Make coverage reporting actually run, and send it to Codecov

.github/workflows/tests.yml

@@ -48,15 +48,18 @@ jobs:
           python_package_manager: "uv pip"
       - name: Run Tests
         run: hatch run cov:test
-      - uses: jupyterlab/maintainer-tools/.github/actions/upload-coverage@v1
-
-  coverage:
-    runs-on: ubuntu-latest
-    needs:
-      - tests
-    steps:
-      - uses: actions/checkout@v7
-      - uses: jupyterlab/maintainer-tools/.github/actions/report-coverage@v1
+      # Codecov merges the uploads of every matrix job into one report for
+      # the commit, so each job uploads its own and nothing combines them here.
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v5
+        with:
+          files: coverage.xml
+          disable_search: true
+          flags: ${{ matrix.os }}-${{ matrix.python-version }}
+          # Empty on pull requests from forks, where Codecov falls back to a
+          # tokenless upload. Flip fail_ci_if_error on once the secret is set.
+          token: ${{ secrets.CODECOV_TOKEN }}
+          fail_ci_if_error: false
 
   test_minimum_versions:
     name: Test Minimum Versions

.gitignore

@@ -17,6 +17,7 @@ __pycache__
 \#*#
 .#*
 .coverage
+coverage.xml
 .cache
 htmlcov
 docs/source/CHANGELOG.md

README.md

@@ -1,6 +1,7 @@
 # Traitlets
 
 [![Tests](https://github.com/ipython/traitlets/actions/workflows/tests.yml/badge.svg)](https://github.com/ipython/traitlets/actions/workflows/tests.yml)
+[![Coverage](https://codecov.io/gh/ipython/traitlets/branch/main/graph/badge.svg)](https://codecov.io/gh/ipython/traitlets)
 [![Documentation Status](https://readthedocs.org/projects/traitlets/badge/?version=latest)](https://traitlets.readthedocs.io/en/latest/?badge=latest)
 [![Tidelift](https://tidelift.com/subscription/pkg/pypi-traitlets)](https://tidelift.com/badges/package/pypi/traitlets)
 

codecov.yml

@@ -0,0 +1,45 @@
+# https://docs.codecov.com/docs/codecov-yaml
+codecov:
+  # Every job of the test matrix uploads its own report. Waiting for CI to
+  # finish keeps the comment and the statuses off a partial set of uploads,
+  # without pinning a build count that the matrix would drift away from.
+  require_ci_to_pass: true
+
+coverage:
+  precision: 2
+  round: down
+  range: "70...90"
+  status:
+    project:
+      default:
+        target: auto
+        # Don't fail a pull request over the rounding noise of a refactor
+        # that only moves code around.
+        threshold: 0.5%
+    patch:
+      default:
+        target: 80%
+        threshold: 5%
+
+# The test suite is measured alongside the library, so the overall number
+# blends the two. These components report on each separately: `traitlets` is
+# the one to watch, while `tests` mostly surfaces test code that never runs.
+component_management:
+  default_rules:
+    statuses:
+      - type: project
+        target: auto
+        threshold: 0.5%
+  individual_components:
+    - component_id: library
+      name: traitlets
+      paths:
+        - traitlets/**
+    - component_id: tests
+      name: tests
+      paths:
+        - tests/**
+
+comment:
+  layout: "condensed_header, components, condensed_files, condensed_footer"
+  require_changes: true

pyproject.toml

@@ -75,7 +75,7 @@ nowarn = "test -W default {args}"
 features = ["test"]
 dependencies = ["coverage[toml]", "pytest-cov"]
 [tool.hatch.envs.cov.scripts]
-test = "python -m pytest -vv --cov traitlets --cov-branch --cov-report term-missing:skip-covered {args}"
+test = "python -m pytest -vv --cov --cov-report term-missing:skip-covered --cov-report xml {args}"
 nowarn = "test -W default {args}"
 
 [tool.hatch.envs.typing]
@@ -174,8 +174,23 @@ exclude_lines = [
 ]
 
 [tool.coverage.run]
+branch = true
+# Keeps the paths in coverage.xml relative to the repository root, so that the
+# uploads from every matrix job line up with each other on Codecov.
 relative_files = true
-source = ["traitlets"]
+# The test suite is measured too, so that Codecov's `tests` component can
+# report on it: a test file with uncovered lines is a test that never runs.
+# Measuring from the repository root rather than listing the two directories
+# keeps the paths in coverage.xml distinct -- with `source = ["traitlets",
+# "tests"]` both config/__init__.py files are written out under the same name.
+source = ["."]
+omit = [
+  "docs/*",
+  "examples/*",
+  # mypy type-checks this file, pytest-mypy-testing never executes its bodies,
+  # so every line in it reads as uncovered. It is a fixture, not dead code.
+  "tests/test_typing.py",
+]
 
 [tool.repo-review]
 # traitlets publishes `traitlets[test]` / `traitlets[docs]` as documented