bin+lib grcov

Rust tool to collect and aggregate code coverage data for multiple source files

27 releases

new 0.8.2 Jul 30, 2021
0.8.0 Apr 21, 2021
0.7.1 Jan 21, 2021
0.6.1 Nov 27, 2020
0.3.0 Oct 9, 2018

#5 in Testing

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Used in 3 crates

MPL-2.0 license



Build Status Build status codecov crates.io

grcov collects and aggregates code coverage information for multiple source files. grcov processes .profraw and .gcda files which can be generated from llvm/clang or gcc. grcov also processes lcov files (for JS coverage) and JaCoCo files (for Java coverage). Linux, macOS and Windows are supported.

This is a project initiated by Mozilla to gather code coverage results on Firefox.

Table of Contents

man grcov

    grcov [FLAGS] [OPTIONS] <paths>...

            Enables parsing branch coverage information


    -h, --help
            Prints help information

            Ignore source files that can't be found on the disk

            Speeds-up parsing, when the code coverage information is exclusively coming from a llvm build

            Sets the build type to be parallel for 'coveralls' and 'coveralls+' formats

    -V, --version
            Prints version information

    -b, --binary-path <PATH>
            Sets the path to the directory containing the compiled binaries to be used

        --commit-sha <COMMIT HASH>
            Sets the hash of the commit used to generate the code coverage data

        --excl-br-line <regex>
            Lines in covered files containing this marker will be excluded from branch coverage.

        --excl-br-start <regex>
            Marks the beginning of a section excluded from branch coverage. The current line is part of this section.

        --excl-br-stop <regex>
            Marks the end of a section excluded from branch coverage. The current line is part of this section.

        --excl-line <regex>
            Lines in covered files containing this marker will be excluded.

        --excl-start <regex>
            Marks the beginning of an excluded section. The current line is part of this section.

        --excl-stop <regex>
            Marks the end of an excluded section. The current line is part of this section.

        --filter <filter>
            Filters out covered/uncovered files. Use 'covered' to only return covered files, 'uncovered' to only return
            uncovered files [possible values: covered, uncovered]
        --ignore <PATH>...
            Ignore files/directories specified as globs

        --keep-only <PATH>...
            Keep only files/directories specified as globs

        --log <LOG>
            Set the file where to log (or stderr or stdout). Defaults to 'stderr' [default: stderr]

    -o, --output-path <PATH>
            Specifies the output path

    -t, --output-type <OUTPUT TYPE>
            Sets a custom output type:
            - *html* for a HTML coverage report;
            - *coveralls* for the Coveralls specific format;
            - *lcov* for the lcov INFO format;
            - *covdir* for the covdir recursive JSON format;
            - *coveralls+* for the Coveralls specific format with function information;
            - *ade* for the ActiveData-ETL specific format;
            - *cobertura* for a cobertura coverage report;
            - *files* to only return a list of files.
             [default: lcov]  [possible values: ade, lcov, coveralls, coveralls+, files, covdir, html, cobertura]
        --path-mapping <PATH>...

    -p, --prefix-dir <PATH>
            Specifies a prefix to remove from the paths (e.g. if grcov is run on a different machine than the one that
            generated the code coverage information)
        --service-job-id <SERVICE JOB ID>
            Sets the service job id [aliases: service-job-number]

        --service-name <SERVICE NAME>
            Sets the service name

        --service-number <SERVICE NUMBER>
            Sets the service number

        --service-pull-request <SERVICE PULL REQUEST>
            Sets the service pull request number

    -s, --source-dir <DIRECTORY>
            Specifies the root directory of the source files

        --threads <NUMBER>
             [default: 11]

        --token <TOKEN>
            Sets the repository token from Coveralls, required for the 'coveralls' and 'coveralls+' formats

        --vcs-branch <VCS BRANCH>
            Set the branch for coveralls report. Defaults to 'master' [default: master]

            Sets the input paths to use

How to get grcov

Grcov can be downloaded from releases or, if you have Rust installed, you can run cargo install grcov.


Nightly Rust is required to use grcov for Rust coverage. Alternatively, you can export RUSTC_BOOTSTRAP=1, which basically turns your stable rustc into a Nightly one.

Example: How to generate source-based coverage for a Rust project

  1. Install the llvm-tools or llvm-tools-preview component:

    rustup component add llvm-tools-preview
  2. Ensure that the following environment variable is set up:

    export RUSTFLAGS="-Zinstrument-coverage"
  3. Build your code:

    cargo build

  4. Ensure each test runs gets its own profile information by defining the LLVM_PROFILE_FILE environment variable (%p will be replaced by the process ID, and %m by the binary signature):

    export LLVM_PROFILE_FILE="your_name-%p-%m.profraw"
  5. Run your tests:

    cargo test

In the CWD, you will see a .profraw file has been generated. This contains the profiling information that grcov will parse, alongside with your binaries.

Example: How to generate .gcda files for C/C++

Pass --coverage to clang or gcc (or for older gcc versions pass -ftest-coverage and -fprofile-arcs options (see gcc docs).

Example: How to generate .gcda files for a Rust project

  1. Ensure that the following environment variables are set up:

    export RUSTFLAGS="-Zprofile -Ccodegen-units=1 -Copt-level=0 -Clink-dead-code -Coverflow-checks=off -Zpanic_abort_tests -Cpanic=abort"
    export RUSTDOCFLAGS="-Cpanic=abort"

    These will ensure that things like dead code elimination do not skew the coverage.

  2. Build your code:

    cargo build

    If you look in target/debug/deps dir you will see .gcno files have appeared. These are the locations that could be covered.

  3. Run your tests:

    cargo test

    In the target/debug/deps/ dir you will now also see .gcda files. These contain the hit counts on which of those locations have been reached. Both sets of files are used as inputs to grcov.

Generate a coverage report from coverage artifacts

Generate a html coverage report like this:

grcov . -s . --binary-path ./target/debug/ -t html --branch --ignore-not-existing -o ./target/debug/coverage/

N.B.: The --binary-path argument is only necessary for source-based coverage.

You can see the report in target/debug/coverage/index.html.

(or alternatively with -t lcov grcov will output a lcov compatible coverage report that you could then feed into lcov's genhtml command).

LCOV output

By passing -t lcov you could generate an lcov.info file and pass it to genhtml:

genhtml -o ./target/debug/coverage/ --show-details --highlight --ignore-errors source --legend ./target/debug/lcov.info

LCOV output should be used when uploading to Codecov, with the --branch argument for branch coverage support.

Coveralls output

Coverage can also be generated in coveralls format:

grcov . --binary-path ./target/debug/ -t coveralls -s . --token YOUR_COVERALLS_TOKEN > coveralls.json

grcov with Travis

Here is an example of .travis.yml file for source-based coverage:

language: rust

  - curl -L https://github.com/mozilla/grcov/releases/latest/download/grcov-linux-x86_64.tar.bz2 | tar jxf -

    - os: linux
      rust: nightly

    - rustup component add llvm-tools-preview
    - export RUSTFLAGS="-Zinstrument-coverage"
    - cargo build --verbose
    - LLVM_PROFILE_FILE="your_name-%p-%m.profraw" cargo test --verbose
    - ./grcov . --binary-path ./target/debug/ -s . -t lcov --branch --ignore-not-existing --ignore "/*" -o lcov.info
    - bash <(curl -s https://codecov.io/bash) -f lcov.info

Here is an example of .travis.yml file:

language: rust

  - curl -L https://github.com/mozilla/grcov/releases/latest/download/grcov-linux-x86_64.tar.bz2 | tar jxf -

    - os: linux
      rust: nightly

    - export CARGO_INCREMENTAL=0
    - export RUSTFLAGS="-Zprofile -Ccodegen-units=1 -Copt-level=0 -Clink-dead-code -Coverflow-checks=off -Zpanic_abort_tests -Cpanic=abort"
    - export RUSTDOCFLAGS="-Cpanic=abort"
    - cargo build --verbose $CARGO_OPTIONS
    - cargo test --verbose $CARGO_OPTIONS
    - |
      zip -0 ccov.zip `find . \( -name "YOUR_PROJECT_NAME*.gc*" \) -print`;
      ./grcov ccov.zip -s . -t lcov --llvm --branch --ignore-not-existing --ignore "/*" -o lcov.info;
      bash <(curl -s https://codecov.io/bash) -f lcov.info;

Alternative reports

grcov provides the following output types:

Output Type -t Description
lcov (default) lcov's INFO format that is compatible with the linux coverage project.
ade ActiveData-ETL format. Only useful for Mozilla projects.
coveralls Generates coverage in Coveralls format.
coveralls+ Like coveralls but with function level information.
files Output a file list of covered or uncovered source files.
covdir Provides coverage in a recursive JSON format.
html Output a HTML coverage report, including coverage badges for your README.

Hosting HTML reports and using coverage badges

The HTML report can be hosted on static website providers like GitHub Pages, Netlify and others. It is common to provide a coverage badge in a project's readme to show the current percentage of covered code.

To still allow adding the badge when using a static site host, grcov generates coverage badges and a JSON file with coverage information that can be used with https://shields.io to dynamically generate badges.

The coverage data for htttps://shields.io can be found at /coverage.json and the generated bagdes are available as SVGs at /badges/*svg.

The design of generated badges is taken from shields.io but may not be updated immediately if there is any change. Using their endpoint method is recommended if other badges from their service are used already.


Let's consider we have a project at with username sample and project awesome that is hosted with GitHub Pages at https://sample.github.io/awesome.

By using the the shields.io endpoint we can create a Markdown badge like so:


If we want to avoid using shields.io as well, we can use the generated badges as follows (note the different URL for the image):



This project is using pre-commit. Please run pre-commit install to install the git pre-commit hooks on your clone. Instructions on how to install pre-commit can be found here.

Every time you will try to commit, pre-commit will run checks on your files to make sure they follow our style standards and they aren't affected by some simple issues. If the checks fail, pre-commit won't let you commit.

Build & Test

Build with:

cargo build

To run unit tests:

cargo test --lib

To run integration tests, it is suggested to use the Docker image defined in tests/Dockerfile. Simply build the image to run them:

docker build -t marcocas/grcov -f tests/Dockerfile .

Otherwise, if you don't want to use Docker, the only prerequisite is to install GCC 7, setting the GCC_CXX environment variable to g++-7 and the GCOV environment variable to gcov-7. Then run the tests with:

cargo test

Minimum requirements

  • GCC 4.9 or higher is required (if parsing coverage artifacts generated by GCC).


Published under the MPL 2.0 license.


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