Module :: error_tools

A unified error handling facade that provides a consistent interface for both typed and untyped error handling in Rust. error_tools acts as a standardized wrapper around the popular thiserror and anyhow crates, enabling you to write error-handling code once and use it consistently across different contexts.

Why error_tools?

When building Rust applications and libraries, you often face these error handling challenges:

• Library vs Application Choice: Libraries typically use thiserror for typed errors, while applications prefer anyhow for flexibility
• Inconsistent Error Patterns: Different crates in your dependency tree use different error handling approaches
• Dependency Fragmentation: Having both anyhow and thiserror as direct dependencies across multiple crates
• Context Switching: Different syntax and patterns for similar error handling tasks
• Integration Friction: Converting between different error types when bridging library and application code

error_tools solves these problems by providing:

• 🎯 Unified Interface: Single import pattern for both typed and untyped errors
• 📦 Dependency Facade: Centralized re-export of anyhow and thiserror functionality
• 🔧 Enhanced Utilities: Additional error handling utilities like ErrWith trait
• 🏗️ Consistent Patterns: Standardized error handling across the entire wTools ecosystem
• 🚀 Easy Migration: Drop-in replacement for existing anyhow/thiserror usage
• 🛡️ no_std Support: Works in no_std environments when needed

Quick Start

Installation

cargo add error_tools

Basic Usage

Choose your approach based on your needs:

// For applications - flexible, untyped errors (anyhow-style)
use error_tools::untyped::*;

// For libraries - structured, typed errors (thiserror-style)  
use error_tools::typed::*;
use error_tools::dependency::thiserror;

// For convenience - includes both
use error_tools::prelude::*;

Core Concepts

1. Untyped Errors (Application-Focused)

Perfect for applications where you need flexible error handling without defining custom error types for every possible failure. This is a direct facade over anyhow.

Key Features:

• Dynamic error handling with context
• Easy error chaining and reporting
• Rich context information
• Perfect for rapid prototyping and applications

use error_tools::untyped::{ Result, format_err };

fn get_message() -> Result< &'static str >
{
  Ok( "Hello, world!" )
  // Err( format_err!( "An unexpected error!" ) )
}

fn main()
{
  match get_message()
  {
    Ok( msg ) => println!( "Success: {}", msg ),
    Err( e ) => println!( "Error: {:?}", e ),
  }
}

Run this example:

cargo run --example error_tools_trivial

2. Working with Context

Adding context to errors helps with debugging and user experience:

use error_tools::untyped::{ Result, Context, format_err };

fn read_and_process_file( path : &str ) -> Result< String >
{
  // Simulate file reading for demonstration  
  let content = if path == "test.txt" { "hello world" } else { "" };
  
  if content.is_empty()
  {
    return Err( format_err!( "File is empty or not found: {}", path ) );
  }

  Ok( content.to_uppercase() )
}

fn main()
{
  match read_and_process_file( "test.txt" )
  {
    Ok( content ) => println!( "Processed: {}", content ),
    Err( e ) => println!( "Error: {}", e ),
  }
}

See the full runnable example in examples/replace_anyhow.rs.

3. Typed Errors (Library-Focused)

Ideal for libraries where you want to provide a clear, structured contract for possible errors. This is a facade over thiserror.

Key Features:

• Structured error types with derive macros
• Clear error hierarchies
• Compile-time error checking
• Better API boundaries for library consumers

use error_tools::typed::Error;
use error_tools::dependency::thiserror;

#[ derive( Debug, Error ) ]
pub enum DataError
{
  #[ error( "I/O error for file: {file}" ) ]
  Io { file : String },
  #[ error( "Parsing error: {0}" ) ]
  Parse( String ),
}

fn process_data( file_name : &str, content : &str ) -> Result< i32, DataError >
{
  if content.is_empty()
  {
    return Err( DataError::Io { file : file_name.to_string() } );
  }

  content.trim().parse::< i32 >()
    .map_err( | _ | DataError::Parse( "Could not parse content as integer".into() ) )
}

fn main()
{
  match process_data( "data.txt", "123" )
  {
    Ok( num ) => println!( "Parsed number: {}", num ),
    Err( e ) => println!( "Error: {}", e ),
  }
  
  // Example with error
  match process_data( "invalid.txt", "abc" )
  {
    Ok( _ ) => (),
    Err( e ) => println!( "Expected error: {}", e ),
  }
}

See the full runnable example in examples/replace_thiserror.rs.

4. Enhanced Error Context with ErrWith

The ErrWith trait provides additional utilities for adding context to errors:

use error_tools::{ ErrWith };

fn process_user_data( user_id : u32, data : &str ) -> Result< String, ( String, Box< dyn std::error::Error > ) >
{
  // Add context using closures for lazy evaluation
  let parsed_data = data.parse::< i32 >()
    .err_with( || format!( "Failed to parse data for user {}", user_id ) )?;

  // Add context using references for simple messages  
  let processed = perform_calculation( parsed_data )
    .err_with_report( &format!( "Calculation failed for user {}", user_id ) )?;

  Ok( format!( "Processed: {}", processed ) )
}

fn perform_calculation( input : i32 ) -> std::result::Result< i32, &'static str >
{
  if input < 0
  {
    Err( "Negative numbers not supported" )
  }
  else
  {
    Ok( input * 2 )
  }
}

fn main()
{
  match process_user_data( 123, "42" )
  {
    Ok( result ) => println!( "Success: {}", result ),
    Err( ( report, err ) ) => println!( "Error: {} - {:?}", report, err ),
  }
}

See the full runnable example in examples/err_with_example.rs.

5. Debug Assertions

Additional debugging utilities for development:

use error_tools::{ debug_assert_id, debug_assert_ni };

fn validate_data( expected : &str, actual : &str )
{
  // Only active in debug builds
  debug_assert_id!( expected, actual, "Data validation failed" );
  
  // Negative assertion
  debug_assert_ni!( expected, "", "Expected data should not be empty" );
}

fn main()
{
  validate_data( "test", "test" );
  println!( "Debug assertions passed!" );
}

Examples

Basic Error Handling

use error_tools::untyped::Result;

fn might_fail( should_fail : bool ) -> Result< String >
{
  if should_fail
  {
    Err( error_tools::untyped::format_err!( "Something went wrong" ) )
  }
  else
  {
    Ok( "Success!".to_string() )
  }
}

fn main()
{
  match might_fail( false )
  {
    Ok( msg ) => println!( "Result: {}", msg ),
    Err( e ) => println!( "Error: {}", e ),
  }
}

Using Both Typed and Untyped Errors

use error_tools::prelude::*;
use error_tools::dependency::thiserror;

// Typed error for library API
#[ derive( Debug, Error ) ]
pub enum ConfigError
{
  #[ error( "Configuration file not found" ) ]
  NotFound,
  #[ error( "Invalid format: {0}" ) ]
  InvalidFormat( String ),
}

// Function returning typed error
fn load_config_typed() -> Result< String, ConfigError >
{
  Err( ConfigError::NotFound )
}

// Function returning untyped error
fn load_config_untyped() -> error_tools::untyped::Result< String >
{
  Err( error_tools::untyped::format_err!( "Configuration loading failed" ) )
}

fn main()
{
  // Handle typed error
  if let Err( e ) = load_config_typed()
  {
    println!( "Typed error: {}", e );
  }

  // Handle untyped error  
  if let Err( e ) = load_config_untyped()
  {
    println!( "Untyped error: {}", e );
  }
}

Feature Flags

error_tools supports granular feature control:

[dependencies]
error_tools = { version = "0.26", features = [ "error_typed" ] }  # Only typed errors
# or
error_tools = { version = "0.26", features = [ "error_untyped" ] }  # Only untyped errors  
# or
error_tools = { version = "0.26" }  # Both (default)

Available Features:

• default - Enables both error_typed and error_untyped
• error_typed - Enables thiserror integration for structured errors
• error_untyped - Enables anyhow integration for flexible errors
• no_std - Enables no_std support
• use_alloc - Enables allocation support in no_std environments

Migration Guide

From anyhow

Replace your anyhow imports with error_tools::untyped:

// Before
// use anyhow::{ Result, Context, bail, format_err };

// After  
use error_tools::untyped::{ Result, Context, bail, format_err };

fn main() 
{
    println!("Migration complete - same API, different import!");
}

Everything else stays the same!

From thiserror

Add the explicit thiserror import and use error_tools::typed:

// Before
// use thiserror::Error;

// After
use error_tools::typed::Error;
use error_tools::dependency::thiserror;  // Required for derive macros

fn main() 
{
    println!("Migration complete - same derive macros, unified import!");
}

The derive macros work identically.

Complete Examples

Explore these runnable examples in the repository:

# Basic usage patterns
cargo run --example error_tools_trivial

# Migration from anyhow
cargo run --example replace_anyhow

# Migration from thiserror  
cargo run --example replace_thiserror

# Using the ErrWith trait
cargo run --example err_with_example

Best Practices

1. Choose the Right Error Style

• Applications: Use untyped errors for flexibility and rapid development
• Libraries: Use typed errors for clear API contracts and better user experience
• Mixed Projects: Use both as appropriate - they interoperate well

2. Error Context

Always provide meaningful context:

use error_tools::untyped::{ Result, Context, format_err };

fn process_user_data( user_id : u32 ) -> Result< String >
{
  // Good - specific context
  let _result = simulate_operation()
    .context( format!( "Failed to process user {} data", user_id ) )?;

  // Less helpful - generic context  
  let _other = simulate_operation()
    .context( "An error occurred" )?;

  Ok( "Success".to_string() )
}

fn simulate_operation() -> Result< String >
{
  Ok( "data".to_string() )
}

fn main()
{
  match process_user_data( 123 )
  {
    Ok( result ) => println!( "Result: {}", result ),
    Err( e ) => println!( "Error: {}", e ),
  }
}

3. Error Hierarchies

For libraries, design clear error hierarchies:

use error_tools::typed::Error;
use error_tools::dependency::thiserror;

#[ derive( Debug, Error ) ]
pub enum LibraryError
{
  #[ error( "Configuration error: {0}" ) ]
  Config( #[from] ConfigError ),
  
  #[ error( "Network error: {0}" ) ]
  Network( #[from] NetworkError ),
  
  #[ error( "Database error: {0}" ) ]
  Database( #[from] DatabaseError ),
}

// Define the individual error types
#[ derive( Debug, Error ) ]
pub enum ConfigError
{
  #[ error( "Config not found" ) ]
  NotFound,
}

#[ derive( Debug, Error ) ]  
pub enum NetworkError
{
  #[ error( "Connection failed" ) ]
  ConnectionFailed,
}

#[ derive( Debug, Error ) ]
pub enum DatabaseError
{
  #[ error( "Query failed" ) ]
  QueryFailed,
}

fn main()
{
  let config_err = LibraryError::Config( ConfigError::NotFound );
  println!( "Error hierarchy example: {}", config_err );
}

4. Dependency Access

When you need direct access to the underlying crates:

// Access the underlying crates if needed
// use error_tools::dependency::{ anyhow, thiserror };

// Or via the specific modules
use error_tools::untyped;  // Re-exports anyhow
use error_tools::typed;    // Re-exports thiserror

fn main()
{
    println!("Direct access to underlying crates available via dependency module");
}

Integration with wTools Ecosystem

error_tools is designed to work seamlessly with other wTools crates:

• Consistent Error Handling: All wTools crates use error_tools for unified error patterns
• Cross-Crate Compatibility: Errors from different wTools crates integrate naturally
• Standardized Debugging: Common debugging utilities across the ecosystem

To add to your project

cargo add error_tools

Try out from the repository

git clone https://github.com/Wandalen/wTools
cd wTools
cargo run --example error_tools_trivial
# Or try the specific examples
cargo run --example replace_anyhow
cargo run --example replace_thiserror
cargo run --example err_with_example