feat: add annotate-coverage action

[oleg-kozlyuk-grafana]

Summary

• Adds a new composite action annotate-coverage that highlights uncovered lines in a PR diff using Go coverage data. It parses Go coverage files from a directory, intersects them with a git diff, and emits text, Markdown, or GitHub Actions workflow commands (::notice file=...,line=...::...) that GitHub renders as PR annotations on the changed lines — no GitHub API client involved.
• The utility is lifted verbatim from https://github.com/oleg-kozlyuk-grafana/go-canopy
• Ships its own Go binary at cmd/annotate-coverage, with the existing canopy internal packages (coverage, diff, format, github, local) and their full test suites. Supports four diff modes: PR diff (base-ref + commit-sha), branch-vs-HEAD (base-ref), single-commit (commit-sha), and working-tree (no inputs).
• Wires the new action into release-please-config.json and .release-please-manifest.json with an initial version of 0.1.0, following the same pattern as actions/go-flaky-tests.

Test plan

• go test -race -short ./... passes inside actions/annotate-coverage/ (verified locally).
• go build ./cmd/annotate-coverage produces a working binary (verified locally; annotate-coverage version runs).
• prettier --check passes on action.yaml, README.md, and the release-please configs (verified locally).
• Try the action end-to-end on a downstream PR to confirm ::notice annotations appear in the GitHub UI on the expected lines.

🤖 Generated with Claude Code

[electron0zero]

lgtm.

[Copilot]

Pull request overview

This PR introduces a new composite GitHub Action (actions/annotate-coverage) backed by a Go CLI that parses Go coverage profiles, intersects them with a git diff, and emits results as text/Markdown or GitHub Actions annotation workflow commands. It also wires the action into release-please so it can be versioned and released like the other actions in this repo.

Changes:

• Added actions/annotate-coverage composite action + README with usage and inputs.
• Implemented Go CLI (cmd/annotate-coverage) and supporting internal packages for diff parsing, coverage parsing/merging, coverage-vs-diff analysis, and formatting.
• Updated release-please configuration/manifest to include actions/annotate-coverage starting at v0.1.0.

Reviewed changes

Copilot reviewed 32 out of 52 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
release-please-config.json	Adds release-please package entry for actions/annotate-coverage.
.release-please-manifest.json	Adds initial manifest version for actions/annotate-coverage.
actions/annotate-coverage/README.md	Documents action purpose, usage example, inputs, diff modes, and output formats.
actions/annotate-coverage/action.yaml	Defines composite action steps to build and run the Go binary with provided inputs.
actions/annotate-coverage/CHANGELOG.md	Initializes changelog for the new action.
actions/annotate-coverage/.gitignore	Ignores local build artifacts and coverage output while keeping fixtures tracked.
actions/annotate-coverage/go.mod	Declares the Go module and dependencies for the action implementation.
actions/annotate-coverage/go.sum	Locks Go dependency checksums for reproducible builds.
actions/annotate-coverage/cmd/annotate-coverage/main.go	Implements CLI entrypoint, flags, and diff-mode selection.
actions/annotate-coverage/internal/local/runner.go	Orchestrates diff acquisition, diff parsing, coverage loading/merging, analysis, and output.
actions/annotate-coverage/internal/local/runner_test.go	Adds tests around coverage loading/merging and runner behavior.
actions/annotate-coverage/internal/diff/diff.go	Defines the DiffSource abstraction.
actions/annotate-coverage/internal/diff/local.go	Implements working-tree diff acquisition (git add -N + git diff).
actions/annotate-coverage/internal/diff/local_test.go	Tests the local diff source using a temporary git repo.
actions/annotate-coverage/internal/diff/commit.go	Implements single-commit diff acquisition via git diff-tree.
actions/annotate-coverage/internal/diff/commit_test.go	Tests commit diff source behavior (valid/invalid SHAs, root commits).
actions/annotate-coverage/internal/diff/base.go	Implements base-vs-head diff acquisition via git diff base..commit.
actions/annotate-coverage/internal/diff/base_test.go	Tests base diff source behavior across SHAs and branch names.
actions/annotate-coverage/internal/coverage/parser.go	Parses Go coverage profiles (and coverage inside zip archives) into internal structures.
actions/annotate-coverage/internal/coverage/parser_test.go	Tests coverage parsing/validation and zip extraction behavior via fixtures.
actions/annotate-coverage/internal/coverage/merger.go	Merges multiple coverage profiles using a gocovmerge-style block merge.
actions/annotate-coverage/internal/coverage/merger_test.go	Tests merge behavior across modes, overlaps, and ordering.
actions/annotate-coverage/internal/coverage/diff.go	Parses unified diffs and extracts added line numbers per file (Go files only).
actions/annotate-coverage/internal/coverage/diff_test.go	Tests diff parsing across multiple scenarios (hunks, renames, deletions, binaries, etc.).
actions/annotate-coverage/internal/coverage/analysis.go	Computes uncovered added lines by intersecting coverage blocks with added diff lines; generates annotations.
actions/annotate-coverage/internal/coverage/analysis_test.go	Tests analysis logic, stats, comparisons, and annotation generation.
actions/annotate-coverage/internal/format/formatter.go	Factory for selecting output formatter by name.
actions/annotate-coverage/internal/format/text.go	Plain-text formatting of uncovered lines and summary coverage.
actions/annotate-coverage/internal/format/text_test.go	Tests text formatting and range compaction output.
actions/annotate-coverage/internal/format/markdown.go	Markdown table formatting of uncovered lines and summary coverage.
actions/annotate-coverage/internal/format/markdown_test.go	Tests Markdown formatting output.
actions/annotate-coverage/internal/format/github_annotations.go	Emits ::notice ...::... workflow commands for PR annotations.
actions/annotate-coverage/internal/format/github_annotations_test.go	Tests annotation command output formatting.
actions/annotate-coverage/internal/github/annotations.go	Sorts and groups line numbers into consecutive ranges.
actions/annotate-coverage/internal/github/annotations_test.go	Tests line grouping/sorting logic.
actions/annotate-coverage/testdata/diffs/simple_addition.diff	Diff fixture for simple additions.
actions/annotate-coverage/testdata/diffs/multiple_hunks.diff	Diff fixture for multiple hunks in one file.
actions/annotate-coverage/testdata/diffs/mixed_changes.diff	Diff fixture with additions and modifications.
actions/annotate-coverage/testdata/diffs/file_rename.diff	Diff fixture for renames.
actions/annotate-coverage/testdata/diffs/file_deletion.diff	Diff fixture for deletions.
actions/annotate-coverage/testdata/diffs/binary_file.diff	Diff fixture for binary changes.
actions/annotate-coverage/testdata/coverage/valid_single.out	Coverage fixture with multiple files/blocks.
actions/annotate-coverage/testdata/coverage/valid_count.out	Coverage fixture for count mode.
actions/annotate-coverage/testdata/coverage/valid_atomic.out	Coverage fixture for atomic mode.
actions/annotate-coverage/testdata/coverage/no_mode.out	Coverage fixture missing a mode header (parse failure).
actions/annotate-coverage/testdata/coverage/multiple_files_1.out	Coverage fixture used for merge tests (set mode).
actions/annotate-coverage/testdata/coverage/multiple_files_2.out	Additional coverage fixture used for merge tests.
actions/annotate-coverage/testdata/coverage/malformed.out	Malformed coverage fixture (parse failure).
actions/annotate-coverage/testdata/coverage/empty.out	Empty coverage fixture (parse failure).

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[Copilot]

Pull request overview

Copilot reviewed 34 out of 54 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

actions/annotate-coverage/internal/local/runner.go:1

• This unconditional stdout logging will intermix with formatter output. In GitHubAnnotations mode, it will add extra non-annotation lines to stdout, which can be noisy and makes the output harder to consume in pipelines. Prefer writing progress logs to stderr, gating behind a verbose flag, or removing this line.

[ricky-undeadcoders]

Nice work — clean structure and great test coverage. I ran it locally: go test -race -short ./... passes in all five packages, and the binary builds and runs fine. It follows the same pattern as go-flaky-tests, and building into RUNNER_TEMP keeps the user's checkout clean.

A couple of notes.

Should fix:

• internal/coverage/analysis.go:38 — matching a coverage file to a diff file by suffix is too loose. It can match the wrong file: a coverage profile for .../myhandler.go would match a diff entry for handler.go, because myhandler.go ends with handler.go. So coverage can get attributed to the wrong file.

  Line 41 already has the correct check (it requires a / right before the name, so handler.go only matches a real path segment). But that line never runs — line 38 matches everything line 41 would, and returns first. So the safe check is effectively dead code.

  Fix: drop the loose check on line 38 and keep the boundary one, plus an exact match for files at the repo root:

  if profileFile == diffFile || strings.HasSuffix(profileFile, "/"+diffFile) {
      return diffFile, addedLines, true
  }

  One more thing: this loops over a map, and Go map order is random. If two diff files both match, which one wins is nondeterministic. The fix above makes matches stricter, which helps, but worth keeping in mind.

Optional: E2E CI Test

test-annotate-coverage.yaml only runs go test. Some of the other test-* workflows in this repo also run the action itself and check its output — see test-component-change-detection.yml, which does uses: ./actions/component-change-detection and then validates the outputs. Right now nothing checks the action wiring end to end (inputs → command-line flags → the ::notice output GitHub renders). Adding this is good practice to future proof against regressions, but also to demonstrate that it currently works end-to-end.

It's a little more setup here, since the action computes the diff from live git state rather than taking a diff as input — so a meaningful test needs a small git repo plus a coverage file to intersect. If that's too much for this PR, a screenshot of annotations on a real downstream PR would at least confirm GitHub renders the output.

[oleg-kozlyuk-grafana]

Addressed the review comments, please take another look