Rust Coding Conventions

Rust Coding Conventions

General Principles

• Follow standard Rust conventions (use rustfmt and clippy)
• Use idiomatic Rust patterns throughout
• Prefer Result<T, E> for error handling over panics
• Apply RAII principles through Rust's ownership system
• Use const-correctness via immutable references (&)
• Write self-documenting code with clear naming and structure
• Leverage the type system for compile-time safety
• Keep functions focused and modular
• DRY (Don't Repeat Yourself): Extract shared logic into functions, traits, or structs. When the same pattern appears in 2+ places, factor it out. Use parameter structs (e.g. UpdateOptions) to aggregate related arguments rather than passing many individual parameters. Prefer a single source of truth for data.

Error Handling

• Use Result<T, E> for all fallible operations

• Use anyhow crate for error handling; re-export from lib.rs:

  pub use anyhow::Result;
  

• Use anyhow!() macro for constructing errors:

  Err(anyhow!("Config file not found"))
  Err(anyhow!("Failed to download {}: {}", url, e))
  

• Use ? operator for error propagation

• Avoid .unwrap() in library code; only use in application entry points after proper error handling

• Use .ok_or_else() or .ok_or() to convert Option to Result with meaningful error messages

• Never panic in library code unless documenting preconditions with #[panic] doc comments

• Use the require! macro for precondition checks with early return:

  require!(config_file.exists() == true, Err(anyhow!("Config not found")));
  require!(name.is_empty() == false, None);
  require!(count > 0, Ok(()));
  

  • Syntax: require!(condition, return_expression)
  • Returns the expression when the condition is false
  • Works with any return type: Result, Option, or bare values
  • Use require! only for precondition checks at the top of a function (before any real work), mimicking design-by-contract
  • Do NOT use require! for conditional logic deep inside function bodies; those should remain as regular if blocks

Comparison and Conditional Expressions

• Always use explicit boolean comparisons for clarity and consistency
• Use == true and == false instead of bare conditionals or negation
• Examples:
  • ✅ Correct: if condition == true, if value == false
  • ❌ Incorrect: if condition, if !value
• Exception: Direct variable tests in control flow are allowed when clearly intentional
• Apply to all boolean comparisons including Option and Result checks
• Use explicit comparisons with None: if option_value.is_none() == true or if option_value == None
• Allow clippy warnings for explicit boolean comparisons with project-level configuration

Loop Flow Control

• Avoid if condition { continue; } guards at the top of loop bodies; they add visual noise especially with AlwaysNextLine brace style

• Instead, combine guard conditions with the subsequent logic using &&, if/​else if/​else chains, or let-chains

• Examples:

  • ❌ Incorrect:

    for entry in &files
    {
        if entry.is_skippable() == true
        {
            continue;
        }
        if let Some(value) = entry.process()
        {
            handle(value);
        }
    }
    

  • ✅ Correct:

    for entry in &files
    {
        if entry.is_skippable() == false &&
            let Some(value) = entry.process()
        {
            handle(value);
        }
    }
    

• For multi-branch dispatch, use if/​else if/​else instead of continue to skip to the next branch

• Exception: continue inside match error arms (log-and-skip) is acceptable since it serves as early return from an error handler, not a guard

Module Organization

• Use module structure to organize code by functionality

• One public struct or major component per file

• Related utility functions in dedicated utils.rs

• Module declaration order in lib.rs:

  1. Private module declarations (mod)
  2. Public re-exports (pub use)
  3. Type aliases

• Example:

  mod template_manager;
  mod utils;
  
  pub use anyhow::Result;
  pub use template_manager::TemplateManager;
  pub use utils::copy_dir_all;
  

Functions and Methods

• Document all public APIs with doc comments (///)

• Use doc comment structure:

  • Brief one-line description (no explicit # Description header)
  • Longer explanation if needed (separated by blank line)
  • # Arguments section for parameters
  • # Returns section for return values (when non-obvious)
  • # Errors section for fallible functions
  • # Examples section when helpful
  • # Panics section if function can panic

• Example:

  /// Creates a new TemplateManager instance
  ///
  /// Initializes paths to local data and cache directories using the `dirs` crate.
  /// Templates are stored in the local data directory and backups in the cache directory.
  ///
  /// # Errors
  ///
  /// Returns an error if the local data directory cannot be determined
  pub fn new() -> Result<Self>
  

• Pass by reference (&) for complex types, by value for Copy types

• Use immutable references (&) unless mutation is required (&mut)

• Keep function signatures on one line when under max width (167 chars)

• Private helper functions should have single-line doc comments when logic is non-trivial

Structs and Types

• Use clear, descriptive names for all types
• Define fields in logical grouping order
• Document struct purpose and usage with doc comments
• Use #[derive] for common traits when appropriate
• Implement Default for structs with sensible defaults
• Group related structs together in the same file when tightly coupled
• Never wrap collection types in Option; use empty collections instead:
  • ❌ Option<Vec<T>>, Option<HashMap<K,V>> — creates redundant states (None vs empty)
  • ✅ Vec<T>, HashMap<K,V> — empty collection represents absence
  • For serde: use #[serde(default, skip_serializing_if = "Vec::is_empty")] or "HashMap::is_empty"
  • Option is appropriate for non-collection types where the default/​zero value differs from absence (e.g., Option<Config>)
• When exposing an internal Vec<T> via a getter, return &[T] (slice) not &Vec<T>

Naming Conventions

• Types (structs, enums, traits): Upper PascalCase (e.g., TemplateManager, FileMapping, Result)
• Functions/​methods: snake_case (e.g., download_file, create_backup, load_template_config)
• Variables and function parameters: snake_case (e.g., config_dir, source_path, file_name)
• Constants: UPPER_SNAKE_CASE (e.g., MAX_WIDTH, DEFAULT_TIMEOUT)
• Type parameters: Single uppercase letter or PascalCase (e.g., T, E, Error)
• Lifetimes: Short lowercase names (e.g., 'a, 'static)
• Module names: snake_case (e.g., template_manager, utils)

Enums and Pattern Matching

• Use descriptive variant names in PascalCase

• Derive common traits when appropriate

• Use #[derive(Debug)] for all types when possible for better error messages

• Use exhaustive pattern matching; avoid _ => catch-alls when possible

• Use if let for single-pattern matching

• Use match for multiple patterns or when you need exhaustiveness checking

• Use let...else for early returns with single pattern:

  let Some(value) = option else {
      return Err(anyhow!("Missing value"));
  };
  

CLI Design with clap

• Use clap's derive API for argument parsing

• Define main CLI struct with #[derive(Parser)]

• Use #[derive(Subcommand)] for command structure

• Add helpful descriptions with #[command] attributes

• Example:

  #[derive(Parser)]
  #[command(name = "vibe-check")]
  #[command(about = "A manager for coding agent instruction files", long_about = None)]
  struct Cli
  {
      #[command(subcommand)]
      command: Commands
  }
  

• Use clear, descriptive field names that match CLI conventions

• Provide defaults with #[arg(default_value = "...")]

• Add documentation comments to show in --help output

Formatting Configuration (.rustfmt.toml)

• Use project-specific rustfmt configuration for consistency
• Key formatting rules:
  • max_width = 167 - Allow longer lines for readability
  • brace_style = "AlwaysNextLine" - Opening braces on new lines
  • control_brace_style = "AlwaysNextLine" - Consistent brace placement
  • trailing_comma = "Never" - No trailing commas
  • edition = "2024" - Use latest Rust edition
  • tab_spaces = 4 - Standard indentation
  • imports_granularity = "Crate" - Group imports by crate
  • group_imports = "StdExternalCrate" - Organize imports logically
• Run cargo fmt before committing code
• Configure editor to format on save

Imports and Dependencies

• Group imports in order:

  1. Standard library (std::)
  2. External crates (alphabetically)
  3. Project modules (crate::)

• Use explicit imports over glob imports

• Example:

  use std::{
      fs,
      io::{self, Write},
      path::{Path, PathBuf}
  };
  
  use chrono::{DateTime, Utc};
  use owo_colors::OwoColorize;
  use serde::{Deserialize, Serialize};
  
  use crate::{Result, utils::copy_dir_all};
  

• Re-export commonly used items from lib.rs for convenience

Conditional Compilation and Features

• Use feature flags for optional functionality

• Document feature requirements in doc comments

• Use #[cfg(feature = "...")] for conditional code

• Specify features in Cargo.toml dependencies when needed:

  reqwest = { version = "0.12", features = ["blocking", "json"] }
  

Testing

• Write unit tests alongside implementation in the same file

• Use #[cfg(test)] module for tests

• Name test functions descriptively: test_<scenario>_<expected_outcome>

• Use assert!, assert_eq!, assert_ne! macros

• Test both success and error cases

• Example:

  #[cfg(test)]
  mod tests
  {
      use super::*;
  
      #[test]
      fn test_parse_github_url_valid()
      {
          // Test implementation
      }
  }
  

Comments and Documentation

• Use /// for public API documentation (appears in generated docs)

• Use //! for module-level documentation at file top

• Use // for implementation comments and explanations

• Document the "why" not the "what" in implementation comments

• Keep comments up-to-date with code changes

• Use full sentences with proper punctuation in doc comments

• Example:

  //! Template management functionality for vibe-check
  
  /// Creates a timestamped backup of a directory
  ///
  /// Backups are stored in the cache directory with timestamp: `backups/​YYYY-MM-DD_HH_MM_SS/`
  fn create_backup(&self, source_dir: &Path) -> Result<()>
  {
      // Skip backup if source doesn't exist
      if source_dir.exists() == false
      {
          return Ok(());
      }
      // ... rest of implementation
  }
  

Linting Configuration

• Allow specific clippy lints when project style differs from defaults

• Configure in Cargo.toml:

  [lints.clippy]
  bool_comparison = "allow"
  

• Can also use module-level attributes:

  #![allow(clippy::bool_comparison)]
  

• Document reasoning for lint exceptions

File Organization

• Entry point: src/​main.rs (minimal, delegates to library)

• Library API: src/​lib.rs (public interface)

• Implementation: Feature modules in src/

• Keep main.rs focused on CLI handling and error reporting

• Put business logic in library modules for reusability

• Example structure:

  src/
  ├── main.rs              # CLI entry point
  ├── lib.rs               # Public API
  ├── template_manager.rs  # Core functionality
  └── utils.rs             # Shared utilities
  

Best Practices

• Use std::env::current_dir() over hardcoding paths

• Use Path and PathBuf for filesystem paths

• Use Path::starts_with() for path prefix/​subpath checks; avoid string-based path comparison (e.g. path.starts_with("foo/")) to ensure cross-platform behavior (Windows uses \, Unix uses /)

• When resolving placeholders in paths (e.g. $workspace/​AGENTS.md), use Path::join() with the suffix instead of string replace; string replace can produce mixed separators on Windows

• Leverage std::io::Write trait for flushing output buffers

• Use owo-colors or similar crate for terminal output styling

• Use platform-appropriate paths via dirs crate (prefer over $HOME env var)

• Implement flush() when printing without newline for immediate output:

  print!("{} Processing... ", "→".blue());
  io::stdout().flush()?;
  

• Use early returns to reduce nesting depth

• Prefer iterators and functional patterns over loops when clear

Error Messages

• Use colored output for user-facing messages (owo-colors)

• Format: "{} {}", symbol.color(), message.color()

• Symbols: ✓ (success/​green), ✗ (error/​red), → (info/​blue), ! (warning/​yellow), ? (prompt/​yellow)

• Provide actionable error messages

• Include file paths and operation details in errors

• Example:

  println!("{} Creating backup in {}", "→".blue(), backup_dir.display().to_string().yellow());
  eprintln!("{} Failed to download {}: {}", "✗".red(), url, error.to_string().red());
  

Version and Edition

• Use Rust 2024 edition for latest language features

• Specify in Cargo.toml:

  [package]
  edition = "2024"
  

• Keep dependencies up-to-date but specify versions explicitly

• Use semantic versioning in package version

Code Review Checklist

• All public APIs have doc comments
• Error handling uses Result consistently
• No .unwrap() calls in library code
• Explicit boolean comparisons used throughout
• Code formatted with cargo fmt
• No clippy warnings (or explicitly allowed with reasoning)
• Tests pass with cargo test
• Code builds in both debug and release modes
• Imports organized and minimal
• Functions are focused and modular
• CRITICAL: Always verify documentation against actual implementation