我将根据您提供的内容，整理关于codespan-lsp的完整示例demo。首先展示内容中已有的示例，然后提供一个更完整的实现。

已有示例代码回顾

基本语言服务器示例

use codespan_lsp::{
    server::{LanguageServer, Server},
    PositionEncoding,
};
use tower::Service;

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    let (service, messages) = LanguageServer::new(|client| Server {
        client,
        position_encoding: PositionEncoding::Utf8,
    });

    let stdin = tokio::io::stdin();
    let stdout = tokio::io::stdout();

    codespan_lsp::stdio::run(&mut service, &messages, stdin, stdout).await?;

    Ok(())
}

Rust语法检查器示例

use codespan_lsp::{
    server::{LanguageServer, Server},
    lsp_types::{
        Url, Diagnostic, DiagnosticSeverity, Position, Range,
        PublishDiagnosticsParams, DidOpenTextDocumentParams,
    },
};
use tower::Service;

struct RustLinter {
    documents: std::collections::HashMap<Url, String>,
}

impl Server for RustLinter {
    fn on_open_text_document(
        &mut self,
        params: DidOpenTextDocumentParams,
    ) -> Option<codespan_lsp::server::Request> {
        let uri = params.text_document.uri;
        let text = params.text_document.text;
        self.documents.insert(uri.clone(), text.clone());
        
        let diagnostics = if !text.contains("fn main()") {
            vec![Diagnostic {
                range: Range {
                    start: Position { line: 0, character: 0 },
                    end: Position { line: 0, character: 0 },
                },
                severity: Some(DiagnosticSeverity::Warning),
                message: "Rust file should contain a main function".to_string(),
                ..Default::default()
            }]
        } else {
            vec![]
        };
        
        Some(codespan_lsp::server::Request::PublishDiagnostics(
            PublishDiagnosticsParams {
                uri,
                diagnostics,
                version: None,
            }
        ))
    }
}

完整示例：增强型Rust语言服务器

下面是一个更完整的Rust语言服务器实现，包含语法检查、错误诊断和简单的代码补全功能：

use codespan_lsp::{
    server::{LanguageServer, Server},
    lsp_types::{
        Url, Diagnostic, DiagnosticSeverity, Position, Range,
        PublishDiagnosticsParams, DidOpenTextDocumentParams,
        DidChangeTextDocumentParams, CompletionParams, CompletionItem,
        CompletionResponse, InitializeParams,
    },
    PositionEncoding,
};
use tower::Service;
use std::collections::HashMap;

struct EnhancedRustServer {
    documents: HashMap<Url, String>,
    position_encoding: PositionEncoding,
}

impl Server for EnhancedRustServer {
    fn initialize(&mut self, params: InitializeParams) -> Option<codespan_lsp::server::Request> {
        // 设置位置编码
        self.position_encoding = params.capabilities.position_encoding
            .unwrap_or(PositionEncoding::Utf8);
        None
    }

    fn on_open_text_document(
        &mut self,
        params: DidOpenTextDocumentParams,
    ) -> Option<codespan_lsp::server::Request> {
        let uri = params.text_document.uri;
        let text = params.text_document.text;
        self.documents.insert(uri.clone(), text.clone());
        
        // 检查基本的Rust语法
        let mut diagnostics = Vec::new();
        
        if !text.contains("fn main()") {
            diagnostics.push(Diagnostic {
                range: Range {
                    start: Position { line: 0, character: 0 },
                    end: Position { line: 0, character: 0 },
                },
                severity: Some(DiagnosticSeverity::Warning),
                message: "Rust文件应该包含main函数".to_string(),
                ..Default::default()
            });
        }
        
        // 检查常见的语法错误
        if text.contains("let mut") && !text.contains("=") {
            diagnostics.push(Diagnostic {
                range: Range {
                    start: Position { line: 0, character: 0 },
                    end: Position { line: 0, character: 0 },
                },
                severity: Some(DiagnosticSeverity::Error),
                message: "可变绑定必须初始化".to_string(),
                ..Default::default()
            });
        }

        Some(codespan_lsp::server::Request::PublishDiagnostics(
            PublishDiagnosticsParams {
                uri,
                diagnostics,
                version: None,
            }
        ))
    }

    fn on_change_text_document(
        &mut self,
        params: DidChangeTextDocumentParams,
    ) -> Option<codespan_lsp::server::Request> {
        let uri = params.text_document.uri;
        if let Some(text) = params.content_changes.into_iter().next() {
            self.documents.insert(uri.clone(), text.text);
        }
        None
    }

    fn on_completion(
        &mut self,
        _params: CompletionParams,
    ) -> Option<codespan_lsp::server::Request> {
        // 提供简单的自动补全
        let items = vec![
            CompletionItem {
                label: "fn".to_string(),
                kind: Some(lsp_types::CompletionItemKind::KEYWORD),
                detail: Some("函数定义".to_string()),
                ..Default::default()
            },
            CompletionItem {
                label: "let".to_string(),
                kind: Some(lsp_types::CompletionItemKind::KEYWORD),
                detail: Some("变量绑定".to_string()),
                ..Default::default()
            },
            CompletionItem {
                label: "println!".to_string(),
                kind: Some(lsp_types::CompletionItemKind::FUNCTION),
                detail: Some("打印宏".to_string()),
                ..Default::default()
            },
        ];

        Some(codespan_lsp::server::Request::CompletionResponse(
            CompletionResponse::Array(items)
        ))
    }
}

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    // 创建语言服务器实例
    let (mut service, messages) = LanguageServer::new(|client| EnhancedRustServer {
        documents: HashMap::new(),
        position_encoding: PositionEncoding::Utf8,
    });

    // 运行标准IO服务
    let stdin = tokio::io::stdin();
    let stdout = tokio::io::stdout();
    
    codespan_lsp::stdio::run(&mut service, &messages, stdin, stdout).await?;
    
    Ok(())
}

关键功能说明

1. 初始化处理：通过initialize方法设置位置编码
2. 文档管理：使用HashMap跟踪打开的文档内容
3. 语法检查：
   • 检查是否包含main函数
   • 验证可变绑定是否初始化
4. 变更通知：处理文档内容变更
5. 代码补全：提供基本的Rust关键字和宏补全

扩展建议

1. 集成codespan诊断：可以结合codespan库提供更精确的错误定位
2. 添加更多分析功能：如类型检查、借用检查等
3. 支持更多LSP特性：如代码格式化、重命名等

这个完整示例展示了如何使用codespan-lsp构建一个功能相对完整的Rust语言服务器，可以作为开发更复杂语言工具的基础。