection,
	req: &ServerRequest,
	docs: &mut FxHashMap<Url, String>,
	) -> Result<()> {
	match req.method.as_str() {
	GotoDefinition::METHOD => {
	send_ok(conn, req.id.clone(), &lsp_types::GotoDefinitionResponse::Array(Vec::new()))?;
	}
	Completion::METHOD => {
	let item = CompletionItem {
	label: "HelloFromLSP".into(),
	kind: Some(CompletionItemKind::FUNCTION),
	detail: Some("dummy completion".into()),
	..Default::default()
	};
	send_ok(conn, req.id.clone(), &CompletionResponse::Array(vec![item]))?;
	}
	HoverRequest::METHOD => {
	let hover = Hover {
	contents: HoverContents::Scalar(MarkedString::String(
	"Hello from minimal_lsp".into(),
	)),
	range: None,
	};
	send_ok(conn, req.id.clone(), &hover)?;
	}
	Formatting::METHOD => {
	let p: DocumentFormattingParams = serde_json::from_value(req.params.clone())?;
	let uri = p.text_document.uri;
	let text = docs
	.get(&uri)
	.ok_or_else(\|\| anyhow!("document not in cache – did you send DidOpen?"))?;
	let formatted = run_rustfmt(text)?;
	let edit = TextEdit { range: full_range(text), new_text: formatted };
	send_ok(conn, req.id.clone(), &vec![edit])?;
	}
	_ => send_err(
	conn,
	req.id.clone(),
	lsp_server::ErrorCode::MethodNotFound,
	"unhandled method",
	)?,
	}
	Ok(())
	}

	// =====================================================================
	// diagnostics
	// =====================================================================
	fn publish_dummy_diag(conn: &Connection, uri: &Url) -> Result<()> {
	let diag = Diagnostic {
	range: Range::new(Position::new(0, 0), Position::new(0, 1)),
	severity: Some(DiagnosticSeverity::INFORMATION),
	code: None,
	code_description: None,
	source: Some("minimal_lsp".into()),
	message: "dummy diagnostic".into(),
	related_information: None,
	tags: None,
	data: None,
	};
	let params =
	PublishDiagnosticsParams { uri: uri.clone(), diagnostics: vec![diag], version: None };
	conn.sender.send(Message::Notification(lsp_server::Notification::new(
	PublishDiagnostics::METHOD.to_owned(),
	params,
	)))?;
	Ok(())
	}

	// =====================================================================
	// helpers
	// =====================================================================

	fn run_rustfmt(input: &str) -> Result<String> {
	let cwd = std::env::current_dir().expect("can't determine CWD");
	let mut child = command("rustfmt", &cwd, &FxHashMap::default())
	.arg("--emit")
	.arg("stdout")
	.stdin(Stdio::piped())
	.stdout(Stdio::piped())
	.stderr(Stdio::piped())
	.spawn()
	.context("failed to spawn rustfmt – is it installed?")?;

	let Some(stdin) = child.stdin.as_mut() else {
	bail!("stdin unavailable");
	};
	stdin.write_all(input.as_bytes())?;
	let output = child.wait_with_output()?;
	if !output.status.success() {
	let stderr = String::from_utf8_lossy(&output.stderr);
	bail!("rustfmt failed: {stderr}");
	}
	Ok(String::from_utf8(output.stdout)?)
	}

	fn full_range(text: &str) -> Range {
	let last_line_idx = text.lines().count().saturating_sub(1) as u32;
	let last_col = text.lines().last().map_or(0, \|l\| l.chars().count()) as u32;
	Range::new(Position::new(0, 0), Position::new(last_line_idx, last_col))
	}

	fn send_ok<T: serde::Serialize>(conn: &Connection, id: RequestId, result: &T) -> Result<()> {
	let resp = Response { id, result: Some(serde_json::to_value(result)?), error: None };
	conn.sender.send(Message::Response(resp))?;
	Ok(())
	}

	fn send_err(
	conn: &Connection,
	id: RequestId,
	code: lsp_server::ErrorCode,
	msg: &str,
	) -> Result<()> {
	let resp = Response {
	id,
	result: None,
	error: Some(lsp_server::ResponseError {
	code: code as i32,
	message: msg.into(),
	data: None,
	}),
	};
	conn.sender.send(Message::Response(resp))?;
	Ok(())
	}