Using Bazel to generate coverage report - code-coverage

Question

I am using genhtml command to generate html coverage report from Bazel generated coverage.dat file:
genhtml bazel-testlogs/path/to/TestTarget/coverage.dat --output-directory coverage
The problem with using genhtml is that I have to provide the paths to the coverage.dat files (which are generated in bazel-testlogs/..) Is it possible to fetch those coverage.dat files as an output from another rule?
I would like to not have to call genthml command directly, but have Bazel handle everything.

Answer 1

I was not able to find a way to get coverage.dat files as an output of a bazel rule. However, I was able to wrap all the locations of all the .dat files as srcs to a filegroup in WORKSPACE directory:
filegroup(
name = "coverage_files",
srcs = glob(["bazel-out/**/coverage.dat"]),
)
and then use that filegroup in a custom .bzl rule that wraps the genthml command to generate html coverage report. So now I only have to call
bazel coverage //path/... --instrumentation_filter=/path[/:]
command to generate the coverage.dat files, generate html report and zip it up. Thus, bazel handles everything.

Answer 2

Bazel added support for C++ coverage (though I couldn't find much documentation for it).
I was able to generate a combined coverage.dat file with
bazel coverage -s \
--instrument_test_targets \
--experimental_cc_coverage \
--combined_report=lcov \
--coverage_report_generator=#bazel_tools//tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator:Main \
//...
The coverage file gets added to bazel-out/_coverage/_coverage_report.dat

Answer 3

For Java based project we can get code coverage in following way
To get coverage for complete module ->
Running coverage for complete project module. Run following command ->
bazel coverage ... --compilation_mode=dbg --subcommands --announce_rc --verbose_failures --jobs=auto --sandbox_debug --build_runfile_links --combined_report=lcov --coverage_report_generator=#bazel_tools//tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator:Main
Then run following command from parent project directory to get html view. Html report is generated in output-directory-name we specified. From that open index.html to see coverage report.
genhtml -o <output-directory-name> bazel-out/_coverage/_coverage_report.dat
bazel-out directory usually gets created in project parent directory(e.g. where bazel WORKSPACE file is present)
To get coverage for specific IT/Test in a module ->
Running coverage for for specific IT/Test in a module. Run following command from project/sub-project directory ->
bazel coverage <class-name-of-Test-or-IT> --compilation_mode=dbg --subcommands --announce_rc --verbose_failures --jobs=auto --sandbox_debug --build_runfile_links --combined_report=lcov --coverage_report_generator=#bazel_tools//tools/test/CoverageOutputGenerator/java/com/google/devtools/coverageoutputgenerator:Main
Then run following command from parent project directory to get html view. Html report is generated in output-directory-name we specified. From that open index.html to see coverage report.
genhtml -o <output-directory-name> bazel-out/_coverage/_coverage_report.dat