glcov

Line coverage and a profiler for Gleam projects, with Erlang and JavaScript backends.

glcov is for Gleam teams that want a coverage table, coverage/lcov.info, and a CI gate without changing test files. It covers direct path dependencies and profiles test suites at function level.

Quick start

gleam add --dev glcov
gleam run --target erlang -m glcov -- run

The default backend builds the project, runs its EUnit or gleeunit tests under Erlang cover, and maps counted lines back to .gleam files.

2 passed, no failures
File                       Lines   Covered   Uncovered        %
src/fixture_basic.gleam        5         3           2    60.00
TOTAL                          5         3           2    60.00

Coverage: 60.00% (3/5 lines covered)
Wrote coverage/lcov.info

The gleam CLI has no plugin system, so gleam coverage is not a command. glcov installs as a dev dependency and runs as a module.

CI

- uses: erlef/setup-beam@v1
  with:
    otp-version: "28"
    gleam-version: "1.19.2"
- run: gleam deps download
- run: gleam run --target erlang -m glcov -- run --min 85
- uses: codecov/codecov-action@v5
  with:
    files: coverage/lcov.info

Other backends and modes

JavaScript: gleam run --target erlang -m glcov -- run --target javascript. Requires c8 and [javascript] source_maps = true.
Path dependencies: direct runtime path dependencies in gleam.toml are included automatically. Use --include-dep <PATH> for dev dependencies or undeclared packages, and --no-path-deps to opt out.
Self time: gleam run --target erlang -m glcov -- prof test --mode self_time.
Escript: build with bash scripts/build_escript.sh and run ./glcov.escript run for stateful applications.
Nix: nix build .#glcov, then run ./result/bin/glcov run.

Real-project checks

These public projects were run against glcov with their own test suites:

Project	Tests	Line coverage	Notes
`gleeunit`	25 passed	9.43%	Most tests target JavaScript, so the low coverage is expected.
`gleam_stdlib`	1548 passed	80.05%
`wisp`	164 passed	86.44%	Fresh build with the escript; uses `gleam_stdlib` 0.70.

The wisp run checks the older stdlib path. The other runs use their current dependencies.

Documentation

Requirements

The Erlang backend needs Gleam 1.19 or newer, Erlang/OTP 26 or newer, and gleam_stdlib 0.70 or newer. The JavaScript backend needs Node and c8 on PATH, plus [javascript] source_maps = true. The call_time and call_count profiler modes need OTP 27; self_time needs OTP 26.

Licence

Apache-2.0. See LICENCE.