cargo-llvm-cov

Cargo subcommand to easily use LLVM source-based code coverage.

This is a wrapper around rustc -C instrument-coverage and provides:

• Generate very precise coverage data. (line, region, and branch coverage. branch coverage is currently optional and requires nightly, see #8 for more)
• Support cargo test, cargo run, and cargo nextest with command-line interface compatible with cargo.
• Support for proc-macro, including coverage of UI tests.
• Support for doc tests. (this is currently optional and requires nightly, see #2 for more)
• Fast because it does not introduce extra layers between rustc, cargo, and llvm-tools.

Table of Contents:

• Usage
  • Basic usage
  • Merge coverages generated under different test conditions
  • Get coverage of C/C++ code linked to Rust library/binary
  • Get coverage of external tests
  • Exclude file from coverage
  • Exclude code from coverage
  • Continuous Integration
  • Display coverage in VS Code
  • Environment variables
  • Additional JSON information
• Installation
• Known limitations
• Related Projects
• License

Usage

Basic usage

Click to show a complete list of options

(See docs directory for options of subcommands)

$ cargo llvm-cov --help
cargo-llvm-cov
Cargo subcommand to easily use LLVM source-based code coverage (-C instrument-coverage).

USAGE:
    cargo llvm-cov [SUBCOMMAND] [OPTIONS] [-- <args>...]

ARGS:
    <args>...
            Arguments for the test binary

OPTIONS:
        --json
            Export coverage data in "json" format

            If --output-path is not specified, the report will be printed to stdout.

            This internally calls `llvm-cov export -format=text`. See
            <https://llvm.org/docs/CommandGuide/llvm-cov.html#llvm-cov-export> for more.

        --lcov
            Export coverage data in "lcov" format

            If --output-path is not specified, the report will be printed to stdout.

            This internally calls `llvm-cov export -format=lcov`. See
            <https://llvm.org/docs/CommandGuide/llvm-cov.html#llvm-cov-export> for more.

        --cobertura
            Export coverage data in "cobertura" XML format

            If --output-path is not specified, the report will be printed to stdout.

            This internally calls `llvm-cov export -format=lcov` and then converts to cobertura.xml.
            See <https://llvm.org/docs/CommandGuide/llvm-cov.html#llvm-cov-export> for more.

        --codecov
            Export coverage data in "Codecov Custom Coverage" format

            If --output-path is not specified, the report will be printed to stdout.

            This internally calls `llvm-cov export -format=json` and then converts to codecov.json.
            See <https://llvm.org/docs/CommandGuide/llvm-cov.html#llvm-cov-export> for more.

        --text
            Generate coverage report in “text” format

            If --output-path or --output-dir is not specified, the report will be printed to stdout.

            This internally calls `llvm-cov show -format=text`. See
            <https://llvm.org/docs/CommandGuide/llvm-cov.html#llvm-cov-show> for more.

        --html
            Generate coverage report in "html" format

            If --output-dir is not specified, the report will be generated in `target/llvm-cov/html`
            directory.

            This internally calls `llvm-cov show -format=html`. See
            <https://llvm.org/docs/CommandGuide/llvm-cov.html#llvm-cov-show> for more.

        --open
            Generate coverage reports in "html" format and open them in a browser after the
            operation.

            See --html for more.

        --summary-only
            Export only summary information for each file in the coverage data

            This flag can only be used together with --json, --lcov, or --cobertura.

        --output-path <PATH>
            Specify a file to write coverage data into.

            This flag can only be used together with --json, --lcov, --cobertura, or --text.
            See --output-dir for --html and --open.

        --output-dir <DIRECTORY>
            Specify a directory to write coverage report into (default to `target/llvm-cov`).

            This flag can only be used together with --text, --html, or --open. See also
            --output-path.

        --failure-mode <any|all>
            Fail if `any` or `all` profiles cannot be merged (default to `any`)

        --ignore-filename-regex <PATTERN>
            Skip source code files with file paths that match the given regular expression

        --show-instantiations
            Show instantiations in report

        --no-cfg-coverage
            Unset cfg(coverage), which is enabled when code is built using cargo-llvm-cov

        --no-cfg-coverage-nightly
            Unset cfg(coverage_nightly), which is enabled when code is built using cargo-llvm-cov
            and nightly compiler

        --no-report
            Run tests, but don't generate coverage report

        --no-clean
            Build without cleaning any old build artifacts

        --fail-under-functions <MIN>
            Exit with a status of 1 if the total function coverage is less than MIN percent

        --fail-under-lines <MIN>
            Exit with a status of 1 if the total line coverage is less than MIN percent

        --fail-under-regions <MIN>
            Exit with a status of 1 if the total region coverage is less than MIN percent

        --fail-uncovered-lines <MAX>
            Exit with a status of 1 if the uncovered lines are greater than MAX

        --fail-uncovered-regions <MAX>
            Exit with a status of 1 if the uncovered regions are greater than MAX

        --fail-uncovered-functions <MAX>
            Exit with a status of 1 if the uncovered functions are greater than MAX

        --show-missing-lines
            Show lines with no coverage

        --include-build-script
            Include build script in coverage report

        --dep-coverage <NAME>
            Show coverage of the specified dependency instead of the crates in the current workspace. (unstable)

        --skip-functions
            Skip exporting per-function coverage data.

            This flag can only be used together with --json, --lcov, or --cobertura.

        --branch
            Enable branch coverage. (unstable)

        --mcdc
            Enable mcdc coverage. (unstable)

        --doctests
            Including doc tests (unstable)

            This flag is unstable. See <https://github.com/taiki-e/cargo-llvm-cov/issues/2> for
            more.

        --no-run
            Generate coverage report without running tests

        --no-fail-fast
            Run all tests regardless of failure

        --ignore-run-fail
            Run all tests regardless of failure and generate report

            If tests failed but report generation succeeded, exit with a status of 0.

    -q, --quiet
            Display one character per test instead of one line

        --lib
            Test only this package's library unit tests

        --bin <NAME>
            Test only the specified binary

        --bins
            Test all binaries

        --example <NAME>
            Test only the specified example

        --examples
            Test all examples

        --test <NAME>
            Test only the specified test target

        --tests
            Test all tests

        --bench <NAME>
            Test only the specified bench target

        --benches
            Test all benches

        --all-targets
            Test all targets

        --doc
            Test only this library's documentation (unstable)

            This flag is unstable because it automatically enables --doctests flag. See
            <https://github.com/taiki-e/cargo-llvm-cov/issues/2> for more.

    -p, --package <SPEC>
            Package to run tests for

        --workspace
            Test all packages in the workspace

        --all
            Alias for --workspace (deprecated)

        --exclude <SPEC>
            Exclude packages from both the test and report

        --exclude-from-test <SPEC>
            Exclude packages from the test (but not from the report)

        --exclude-from-report <SPEC>
            Exclude packages from the report (but not from the test)

    -j, --jobs <N>
            Number of parallel jobs, defaults to # of CPUs

    -r, --release
            Build artifacts in release mode, with optimizations

        --profile <PROFILE-NAME>
            Build artifacts with the specified profile

    -F, --features <FEATURES>
            Space or comma separated list of features to activate

        --all-features
            Activate all available features

        --no-default-features
            Do not activate the `default` feature

        --target <TRIPLE>
            Build for the target triple

            When this option is used, coverage for proc-macro and build script will not be displayed
            because cargo does not pass RUSTFLAGS to them.

        --coverage-target-only
            Activate coverage reporting only for the target triple

            Activate coverage reporting only for the target triple specified via `--target`. This is
            important, if the project uses multiple targets via the cargo bindeps feature, and not
            all targets can use `instrument-coverage`, e.g. a microkernel, or an embedded binary.

    -v, --verbose
            Use verbose output

            Use -vv (-vvv) to propagate verbosity to cargo.

        --color <WHEN>
            Coloring: auto, always, never

        --remap-path-prefix
            Use --remap-path-prefix for workspace root

            Note that this does not fully compatible with doctest.

        --include-ffi
            Include coverage of C/C++ code linked to Rust library/binary

            Note that `CC`/`CXX`/`LLVM_COV`/`LLVM_PROFDATA` environment variables must be set to
            Clang/LLVM compatible with the LLVM version used in rustc.

        --keep-going
            Do not abort the build as soon as there is an error (unstable)

        --ignore-rust-version
            Ignore `rust-version` specification in packages

        --manifest-path <PATH>
            Path to Cargo.toml

        --frozen
            Require Cargo.lock and cache are up to date

        --locked
            Require Cargo.lock is up to date

        --offline
            Run without accessing the network

    -Z <FLAG>
            Unstable (nightly-only) flags to Cargo, see 'cargo -Z help' for
            details

    -h, --help
            Print help information

    -V, --version
            Print version information

SUBCOMMANDS:
    test
            Run tests and generate coverage report
            This is equivalent to `cargo llvm-cov` without subcommand,
            except that test name filtering is supported.
    run
            Run a binary or example and generate coverage report
    report
            Generate coverage report
    show-env
            Output the environment set by cargo-llvm-cov to build Rust projects
    clean
            Remove artifacts that cargo-llvm-cov has generated in the past
    nextest
            Run tests with cargo nextest
            This internally calls `cargo nextest run`.

By default, run tests (via cargo test), and print the coverage summary to stdout.

cargo llvm-cov

Currently, doc tests are disabled by default because nightly-only features are required to make coverage work for doc tests. see #2 for more.

To run cargo run instead of cargo test, use run subcommand.

cargo llvm-cov run

With html report (the report will be generated to target/llvm-cov/html directory):

cargo llvm-cov --html
open target/llvm-cov/html/index.html

or

cargo llvm-cov --open

With plain text report (if --output-path is not specified, the report will be printed to stdout):

cargo llvm-cov --text | less -R

With json report (if --output-path is not specified, the report will be printed to stdout):

cargo llvm-cov --json --output-path cov.json

With lcov report (if --output-path is not specified, the report will be printed to stdout):

cargo llvm-cov --lcov --output-path lcov.info

You can get a coverage report in a different format based on the results of a previous run by using cargo llvm-cov report.

cargo llvm-cov --html          # run tests and generate html report
cargo llvm-cov report --lcov # generate lcov report

cargo llvm-cov/cargo llvm-cov run/cargo llvm-cov nextest cleans some build artifacts by default to avoid false positives/false negatives due to old build artifacts. This behavior is disabled when --no-clean, --no-report, or --no-run is passed, and old build artifacts are retained. When using these flags, it is recommended to first run cargo llvm-cov clean --workspace to remove artifacts that may affect the coverage results.

cargo llvm-cov clean --workspace # remove artifacts that may affect the coverage results
cargo llvm-cov --no-clean

Merge coverages generated under different test conditions

You can merge the coverages generated under different test conditions by using --no-report and cargo llvm-cov report.

cargo llvm-cov clean --workspace # remove artifacts that may affect the coverage results
cargo llvm-cov --no-report --features a
cargo llvm-cov --no-report --features b
cargo llvm-cov report --lcov # generate report without tests

Note: To include coverage for doctests you also need to pass --doctests to cargo llvm-cov report.

Get coverage of C/C++ code linked to Rust library/binary

Set CC, CXX, LLVM_COV, and LLVM_PROFDATA environment variables to Clang/LLVM compatible with the LLVM version used in rustc, and run cargo-llvm-cov with --include-ffi flag.

CC=<clang-path> \
CXX=<clang++-path> \
LLVM_COV=<llvm-cov-path> \
LLVM_PROFDATA=<llvm-profdata-path> \
  cargo llvm-cov --lcov --include-ffi

Known compatible Rust (installed via rustup) and LLVM versions:

	Rust 1.60-1.77	Rust 1.78-1.81	Rust 1.82-1.84
LLVM 14-17	ok
LLVM 18		ok
LLVM 19			ok

Get coverage of external tests

cargo test, cargo run, and cargo nextest are available as builtin, but cargo-llvm-cov can also be used for arbitrary binaries built using cargo (including other cargo subcommands or external tests that use make, xtask, etc.)

# Set the environment variables needed to get coverage.
source <(cargo llvm-cov show-env --export-prefix)
# Remove artifacts that may affect the coverage results.
# This command should be called after show-env.
cargo llvm-cov clean --workspace
# Above two commands should be called before build binaries.

cargo build # Build rust binaries.
# Commands using binaries in target/debug/*, including `cargo test` and other cargo subcommands.
# ...

cargo llvm-cov report --lcov # Generate report without tests.

Note: cargo-llvm-cov subcommands other than report and clean may not work correctly in the context where environment variables are set by show-env; consider using normal cargo/cargo-nextest commands.

Note: To include coverage for doctests you also need to pass --doctests to both cargo llvm-cov show-env and cargo llvm-cov report.

Exclude file from coverage

To exclude specific file patterns from the report, use the --ignore-filename-regex option.

cargo llvm-cov --open --ignore-filename-regex build

Exclude code from coverage

To exclude the specific function or module from coverage, use the #[coverage(off)] attribute.

Since #[coverage(off)] attribute stabilized in Rust 1.85, it is recommended to use it together with cfg(coverage) or cfg(coverage_nightly) set by cargo-llvm-cov for compatibility with old Rust.

// function
#[cfg_attr(coverage, coverage(off))]
fn exclude_fn_from_coverage() {
    // ...
}

// module
#[cfg_attr(coverage, coverage(off))]
mod exclude_mod_from_coverage {
    // ...
}

cfgs are set under the following conditions:

• cfg(coverage) is always set when using cargo-llvm-cov (unless --no-cfg-coverage flag passed)
• cfg(coverage_nightly) is set when using cargo-llvm-cov with nightly toolchain (unless --no-cfg-coverage-nightly flag passed)

Rust 1.80+ warns the above cfgs as unexpected_cfgs. The recommended way to address this is to add a lints table to Cargo.toml.

[lints.rust]
unexpected_cfgs = { level = "warn", check-cfg = ['cfg(coverage,coverage_nightly)'] }

If you want to ignore all #[test]-related code, you can use module-level #[coverage(off)] attribute:

#[cfg(test)]
#[cfg_attr(coverage, coverage(off))]
mod tests {
    // ...
}

cargo-llvm-cov excludes code contained in the directory named tests from the report by default, so you can also use it instead of #[coverage(off)] attribute.

Continuous Integration

Here is an example of GitHub Actions workflow that uploads coverage to Codecov.

name: Coverage

on: [pull_request, push]

jobs:
  coverage:
    runs-on: ubuntu-latest
    env:
      CARGO_TERM_COLOR: always
    steps:
      - uses: actions/checkout@v4
      - name: Install Rust
        run: rustup update stable
      - name: Install cargo-llvm-cov
        uses: taiki-e/install-action@cargo-llvm-cov
      - name: Generate code coverage
        run: cargo llvm-cov --all-features --workspace --lcov --output-path lcov.info
      - name: Upload coverage to Codecov
        uses: codecov/codecov-action@v3
        with:
          token: ${{ secrets.CODECOV_TOKEN }} # not required for public repos
          files: lcov.info
          fail_ci_if_error: true

Currently, when using --lcov flag, only line coverage is available on Codecov.

By using --codecov flag instead of --lcov flag, you can use region coverage on Codecov:

- name: Generate code coverage
  run: cargo llvm-cov --all-features --workspace --codecov --output-path codecov.json
- name: Upload coverage to Codecov
  uses: codecov/codecov-action@v3
  with:
    token: ${{ secrets.CODECOV_TOKEN }} # not required for public repos
    files: codecov.json
    fail_ci_if_error: true

Note that the way Codecov shows region/branch coverage is not very good.

Display coverage in VS Code

You can display coverage in VS Code using Coverage Gutters.

Coverage Gutters supports lcov style coverage file and detects lcov.info files at the top level or in the coverage directory. Below is an example command to generate the coverage file.

cargo llvm-cov --lcov --output-path lcov.info

You may need to click the "Watch" label in the bottom bar of VS Code to display coverage.

Environment variables

You can override these environment variables to change cargo-llvm-cov's behavior on your system:

• CARGO_LLVM_COV_TARGET_DIR -- Location of where to place all generated artifacts, relative to the current working directory. Default to <cargo_target_dir>/llvm-cov-target.
• CARGO_LLVM_COV_SETUP -- Control behavior if llvm-tools-preview component is not installed. See #219 for more.
• LLVM_COV -- Override the path to llvm-cov. You may need to specify both this and LLVM_PROFDATA environment variables if you are using --include-ffi flag or if you are using a toolchain installed without via rustup. llvm-cov version must be compatible with the LLVM version used in rustc.
• LLVM_PROFDATA -- Override the path to llvm-profdata. See LLVM_COV environment variable for more.
• LLVM_COV_FLAGS -- A space-separated list of additional flags to pass to all llvm-cov invocations that cargo-llvm-cov performs. See LLVM documentation for available options.
• LLVM_PROFDATA_FLAGS -- A space-separated list of additional flags to pass to all llvm-profdata invocations that cargo-llvm-cov performs. See LLVM documentation for available options.
• LLVM_PROFILE_FILE_NAME -- Override the file name (the final component of the path) of the LLVM_PROFILE_FILE. See LLVM documentation for available syntax.

See also environment variables that Cargo reads. cargo-llvm-cov respects many of them.

Additional JSON information

If JSON is selected as output format (with the --json flag), then cargo-llvm-cov will add additional contextual information at the root of the llvm-cov data. This can be helpful for programs that rely on the output of cargo-llvm-cov.

{
  // Other regular llvm-cov fields ...
  "cargo_llvm_cov": {
    "version": "0.0.0",
    "manifest_path": "/path/to/your/project/Cargo.toml"
  }
}

• version specifies the version of cargo-llvm-cov that was used. This allows other programs to verify a certain version of it was used and make assertions of its behavior.
• manifest_path defines the absolute path to the Rust project's Cargo.toml that cargo-llvm-cov was executed on. It can help to avoid repeating the same option on both programs.

For example, when forwarding the JSON output directly to another program:

cargo-llvm-cov --json | some-program

Installation

From source

cargo +stable install cargo-llvm-cov --locked

Currently, installing cargo-llvm-cov requires rustc 1.73+ for non-Windows and rustc 1.74+ for Windows.

cargo-llvm-cov is usually runnable with Cargo versions older than the Rust version required for installation (e.g., cargo +1.60 llvm-cov). Currently, to run cargo-llvm-cov requires Cargo 1.60+.

From prebuilt binaries

You can download prebuilt binaries from the Release page. Prebuilt binaries are available for macOS, Linux (gnu and musl), Windows (static executable), and FreeBSD.

Example of script to download cargo-llvm-cov

# Get host target
host=$(rustc -vV | grep '^host:' | cut -d' ' -f2)
# Download binary and install to $HOME/.cargo/bin
curl --proto '=https' --tlsv1.2 -fsSL https://github.com/taiki-e/cargo-llvm-cov/releases/latest/download/cargo-llvm-cov-$host.tar.gz | tar xzf - -C "$HOME/.cargo/bin"

On GitHub Actions

You can use taiki-e/install-action to install prebuilt binaries on Linux, macOS, and Windows. This makes the installation faster and may avoid the impact of problems caused by upstream changes.

- uses: taiki-e/install-action@cargo-llvm-cov

When used with nextest:

- uses: taiki-e/install-action@cargo-llvm-cov
- uses: taiki-e/install-action@nextest

Via Homebrew

You can install cargo-llvm-cov from the Homebrew tap maintained by us (x86_64/AArch64 macOS, x86_64/AArch64 Linux):

brew install taiki-e/tap/cargo-llvm-cov

Alternatively, you can install cargo-llvm-cov from homebrew-core (x86_64/AArch64 macOS, x86_64 Linux):

brew install cargo-llvm-cov

Via Scoop (Windows)

You can install cargo-llvm-cov from the Scoop bucket maintained by us:

scoop bucket add taiki-e https://github.com/taiki-e/scoop-bucket
scoop install cargo-llvm-cov

Via cargo-binstall

You can install cargo-llvm-cov using cargo-binstall:

cargo binstall cargo-llvm-cov

Via pacman (Arch Linux)

You can install cargo-llvm-cov from the extra repository:

pacman -S cargo-llvm-cov

Known limitations

• Support for branch coverage is unstable. See #8 and rust-lang/rust#79649 for more.
• Support for doc tests is unstable and has known issues. See #2 and rust-lang/rust#79417 for more.

See also the code-coverage-related issues reported in rust-lang/rust.

Related Projects

• cargo-config2: Library to load and resolve Cargo configuration. cargo-llvm-cov uses this library.
• cargo-hack: Cargo subcommand to provide various options useful for testing and continuous integration.
• cargo-minimal-versions: Cargo subcommand for proper use of -Z minimal-versions.

License

Licensed under either of Apache License, Version 2.0 or MIT license at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.