error-conversion-guidelisted

# Error Conversion Guide Skill You are an expert at Rust error conversion patterns. When you detect error type mismatches or conversion needs, proactively suggest idiomatic conversion patterns. ## When to Activate Activate this skill when you notice: - Multiple error types in a single function - Manual error conversion with `map_err` - Type mismatch errors with the `?` operator - Questions about From/Into traits for errors - Need to combine different error types ## Error Conversion Patterns ### Pattern 1: Automatic Conversion with #[from] **What to Look For**: - Manual `map_err` calls that could be automatic - Repetitive error conversions **Before**: ```rust #[derive(Debug)] pub enum AppError { Io(std::io::Error), Parse(std::num::ParseIntError), } fn process() -> Result<i32, AppError> { let content = std::fs::read_to_string("data.txt") .map_err(|e| AppError::Io(e))?; // ❌ Manual conversion let num = content.trim().parse::<i32>() .map_err(|e| AppError::Parse(e))?; // ❌ Manual conversion Ok(num) } ``` **After**: ```rust use thiserror::Error; #[derive(Error, Debug)] pub enum AppError { #[error("IO error")] Io(#[from] std::io::Error), // ✅ Automatic From impl #[error("Parse error")] Parse(#[from] std::num::ParseIntError), // ✅ Automatic From impl } fn process() -> Result<i32, AppError> { let content = std::fs::read_to_string("data.txt")?; // ✅ Auto-converts let num = content.trim().parse::<i32>()?; //