rules_scala supports coverage:
bazel coverage //...
It will produce several .dat files with results for your targets.
You can also add more options to receive a combined coverage report:
bazel coverage \
--combined_report=lcov \
--coverage_report_generator="@bazel_tools//tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator:Main" \
//...
This should produce a single bazel-out/_coverage/_coverage_report.dat
from all coverage files that are generated.
You can install lcov
package (that supports the format Bazel uses for coverage reports) to have access to additional tools:
# Use your system package manager. E.g. on Ubuntu:
sudo apt install lcov
Having lcov
package installed you can extract information from your coverage reports:
# For a summary:
lcov --summary your-coverage-report.dat
# For details:
lcov --list your-coverage-report.dat
If you prefer an HTML report, then you can use genhtml
provided also by the lcov
package.
An example with a bit of ceremony:
# Output html reports to a new directory.
destdir="my-coverage-reports"
mkdir -p ${destdir}
# Generate HTML report from the results.
genhtml -o ${destdir} --ignore-errors source bazel-out/_coverage/_coverage_report.dat
echo "coverage report at file://${destdir}/index.html"
Coverage support has been only tested with ScalaTest.
The current Jacoco version in Bazel (0.8.3) has missing coverage for lambdas
(including for comprehensions; see issue bazelbuild#1056).
This can be worked around by building a fixed version of Jacoco yourselves (including backported fixes from 0.8.5) and reconfiguring your
build to use that one instead of the default jacocorunner
.
You can build jacocorunner with a script in scripts/build_jacocorunner/build_jacocorunner.sh
(see comments there for more explanation and options).
Then, you can use the jacocorunner
property of scala_toolchain
to provide the jacocorunner you have built:
# Example contents of coverage_local_jacocorunner/BUILD
scala_toolchain(
name = "local_jacocorunner_toolchain_impl",
jacocorunner = ":local_jacocorunner",
visibility = ["//visibility:public"],
)
toolchain(
name = "local_jacocorunner_scala_toolchain",
toolchain = "local_jacocorunner_toolchain_impl",
toolchain_type = "@io_bazel_rules_scala//scala:toolchain_type",
visibility = ["//visibility:public"],
)
filegroup(
name = "local_jacocorunner",
srcs = ["JacocoCoverage_jarjar_deploy.jar"],
)
In this example jacocorunner
is provided as a local file, but you could also upload your version to an artifactory and then use http_file
(to avoid
keeping binaries in your repository).
Finally provide the scala_toolchain
in your .bazelrc
or as an option to bazel coverage
:
coverage --extra_toolchains="//coverage_local_jacocorunner:local_jacocorunner_scala_toolchain"
You can verify that the locally built jacocorunner
works with manual_test/coverage_local_jacocorunner/test.sh
.