Code Quality

Automated collection of code quality metrics — unsafe code detection, binary size analysis, and documentation coverage — emitted as a single report artifact.

Reference

Field	Value
Workflow	`.github/workflows/code-quality.yml`
Tools	`cargo-geiger`, `cargo-bloat`, `rustdoc`
Output	Markdown report artifact

Metrics collected

Metric	Tool	What it detects
Unsafe code analysis	`cargo-geiger`	Unsafe function calls, blocks, trait impls, and unsafe in dependencies
Binary size analysis	`cargo-bloat`	Size by crate and by function; bloat sources
Documentation coverage	`rustdoc`	Missing doc comments, broken doc links, doc test failures

Report access

The workflow generates a combined report. Access it via Actions → Code Quality Metrics → Artifacts → code-quality-metrics.

Example report:

## Unsafe Code Analysis
Functions  Expressions  Impls  Traits  Methods  Dependency
0/10       0/100        0/5    0/2     0/20     rust_template

## Binary Size Analysis
File   .text   Size    Crate
 71.0%  59.0%   1.2MiB  std
  8.5%   7.1%   147KiB  rust_template

## Documentation Coverage
Documenting rust_template v0.1.0
warning: missing documentation for public function

Interpreting the unsafe code report

Functions  Expressions  Impls  Traits  Methods  Dependency
2/10       5/100        0/5    0/2     0/20     ✓ rust_template

Functions: 2 functions contain unsafe code.
Expressions: 5 unsafe expressions total.
✓ = no unsafe in this crate’s API.

Interpreting the binary size report

File   .text   Size    Crate
71.0%  59.0%   1.2MiB  std        ← Standard library
 8.5%   7.1%   147KiB  rust_template
 5.2%   4.3%   89KiB   serde

A large dependency contribution (e.g. serde) is a candidate for feature-flag trimming.

Interpreting documentation coverage

warning: missing documentation for public function `add`
  --> crates/lib.rs:10

Each warning names the public item that needs a doc comment.

How-to

Run the analysis locally

# Install tools
cargo install cargo-geiger cargo-bloat

# Run unsafe code analysis
cargo geiger --all-features

# Analyze binary size
cargo build --release
cargo bloat --release --crates

# Check documentation
cargo doc --no-deps --all-features

Verify: each command prints a report section matching the formats above.

Configure unsafe code policy

Set the unsafe policy in Cargo.toml:

[lints.rust]
unsafe_code = "forbid"  # No unsafe allowed
# or
unsafe_code = "warn"    # Warn but allow

Verify: cargo geiger reports 0/N for a forbid crate.

Configure binary size optimization

[profile.release]
opt-level = "z"        # Optimize for size
lto = true            # Link-time optimization
codegen-units = 1     # Better optimization
strip = true          # Remove symbols
panic = "abort"       # Smaller panic handler

Verify: cargo build --release && cargo bloat --release --crates and compare the total size.

Configure documentation requirements

[lints.rust]
missing_docs = "warn"                     # Warn on missing docs
rustdoc::broken_intra_doc_links = "deny"  # Fail on broken links

Verify: cargo doc --no-deps surfaces missing-doc warnings.

Improve the metrics

Reduce unsafe code — replace raw pointer writes with safe abstractions:

// Before
unsafe {
    *ptr = value;
}

// After - use safe abstraction
vec[index] = value;

Reduce binary size — find the largest contributors, then enable size optimizations:

cargo bloat --release -n 20

Improve documentation — add the missing doc comment the report named:

/// Adds two numbers together.
pub fn add(a: i64, b: i64) -> i64 {
    a + b
}

cargo doc --no-deps                          # Check coverage
cargo test --doc                             # Run doc tests
cargo doc --no-deps --document-private-items # Generate private docs

Verify: re-run the relevant tool and confirm the count dropped.

Troubleshooting

cargo-geiger errors:

cargo install cargo-geiger --force
cargo clean
cargo geiger

Binary size analysis fails — ensure a release build exists first:

cargo build --release
cargo bloat --release

Documentation warnings — surface them all as errors:

RUSTDOCFLAGS="-D warnings" cargo doc --no-deps

Why this matters

These three metrics each guard a property the compiler alone won’t enforce. unsafe_code = "forbid" is the template default, so cargo-geiger exists to confirm that guarantee holds transitively — unsafe code bypasses Rust’s safety model, and a dependency can reintroduce it silently. Binary size matters for download time and memory footprint, and cargo-bloat makes the cost of each dependency visible so feature trimming is an informed decision. Documentation coverage is a usability property: a well-documented public API is the difference between a crate people can adopt and one they have to reverse-engineer.