[chore] Automate changelog generation

.chloggen/summary.tmpl

@@ -12,22 +12,25 @@
 {{- end }}
 ## {{ .Version }}
 
-This release includes version XX.YY.ZZ of the upstream Collector components.
+<!-- upstream-start -->
+This release includes version <!-- upstream-version --> of the upstream Collector components.
 
 The individual upstream Collector changelogs can be found here:
 
-vXX.YY.ZZ:
+<!-- upstream-collector-versions -->
 
-- <https://github.com/open-telemetry/opentelemetry-collector/releases/tag/vXX.YY.ZZ>
-- <https://github.com/open-telemetry/opentelemetry-collector-contrib/releases/tag/vXX.YY.ZZ>
+<!-- upstream-breaking-changes -->
 
 <details>
 <summary>Highlights from the upstream Collector changelog</summary>
 
+<!-- upstream-other-changes -->
+
 ---
 
 </details>
 
+<!-- upstream-end -->
 {{- if or .BreakingChanges .Deprecations .NewComponents .BugFixes .Enhancements }}
 
 #### Dynatrace distribution changelog:

.github/workflows/upstream-changelog.yml

@@ -0,0 +1,73 @@
+name: Generate Changelog
+
+on:
+  workflow_dispatch:
+    inputs:
+      pr_urls:
+        description: >
+          Space-separated "prepare release" PR URLs (core and/or contrib).
+          Leave empty if there is no upstream release for this dist release.
+          Example: https://github.com/open-telemetry/opentelemetry-collector/pull/14515 https://github.com/open-telemetry/opentelemetry-collector-contrib/pull/45836
+        required: false
+        type: string
+      dist_version:
+        description: 'New dist version (e.g. 0.45.0 — leave empty to auto-bump minor)'
+        required: false
+        type: string
+
+env:
+  GO_VERSION: "1.25.7"
+
+jobs:
+  generate-changelog:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      pull-requests: write
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-go@v5
+        with:
+          go-version: ${{ env.GO_VERSION }}
+
+      - name: Bump dist.version in manifest.yaml and generate downstream changelog
+        run: |
+          if [ -n "${{ inputs.dist_version }}" ]; then
+            NEW_VERSION="${{ inputs.dist_version }}"
+          else
+            CURRENT=$(grep '  version:' manifest.yaml | head -1 | awk '{print $2}')
+            NEW_VERSION=$(echo "$CURRENT" | awk -F. '{printf "%d.%d.0", $1, $2+1}')
+          fi
+          sed -i "s/  version: .*/  version: $NEW_VERSION/" manifest.yaml
+          echo "DIST_VERSION=$NEW_VERSION" >> "$GITHUB_ENV"
+
+          make chlog-update VERSION="$NEW_VERSION"
+
+      - name: Build changelog generator
+        run: go build -o ./bin/changelog-generator ./internal/changelog-generator
+
+      - name: Fill upstream changelog placeholders
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          ./bin/changelog-generator ${{ inputs.pr_urls }}
+
+      - name: Create Pull Request
+        uses: peter-evans/create-pull-request@c0f553fe549906ede9cf27b5156039d195d2ece0 # v8.1.0
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          branch: changelog/v${{ env.DIST_VERSION }}
+          title: "[chore] Prepare release v${{ env.DIST_VERSION }}"
+          body: |
+            Auto-generated changelog for collector version v${{ env.DIST_VERSION }}.
+
+            **Source PRs:**
+            ${{ inputs.pr_urls != '' && inputs.pr_urls || '_No upstream release for this dist release._' }}
+
+            > ⚠️ Please review the generated changelog carefully before merging.
+            > The automation filters entries based on components in `manifest.yaml` and the allow/denylist in
+            > `internal/changelog-generator/config.yaml`. Some entries may need manual adjustment.
+          labels: Skip Changelog
+          commit-message: "chore: prepare release v${{ env.DIST_VERSION }}"
+

docs/releasing.md

@@ -21,13 +21,31 @@ Before starting a release, make a PR against to verify and update the following:
    Collector version. It is okay for bugfix versions to differ.
 3. Verify that no relevant bugs affecting the new versions were reported in the
    upstream Collector repositories.
-4. Ensure the `dist.version` key in `manifest.yaml` has the version of the
-   Dynatrace Collector you would like to release.
-5. Ensure the changelog has been generated by running `make chlog-update
-   VERSION="vX.X.X"` with your desired version.
-6. Update the upstream changelog links to the relevant upstream release.
-7. Look through the upstream release(s) and add any highlights to the
-   corresponding section(s).
+~~4. Ensure the `dist.version` key in `manifest.yaml` has the version of the
+   Dynatrace Collector you would like to release.~~
+~~5. Ensure the changelog has been generated by running `make chlog-update
+   VERSION="vX.X.X"` with your desired version.~~
+6. ~~Update the upstream changelog links to the relevant upstream release.~~
+7. ~~Look through the upstream release(s) and add any highlights to the
+   corresponding section(s).~~
+
+   **Steps 4–7 are now automated.** Run the
+   [Generate Upstream Changelog](../.github/workflows/upstream-changelog.yml)
+   workflow (`Actions → Generate Upstream Changelog → Run workflow`) with the
+   upstream "prepare release" PR URLs as input. The workflow will:
+   - Fetch the structured `.chloggen/*.yaml` entries from the upstream PRs
+   - Filter them to components present in `manifest.yaml` (plus the
+     allowlist in `internal/changelog-generator/config.yaml`)
+   - Insert the formatted upstream section into `CHANGELOG.md`
+   - Bump `dist.version` in `manifest.yaml` and `OTEL_UPSTREAM_VERSION` in
+     `Makefile`
+   - Open a PR for review
+
+   Review the generated PR carefully before merging — some entries may need
+   manual adjustment. See
+   [`internal/changelog-generator/README.md`](../internal/changelog-generator/README.md)
+   for details.
+
 8. Ensure all `go.mod` and `go.sum` files are up-to-date by running `make gotidy`
 
 ## Making a production release

internal/changelog-generator/.gitignore

@@ -0,0 +1,2 @@
+changelog-generator
+

internal/changelog-generator/README.md

@@ -0,0 +1,134 @@
+# changelog-generator
+
+A Go tool that fills the upstream changelog section in `CHANGELOG.md` during a release.
+
+`make chlog-update` (via `chloggen`) generates a new version section with placeholder comments.
+This tool fetches the upstream `.chloggen/*.yaml` entry files from the upstream "prepare release" PRs,
+filters them to components included in this distribution, and replaces those placeholders with real content.
+
+## Usage
+
+```sh
+# Upstream release: fill placeholders with content from the upstream PRs
+GITHUB_TOKEN=$(gh auth token) ./bin/changelog-generator \
+  https://github.com/open-telemetry/opentelemetry-collector/pull/14515 \
+  https://github.com/open-telemetry/opentelemetry-collector-contrib/pull/45836
+
+# Multi-version upgrade: pass all upstream PR URLs
+GITHUB_TOKEN=$(gh auth token) ./bin/changelog-generator \
+  https://github.com/open-telemetry/opentelemetry-collector/pull/14515 \
+  https://github.com/open-telemetry/opentelemetry-collector-contrib/pull/45836
+
+# Distro-only release (no upstream bump): removes the upstream placeholder section entirely
+GITHUB_TOKEN=$(gh auth token) ./bin/changelog-generator
+
+# Dry-run: print the generated pieces to stdout without modifying any files
+GITHUB_TOKEN=$(gh auth token) ./bin/changelog-generator -dry-run \
+  https://github.com/open-telemetry/opentelemetry-collector/pull/14515 \
+  https://github.com/open-telemetry/opentelemetry-collector-contrib/pull/45836
+```
+
+### Flags
+
+| Flag | Default | Description |
+|------|---------|-------------|
+| `-manifest` | `manifest.yaml` | Path to `manifest.yaml` |
+| `-config` | `internal/changelog-generator/config.yaml` | Path to allow/denylist config |
+| `-changelog` | `CHANGELOG.md` | Path to `CHANGELOG.md` |
+| `-dry-run` | `false` | Print to stdout without modifying files |
+
+## Building
+
+```sh
+go build -o ./bin/changelog-generator ./internal/changelog-generator
+```
+
+## How It Works
+
+1. **`make chlog-update VERSION="vX.Y.Z"`** runs `chloggen`, which consumes distro `.chloggen/*.yaml` entries and
+   writes a new version section into `CHANGELOG.md` using `summary.tmpl`. The template includes
+   named placeholder comments (`<!-- upstream-version -->`, `<!-- upstream-collector-versions -->`,
+   `<!-- upstream-breaking-changes -->`, `<!-- upstream-other-changes -->`) wrapped in
+   `<!-- upstream-start -->`/`<!-- upstream-end -->` boundary markers.
+
+2. **This tool** then fills those placeholders:
+   - Reads `manifest.yaml` to build the set of included upstream component IDs.
+   - For each supplied PR URL, fetches `.chloggen/*.yaml` files from the PR's **base commit** via
+     the GitHub Contents API (entries live at the base because the PR deletes them on merge), and
+     reads `versions.yaml` from the **head commit** to determine the upstream release version.
+   - Filters entries against the component set and the allow/denylist from `config.yaml`.
+   - Renders filtered entries into the four placeholder slots and removes the boundary markers.
+   - When no PR URLs are provided, removes the entire `<!-- upstream-start -->`…`<!-- upstream-end -->` block.
+
+## Configuration (`config.yaml`)
+
+```yaml
+# Always include entries for these component identifiers (exact or prefix match).
+allowlist:
+  - "pkg/ottl"
+  - "all"   # entries with component "all" affect every component
+
+# Always exclude. Denylist takes precedence over allowlist and manifest components.
+# Supports glob suffix (*) for prefix matching.
+denylist:
+  - "internal/*"
+  - "cmd/*"
+```
+
+- **To add a shared package**: add it to `allowlist` (e.g. `pkg/newpackage`).
+- **To suppress a component** even if it's in `manifest.yaml`: add it to `denylist`.
+
+## Component Name Mapping
+
+Component IDs are derived from `manifest.yaml` gomod paths:
+
+| `manifest.yaml` gomod | Upstream `component` ID |
+|---|---|
+| `go.opentelemetry.io/collector/receiver/otlpreceiver` | `receiver/otlp` |
+| `.../receiver/filelogreceiver` | `receiver/filelog` |
+| `.../processor/resourcedetectionprocessor` | `processor/resourcedetection` |
+| `.../extension/storage/filestorage` | `extension/filestorage` |
+
+The type suffix is stripped from the last path segment (e.g. `filelogreceiver` → `filelog`).
+
+## GitHub Actions Workflow
+
+The tool is wrapped by `.github/workflows/upstream-changelog.yml`, which:
+
+1. Runs `make chlog-update` to consume distro entries and write the scaffold.
+2. Runs this tool to fill the upstream placeholders.
+3. Bumps `dist.version` in `manifest.yaml` and `OTEL_UPSTREAM_VERSION` in `Makefile`.
+4. Opens a PR labelled `Skip Changelog` for human review.
+
+```
+Actions → "Generate Upstream Changelog" → Run workflow
+
+Inputs:
+  core_pr_url    (required)  upstream core "prepare release" PR URL
+  contrib_pr_url (required)  upstream contrib "prepare release" PR URL
+  extra_pr_urls  (optional)  comma-separated additional PR URLs for multi-version upgrades
+  dist_version   (optional)  e.g. 0.46.0 — auto-bumps minor version if omitted
+```
+
+## Running Tests
+
+```sh
+cd internal/changelog-generator
+go test ./...
+```
+
+## Troubleshooting
+
+**`GITHUB_TOKEN` not set / 403 errors**
+```sh
+export GITHUB_TOKEN=$(gh auth token)
+```
+
+**"no valid upstream versions found"**
+Each PR must have a `versions.yaml` at its head commit with a valid semver. The tool reads the
+version from `module-sets.beta.version` (core) or `module-sets.contrib-base.version` (contrib).
+
+**Entry not appearing in output**
+Run with `-dry-run` and check the `info:` lines on stderr. If a component is missing, add it to
+`allowlist` in `config.yaml`.
+

internal/changelog-generator/changelog.go

@@ -0,0 +1,83 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strings"
+)
+
+const (
+	upstreamStartMarker    = "<!-- upstream-start -->"
+	upstreamEndMarker      = "<!-- upstream-end -->"
+	upstreamVersionMarker  = "<!-- upstream-version -->"
+	upstreamVersionsMarker = "<!-- upstream-collector-versions -->"
+	upstreamBreakingMarker = "<!-- upstream-breaking-changes -->"
+	upstreamOtherMarker    = "<!-- upstream-other-changes -->"
+)
+
+// FillUpstreamPlaceholders reads the CHANGELOG.md at path and either fills the
+// upstream placeholder comments with content from UpstreamContent, or removes
+// the entire upstream section when UpstreamContent is zero-valued (no upstream
+// release).
+//
+// The expected scaffold (produced by `make chlog-update`) contains:
+//
+//	<!-- upstream-start -->
+//	This release includes version <!-- upstream-version --> ...
+//	<!-- upstream-collector-versions -->
+//	<!-- upstream-breaking-changes -->
+//	<details>
+//	<!-- upstream-other-changes -->
+//	</details>
+//	<!-- upstream-end -->
+//
+// After this function runs, the boundary markers are removed and only the
+// rendered content (or nothing) remains.
+func FillUpstreamPlaceholders(path string, content UpstreamContent) error {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return fmt.Errorf("reading changelog: %w", err)
+	}
+
+	s := string(data)
+
+	if content.VersionIntro == "" {
+		s = removeUpstreamSection(s)
+	} else {
+		s = strings.ReplaceAll(s, upstreamVersionMarker, content.VersionIntro)
+		s = fillOrRemovePlaceholder(s, upstreamVersionsMarker, content.CollectorVersions)
+		s = fillOrRemovePlaceholder(s, upstreamBreakingMarker, content.BreakingChanges)
+		s = fillOrRemovePlaceholder(s, upstreamOtherMarker, content.OtherChanges)
+		// Remove the boundary markers now that the content is in place.
+		s = strings.ReplaceAll(s, upstreamStartMarker+"\n", "")
+		s = strings.ReplaceAll(s, "\n\n"+upstreamEndMarker, "\n")
+	}
+
+	return os.WriteFile(path, []byte(s), 0o644)
+}
+
+// removeUpstreamSection removes everything between <!-- upstream-start --> and
+// <!-- upstream-end --> (both inclusive) and normalizes the surrounding
+// whitespace to a single blank line.
+func removeUpstreamSection(s string) string {
+	startIdx := strings.Index(s, upstreamStartMarker)
+	endIdx := strings.Index(s, upstreamEndMarker)
+	if startIdx == -1 || endIdx == -1 {
+		return s
+	}
+	endIdx += len(upstreamEndMarker)
+
+	before := strings.TrimRight(s[:startIdx], " \t\n")
+	after := strings.TrimLeft(s[endIdx:], " \t\n")
+	return before + "\n\n" + after
+}
+
+// fillOrRemovePlaceholder replaces a placeholder comment that lives on its own
+// line (surrounded by blank lines) with content. When content is empty the
+// placeholder line is removed entirely to avoid stray blank lines.
+func fillOrRemovePlaceholder(s, placeholder, content string) string {
+	if content == "" {
+		return strings.ReplaceAll(s, "\n\n"+placeholder+"\n", "\n")
+	}
+	return strings.ReplaceAll(s, placeholder, content)
+}