cargo-llvm-cov

Overview

cargo-llvm-cov is a Cargo subcommand for measuring Rust source coverage with rustc’s LLVM instrumentation. It suits Rust teams that want several report formats or need to include linked C and C++ code. Its range is a strength, but branch and doc-test coverage bring nightly requirements and instability.

As a command-line tool, it fits projects that already build and test through Cargo rather than readers looking for a standalone coverage dashboard. Free and open source, it offers broad output options without a paid plan; the trade-off is a Rust toolchain requirement and optional features that are not stable.

Key features

Line and region coverage form the stable core. Branch coverage is optional, requires nightly Rust, and remains unstable, so teams that depend on branch metrics should account for that constraint before adopting it.

It works with cargo test, cargo run, and cargo nextest, and supports proc-macro UI tests. Doc-test coverage is also optional, but requires nightly features and is unstable with known issues; projects relying heavily on doc tests should treat its results cautiously.

Reports can be produced as text, HTML, JSON, LCOV, Cobertura XML, or Codecov Custom Coverage format. That breadth makes the tool useful across local review and CI workflows: the README includes GitHub Actions examples for Codecov uploads and a GitLab CI example with Cobertura, while LCOV can be displayed in VS Code through Coverage Gutters.

With compatible Clang and LLVM tools configured, cargo-llvm-cov can include C and C++ coverage for code linked to a Rust library or binary. This is useful for mixed-language projects, though it depends on configuring those external tools.

Installation routes include Cargo source builds, prebuilt release binaries, GitHub Actions, Homebrew, Scoop, cargo-binstall, pacman, and FreeBSD ports. Installing requires rustc 1.87 or newer; running requires Cargo 1.60 or newer. Prebuilt binaries are listed for Linux, macOS, Windows, and FreeBSD. Releases are immutable, and releases since 0.8.5 publish artifact attestations with documented verification commands.

Pricing

Free / open source — free. The project is dual-licensed under Apache-2.0 or MIT, at the user's option, with no paid plans stated. That makes it a straightforward fit for individuals and teams seeking Rust coverage without a software subscription; the relevant costs are the toolchain and setup requirements, not a license fee.

Platforms

The software supports Linux, macOS, and Windows, with prebuilt binaries also listed for FreeBSD. Confirmed Windows targets include x86_64 and i686 MSVC, plus x86_64 and aarch64 GNU/LLVM MinGW. A self-hosted option and coverage gates are supported, useful for teams integrating coverage into their own CI processes.

Who it's for

Choose cargo-llvm-cov if your project uses Rust and you want a Cargo-native way to generate coverage for common test runners in several formats. It is particularly well suited to CI pipelines that need LCOV, Cobertura, or Codecov output, and to mixed Rust/C/C++ projects that can configure compatible Clang and LLVM tools.

It is a less comfortable fit when branch coverage or doc-test coverage must be stable: both are optional nightly features, and doc-test coverage has known issues. It also requires a recent rustc to install, so older toolchains may rule it out.

Pros and cons

• Pro: Multiple report formats, including LCOV and Cobertura XML, suit different editor and CI workflows.
• Pro: Support for cargo test, cargo run, and cargo nextest accommodates several common Rust test workflows.
• Pro: Compatible Clang and LLVM configuration can extend coverage to linked C and C++ code.
• Pro: Free, dual-licensed distribution avoids a paid plan requirement.
• Con: Branch coverage requires nightly Rust and remains unstable, limiting its appeal where branch metrics are central.
• Con: Doc-test coverage is unstable, nightly-dependent, and known to have issues.
• Con: Installing requires rustc 1.87 or newer, a hurdle for projects maintaining older toolchains.

Alternatives

Test Coverage Tools is a useful starting point for comparing coverage software across categories. Among the alternatives, the right choice depends chiefly on the language and workflow:

• OpenClover is another free option, with Linux, macOS, web, and Windows platforms and no usage limits or license keys in its free plan.
• SimpleCov is a free, MIT-licensed Ruby code coverage tool; choose it for Ruby rather than Rust.
• BullseyeCoverage offers a fully functional temporary evaluation license; consider it if that evaluation model suits your needs.
• Coverage.py is an open-source Python coverage tool with an enterprise subscription available through Tidelift; it fits Python projects.
• Coveralls is always free for open-source and public repositories, making it an option for those projects.
• Coverlet is a free, MIT-licensed option for modern .NET SDK-style projects.
• EclEmma is a free Eclipse plug-in for Java code coverage.
• gcov is a free alternative when code is compiled with GCC and coverage instrumentation is used to generate data.

Verdict

For Rust teams that want a free Cargo-native coverage tool with flexible reports—and, where configured, coverage of linked C and C++—cargo-llvm-cov is a strong fit. Choose it for that workflow breadth; look elsewhere if stable branch or doc-test coverage is essential, or if your project cannot meet its rustc installation minimum.