Using Bazel to generate coverage report

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.

Indebtedness

Hi, Have you ever met ERROR: output '_coverage/_coverage_report.dat' was not created when run bazel coverage – Subantarctic

@Subantarctic Do not recall this particular error, this was a while ago... – Indebtedness

Hi, Can you remember the version of gcc you use to compile? – Subantarctic

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.

Indebtedness

Can you show how you used the filegroup and genhtml in combination to generate the final index.html coverage report? Did you use genrule? I added both filegroup and genrule in BUILD file in the root directory of my workspace but nothing seems to work. – Culch

@PavanManjunath not able to find all the code. I do have a custom .bzl file that uses run_shell with cmd to run python coverage html command, which generates the html file. Not sure if this is helpful, let me know if you need more info. – Indebtedness

@Indebtedness i don't understand, you can't post the code? or you can't find it? can you please share how you generate the HTML? – Maleficence

@sgammon Correct, I do not have access to the code, have been on a different project for years. To generate HTML file, I downloaded genhtml executable using http_file() in WORKSPACE, and then I created a custom bzl rule in which I incorporated a cmd command that runs that executable. (Being this was done so long ago, there are probably better ways to do things now) – Indebtedness

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

Dominy

Which bazel version are you using? – Epiboly

I tested with version 0.21.0 – Dominy

FWIW, your link is dead – Mcleroy

use bazel version 6.x to get the report .dat in $(bazel info output_path)/_coverage/_coverage_report.dat – Fare

Answer 3

For Java based project we can get code coverage in following way

To get coverage for complete module ->

1. 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

2. 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 ->

1. 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

2. 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

Savina