clippy-advanced - Advanced Clippy Configuration

Advanced Clippy configuration for comprehensive Rust linting, including custom rules, lint categories, disallowed methods, and IDE integration.

Installation

# Clippy is included with rustup
rustup component add clippy

# Verify installation
cargo clippy --version

# Update clippy with rust toolchain
rustup update

Basic Usage

# Run clippy on current project
cargo clippy

# Run on all targets (lib, bins, tests, examples, benches)
cargo clippy --all-targets

# Run with all features enabled
cargo clippy --all-features

# Run on workspace
cargo clippy --workspace --all-targets --all-features

# Show detailed lint explanations
cargo clippy -- -W clippy::all -A clippy::pedantic

# Treat warnings as errors
cargo clippy -- -D warnings

clippy.toml Configuration File

Create clippy.toml or .clippy.toml in project root:

# clippy.toml - Project-wide clippy configuration

# Enforce documentation for public items
# Warn if public items are missing documentation
missing-docs-in-crate-items = "warn"

# Cognitive complexity threshold
# Functions with complexity above this will trigger a warning
cognitive-complexity-threshold = 15

# Type complexity threshold
# Complex types will trigger a warning
type-complexity-threshold = 100

# Function length threshold
# Long functions will trigger a warning
too-many-lines-threshold = 100

# Too many arguments threshold
too-many-arguments-threshold = 5

# Vec box size threshold
# Large heap allocations in Vec will trigger a warning
vec-box-size-threshold = 4096

# Disallowed methods with custom messages
disallowed-methods = [
  { path = "std::env::var", reason = "Use std::env::var_os for better Unicode handling" },
  { path = "std::panic::catch_unwind", reason = "Prefer structured error handling" },
  { path = "std::process::exit", reason = "Use Result propagation instead" },
]

# Disallowed types
disallowed-types = [
  { path = "std::collections::HashMap", reason = "Use indexmap::IndexMap for deterministic iteration" },
  { path = "once_cell::sync::Lazy", reason = "Use std::sync::LazyLock (Rust 1.80+)" },
]

# Allowed identifiers (bypass naming lints)
allowed-idents-below-min-chars = ["i", "j", "x", "y", "id", "db"]

# Import granularity (prefer full paths)
# Options: "crate", "module", "item", "one"
imports-granularity = "module"

# Enforce module inception
# Warn about modules that only contain a single item
# which could be moved up to parent module
allow-module-inception = false

# Standard library imports style
# Options: "absolute", "module"
imports-prefer-module = true

# Single component path imports
# Warn about imports of single component paths
single-component-path-imports = "warn"

# Array size threshold for performance lints
# Large arrays passed by value will trigger a warning
array-size-threshold = 512

# String literal as bytes
# Prefer b"string" over "string".as_bytes()
# Options: "always", "never"
literal-representation = "always"

# Allowed scripts for confusable characters
# Prevent mixing similar-looking characters from different scripts
allowed-confusable-scripts = ["Latin", "Greek"]

# Semicolon consistency
# Options: "never", "always"
semicolon-if-nothing-returned = "always"

# Blacklist/whitelist naming
# Use inclusive terminology
disallowed-names = ["foo", "bar", "baz", "master", "slave", "whitelist", "blacklist"]

# Prefer module-level documentation
doc-markdown-inline-code = true

Lint Categories

All Available Categories

# Default lints (enabled by default)
cargo clippy -- -W clippy::all

# Pedantic lints (opinionated style)
cargo clippy -- -W clippy::pedantic

# Restriction lints (opt-in for specific constraints)
cargo clippy -- -W clippy::restriction

# Nursery lints (experimental, may have false positives)
cargo clippy -- -W clippy::nursery

# Cargo lints (Cargo.toml issues)
cargo clippy -- -W clippy::cargo

# Complexity lints (overly complex code)
cargo clippy -- -W clippy::complexity

# Correctness lints (likely bugs)
cargo clippy -- -W clippy::correctness

# Perf lints (performance issues)
cargo clippy -- -W clippy::perf

# Style lints (code style)
cargo clippy -- -W clippy::style

# Suspicious lints (code that looks wrong)
cargo clippy -- -W clippy::suspicious

Recommended Category Combination

# Cargo.toml
[workspace.lints.clippy]
# Deny correctness issues (likely bugs)
correctness = "deny"

# Warn on complexity
complexity = "warn"

# Warn on performance issues
perf = "warn"

# Warn on style issues
style = "warn"

# Warn on suspicious patterns
suspicious = "warn"

# Enable pedantic but allow some noisy lints
pedantic = "warn"
must_use_candidate = "allow"
missing_errors_doc = "allow"

# Enable some restriction lints selectively
clone_on_ref_ptr = "warn"
dbg_macro = "warn"
print_stdout = "warn"
todo = "warn"
unimplemented = "warn"

# Enable nursery lints (experimental)
use_self = "warn"

Cargo.toml Lint Configuration (Recommended)

# Cargo.toml - Modern workspace lint configuration (Rust 1.74+)
[workspace.lints.clippy]
# Correctness - deny bugs
correctness = { level = "deny", priority = -1 }

# Complexity
complexity = "warn"
cognitive_complexity = "warn"
too_many_arguments = "warn"
too_many_lines = "warn"
type_complexity = "warn"

# Performance
perf = "warn"
large_enum_variant = "warn"
large_stack_arrays = "warn"

# Style
style = "warn"
missing_docs_in_private_items = "warn"

# Pedantic (selective)
pedantic = "warn"
must_use_candidate = "allow"
missing_errors_doc = "allow"
missing_panics_doc = "allow"
module_name_repetitions = "allow"

# Restriction (opt-in)
clone_on_ref_ptr = "warn"
dbg_macro = "warn"
empty_drop = "warn"
exit = "warn"
expect_used = "warn"
filetype_is_file = "warn"
get_unwrap = "warn"
panic = "warn"
print_stderr = "warn"
print_stdout = "warn"
todo = "warn"
unimplemented = "warn"
unreachable = "warn"
unwrap_used = "warn"

# Nursery (experimental, may have false positives)
use_self = "warn"
useless_let_if_seq = "warn"

# Cargo
cargo = "warn"
multiple_crate_versions = "warn"

[workspace.lints.rust]
# Rust lints
missing_docs = "warn"
unsafe_code = "warn"

Allow and Deny Attributes

Function-level Overrides

// Allow specific lint for entire function
#[allow(clippy::too_many_arguments)]
fn complex_function(a: i32, b: i32, c: i32, d: i32, e: i32, f: i32) {
    // ...
}

// Deny specific lint
#[deny(clippy::unwrap_used)]
fn critical_function() -> Result<(), Error> {
    // This will error if unwrap() is used
    Ok(())
}

// Warn for specific lint
#[warn(clippy::print_stdout)]
fn debug_function() {
    println!("This will warn");
}

Module-level Configuration

// src/lib.rs or src/main.rs
#![warn(clippy::all)]
#![warn(clippy::pedantic)]
#![warn(clippy::nursery)]
#![deny(clippy::unwrap_used)]
#![deny(clippy::expect_used)]

// Allow specific lints
#![allow(clippy::module_name_repetitions)]
#![allow(clippy::must_use_candidate)]

// Individual module configuration
#[allow(clippy::pedantic)]
mod legacy_code {
    // Disable pedantic for this module
}

Inline Suppression

// Suppress for specific line
#[allow(clippy::cast_possible_truncation)]
let x = value as u8;

// Suppress for expression
let y = {
    #[allow(clippy::cast_sign_loss)]
    negative_value as u32
};

// Suppress for block
{
    #![allow(clippy::indexing_slicing)]
    let element = slice[index];
}

CI Integration

GitHub Actions - Strict Linting

name: Clippy

on: [push, pull_request]

env:
  CARGO_TERM_COLOR: always

jobs:
  clippy:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - uses: dtolnay/rust-toolchain@stable
        with:
          components: clippy

      - uses: Swatinem/rust-cache@v2

      - name: Run clippy
        run: |
          cargo clippy --workspace --all-targets --all-features -- -D warnings

      - name: Run clippy pedantic
        run: |
          cargo clippy --workspace --all-targets --all-features -- \
            -W clippy::pedantic \
            -W clippy::nursery \
            -D clippy::correctness

GitHub Actions - Reviewdog Integration

name: Clippy Review

on: [pull_request]

jobs:
  clippy-review:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - uses: dtolnay/rust-toolchain@stable
        with:
          components: clippy

      - uses: Swatinem/rust-cache@v2

      - uses: giraffate/clippy-action@v1
        with:
          reporter: 'github-pr-review'
          github_token: ${{ secrets.GITHUB_TOKEN }}
          clippy_flags: --all-targets --all-features

Pre-commit Hook

# .pre-commit-config.yaml
repos:
  - repo: local
    hooks:
      - id: cargo-clippy
        name: cargo clippy
        entry: cargo clippy
        args: ['--all-targets', '--all-features', '--', '-D', 'warnings']
        language: system
        pass_filenames: false
        files: \.rs$

rust-analyzer Integration

Configure in VS Code settings or rust-analyzer config:

// .vscode/settings.json
{
  "rust-analyzer.check.command": "clippy",
  "rust-analyzer.check.extraArgs": [
    "--all-targets",
    "--all-features",
    "--",
    "-W",
    "clippy::pedantic",
    "-W",
    "clippy::nursery"
  ],
  "rust-analyzer.checkOnSave": true
}

Or in rust-analyzer.toml:

# rust-analyzer.toml
[checkOnSave]
command = "clippy"
extraArgs = [
  "--all-targets",
  "--all-features",
  "--",
  "-W", "clippy::pedantic",
  "-W", "clippy::nursery",
  "-A", "clippy::module_name_repetitions"
]

Disallowed Methods Configuration

# clippy.toml
disallowed-methods = [
  # Prevent unwrap/expect in production code
  { path = "std::option::Option::unwrap", reason = "Use unwrap_or, unwrap_or_else, or proper error handling" },
  { path = "std::result::Result::unwrap", reason = "Use unwrap_or, unwrap_or_else, or the ? operator" },
  { path = "std::option::Option::expect", reason = "Use unwrap_or, unwrap_or_else, or proper error handling" },
  { path = "std::result::Result::expect", reason = "Use unwrap_or, unwrap_or_else, or the ? operator" },

  # Prevent panic
  { path = "std::panic", reason = "Use Result and proper error handling" },

  # Prevent process::exit
  { path = "std::process::exit", reason = "Return from main or propagate errors" },

  # Environment variable handling
  { path = "std::env::var", reason = "Use std::env::var_os for better Unicode handling" },

  # Prevent direct println! in libraries
  { path = "std::println", reason = "Use logging (log, tracing) instead of println" },
  { path = "std::eprintln", reason = "Use logging (log, tracing) instead of eprintln" },
]

disallowed-types = [
  # Prefer newer stdlib types
  { path = "std::sync::mpsc::channel", reason = "Use crossbeam-channel for better performance" },
  { path = "std::collections::HashMap", reason = "Consider indexmap for deterministic ordering" },

  # Deprecated types
  { path = "std::mem::uninitialized", reason = "Use MaybeUninit instead" },
]

Advanced Patterns

Conditional Linting for Tests

// src/lib.rs
#![deny(clippy::unwrap_used)]

// tests/integration.rs
#![allow(clippy::unwrap_used)]  // Ok in tests

#[cfg(test)]
mod tests {
    // Tests can use unwrap
    #[test]
    fn test_something() {
        let value = Some(42);
        assert_eq!(value.unwrap(), 42);
    }
}

Feature-gated Lints

#[cfg(not(feature = "unsafe_optimizations"))]
#![deny(unsafe_code)]

#[cfg(feature = "unsafe_optimizations")]
#![warn(unsafe_code)]

Documentation Lints

// Enforce documentation
#![warn(missing_docs)]
#![warn(clippy::missing_docs_in_private_items)]

/// Public function documentation
pub fn public_function() {
    // ...
}

/// Private function documentation (if pedantic enabled)
fn private_function() {
    // ...
}

Best Practices

Start with defaults, gradually enable stricter lints:

[workspace.lints.clippy]
all = "warn"
correctness = "deny"

Use Cargo.toml for workspace-wide configuration:

[workspace.lints.clippy]
# All crates inherit these

Document why lints are suppressed:

#[allow(clippy::cast_possible_truncation)]  // Value range validated above
let x = value as u8;

Treat warnings as errors in CI:
```
- run: cargo clippy -- -D warnings
```

Enable pedantic selectively:

pedantic = "warn"
must_use_candidate = "allow"  # Too noisy

Use disallowed-methods for project-specific rules:

disallowed-methods = [
  { path = "std::println", reason = "Use tracing instead" }
]

Integrate with rust-analyzer for real-time feedback
Review and update configuration as project matures

Troubleshooting

Too many warnings:

# Start with just correctness
cargo clippy -- -W clippy::correctness
# Gradually enable more

False positives:

#[allow(clippy::specific_lint)]  // Document why
fn special_case() { }

Lint not applying:

# Check clippy version
cargo clippy --version
# Update toolchain
rustup update

CI failures due to new lints:

# Pin clippy version in rust-toolchain.toml
[toolchain]
channel = "1.75.0"
components = ["clippy"]

clippy-advanced