Automates CHANGELOG.md generation and draft release note management using Gemini AI, triggered on every GitHub Release event.

.github/release-drafter.yml

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+# Release Drafter configuration
+# ─────────────────────────────────────────────────────────────────────────────
+# Automatically drafts the GitHub Release body when PRs are merged to develop.
+# Uses PR labels to categorize changes. Works alongside the AI Changelog
+# Generator (changelog.yml) — release-drafter populates the GitHub Release UI,
+# while the changelog script writes the CHANGELOG.md file.
+#
+# Labels to apply on PRs:
+#   enhancement / feature  → 🚀 New Features
+#   bug / fix              → 🐛 Bug Fixes
+#   security               → 🔒 Security
+#   documentation / docs   → 📖 Documentation
+#   performance            → ⚡ Performance
+#   dependencies           → 📦 Dependency Updates
+#   breaking-change        → 💥 Breaking Changes
+
+name-template: '$RESOLVED_VERSION'
+tag-template:  '$RESOLVED_VERSION'
+
+# Match existing tag format: plain semver e.g. 1.8.1  (no "v" prefix)
+version-template: '$MAJOR.$MINOR.$PATCH'
+
+categories:
+  - title: '💥 Breaking Changes'
+    labels:
+      - 'breaking-change'
+  - title: '🚀 New Features'
+    labels:
+      - 'enhancement'
+      - 'feature'
+  - title: '🐛 Bug Fixes'
+    labels:
+      - 'bug'
+      - 'fix'
+  - title: '🔒 Security'
+    labels:
+      - 'security'
+  - title: '⚡ Performance'
+    labels:
+      - 'performance'
+  - title: '📖 Documentation'
+    labels:
+      - 'documentation'
+      - 'docs'
+  - title: '📦 Dependency Updates'
+    labels:
+      - 'dependencies'
+
+# How to format each change line
+change-template: '- $TITLE (#$NUMBER) @$AUTHOR'
+change-title-escapes: '\<*_&'
+
+# Which labels determine the next semantic version bump
+version-resolver:
+  major:
+    labels:
+      - 'breaking-change'
+      - 'major'
+  minor:
+    labels:
+      - 'enhancement'
+      - 'feature'
+      - 'minor'
+  patch:
+    labels:
+      - 'bug'
+      - 'fix'
+      - 'patch'
+      - 'security'
+      - 'performance'
+      - 'documentation'
+      - 'docs'
+      - 'dependencies'
+  default: patch
+
+# Template for the GitHub Release body
+template: |
+  ## What's Changed
+
+  $CHANGES
+
+  ---
+  📦 **Artifact:** `com.sap.cds:sdm:$RESOLVED_VERSION`
+  📖 **Full Changelog:** https://github.com/$OWNER/$REPOSITORY/blob/develop/CHANGELOG.md
+  🔗 **Compare:** https://github.com/$OWNER/$REPOSITORY/compare/$PREVIOUS_TAG...$RESOLVED_VERSION

.github/scripts/generate-changelog.js

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+/**
+ * AI Changelog Generator
+ * ─────────────────────────────────────────────────────────────────────────────
+ * Triggered by the changelog.yml workflow on every GitHub release event.
+ *
+ * What it does:
+ *  1. Finds the previous tag to determine the commit range
+ *  2. Fetches merged PRs and commit messages since the last tag
+ *  3. Calls Gemini to write a structured changelog entry matching the project's
+ *     existing CHANGELOG.md format (## Version / ### Added / ### Fixed …)
+ *  4. Prepends the generated entry to CHANGELOG.md
+ *  5. Git commit + push back to develop is handled by the workflow (not here)
+ *
+ * Required env vars: GITHUB_TOKEN, GEMINI_API_KEY, RELEASE_TAG
+ */
+
+'use strict';
+
+const { getOctokit, context } = require('@actions/github');
+const { GoogleGenerativeAI } = require('@google/generative-ai');
+const fs = require('fs');
+const path = require('path');
+
+// ─── Helpers ─────────────────────────────────────────────────────────────────
+
+function truncate(str, max) {
+    if (!str) return '';
+    return str.length <= max ? str : str.slice(0, max) + '...';
+}
+
+async function fetchWithRetry(fn, retries = 3, delay = 1000) {
+    for (let i = 0; i < retries; i++) {
+        try { return await fn(); }
+        catch (e) {
+            if (i === retries - 1 || (e.status && e.status < 500)) throw e;
+            console.warn(`Retry ${i + 1}/${retries} after error: ${e.message}`);
+            await new Promise(r => setTimeout(r, delay * Math.pow(2, i)));
+        }
+    }
+}
+
+// ─── Main ────────────────────────────────────────────────────────────────────
+
+async function run() {
+    const token      = process.env.GITHUB_TOKEN;
+    const apiKey     = process.env.GEMINI_API_KEY;
+    const currentTag = process.env.RELEASE_TAG;
+
+    if (!token)      throw new Error('GITHUB_TOKEN is required');
+    if (!currentTag) throw new Error('RELEASE_TAG is required');
+
+    const octokit        = getOctokit(token);
+    const { owner, repo } = context.repo;
+
+    console.log(`\n📋 Generating changelog for: ${owner}/${repo} @ ${currentTag}\n`);
+
+    // ─── 1. Find previous tag ────────────────────────────────────────────────
+    const tags = await fetchWithRetry(() =>
+        octokit.paginate(octokit.rest.repos.listTags, { owner, repo, per_page: 100 })
+    );
+
+    const currentIdx  = tags.findIndex(t => t.name === currentTag);
+    const previousTag = currentIdx >= 0 && tags[currentIdx + 1] ? tags[currentIdx + 1].name : null;
+
+    console.log(`🔖 Range: ${previousTag ?? '(beginning of repo)'} → ${currentTag}`);
+
+    // ─── 2. Get commits between tags ─────────────────────────────────────────
+    let commitMessages = [];
+    if (previousTag) {
+        try {
+            const { data } = await fetchWithRetry(() =>
+                octokit.rest.repos.compareCommits({ owner, repo, base: previousTag, head: currentTag })
+            );
+            commitMessages = data.commits
+                .map(c => c.commit.message.split('\n')[0].trim())
+                .filter(m =>
+                    m.length > 0 &&
+                    !m.startsWith('Merge ') &&
+                    !m.startsWith('Update version') &&
+                    !m.startsWith("docs(changelog):")
+                );
+            console.log(`📝 Found ${commitMessages.length} relevant commits`);
+        } catch (e) {
+            console.warn('⚠️  Could not compare commits:', e.message);
+        }
+    }
+
+    // ─── 3. Get merged PRs since previous tag ────────────────────────────────
+    let mergedPRs = [];
+    try {
+        // Resolve the date of the previous tag's commit for filtering PRs
+        let since = null;
+        if (previousTag) {
+            const refData = await fetchWithRetry(() =>
+                octokit.rest.git.getRef({ owner, repo, ref: `tags/${previousTag}` })
+            );
+            let sha = refData.data.object.sha;
+            // Annotated tags point to a tag object, not a commit directly
+            if (refData.data.object.type === 'tag') {
+                const tagObj = await fetchWithRetry(() =>
+                    octokit.rest.git.getTag({ owner, repo, tag_sha: sha })
+                );
+                sha = tagObj.data.object.sha;
+            }
+            const commitData = await fetchWithRetry(() =>
+                octokit.rest.repos.getCommit({ owner, repo, ref: sha })
+            );
+            since = commitData.data.commit.committer.date;
+            console.log(`📅 Looking for PRs merged after: ${since}`);
+        }
+
+        const allPRs = await fetchWithRetry(() =>
+            octokit.paginate(octokit.rest.pulls.list, {
+                owner, repo, state: 'closed', per_page: 100, sort: 'updated', direction: 'desc'
+            })
+        );
+
+        mergedPRs = allPRs
+            .filter(pr => {
+                if (!pr.merged_at) return false;
+                if (since && new Date(pr.merged_at) <= new Date(since)) return false;
+                return true;
+            })
+            .map(pr => ({
+                number: pr.number,
+                title:  pr.title,
+                labels: pr.labels.map(l => l.name),
+                body:   truncate(pr.body || '', 400),
+            }));
+
+        console.log(`🔀 Found ${mergedPRs.length} merged PRs`);
+    } catch (e) {
+        console.warn('⚠️  Could not fetch merged PRs:', e.message);
+    }
+
+    // ─── 4. Build Gemini prompt ───────────────────────────────────────────────
+    const prBlock = mergedPRs.length > 0
+        ? mergedPRs.map(pr =>
+            `- PR #${pr.number}: "${pr.title}" [labels: ${pr.labels.join(', ') || 'none'}]\n  Body: ${pr.body || '(none)'}`)
+          .join('\n')
+        : '(no PR data available — use commit messages)';
+
+    const commitBlock = commitMessages.length > 0
+        ? commitMessages.slice(0, 50).map(m => `- ${m}`).join('\n')
+        : '(no commit data available)';
+
+    const prompt = `You are a technical changelog writer for the SAP CAP Java SDK Document Management Service plugin.
+
+**Project context:**
+This is a Maven JAR library (Java 17) used by SAP CAP Java applications to route Attachment CRUD events to SAP Document Management Service via CMIS REST API. Key subsystems: CAP event handlers (@Before/@On/@After), OAuth2 token management (TokenHandler), EhCache 3 caching (8 named caches), Apache HttpClient 5 CMIS calls, multi-tenant Cloud Foundry deployments, upload virus scan states (uploading / Success / Failed / VirusDetected / VirusScanInprogress).
+
+**Version:** ${currentTag}
+
+**Merged PRs since previous release (${previousTag ?? 'beginning'}):**
+${prBlock}
+
+**Relevant commit messages:**
+${commitBlock}
+
+**Instructions — follow EXACTLY:**
+1. Output ONLY the changelog entry — no preamble, no explanation, no markdown fences.
+2. Match this exact format:
+
+## Version ${currentTag}
+
+### Added
+- <user-facing feature description>
+
+### Fixed
+- <user-facing bug fix description>
+
+3. Only include sections (Added / Fixed / Changed / Security / Deprecated) that have actual content — omit sections with nothing to report.
+4. Write each bullet as a clear, concise sentence a library consumer can understand. No internal class names.
+5. If a PR title or commit is vague, infer from the body or omit it entirely.
+6. Do NOT fabricate changes — only describe what is evidenced by the PR/commit data above.`;
+
+    // ─── 5. Call Gemini (with structured fallback) ────────────────────────────
+    let changelogEntry = '';
+
+    if (apiKey) {
+        try {
+            const genAI = new GoogleGenerativeAI(apiKey);
+            const model = genAI.getGenerativeModel({ model: 'gemini-2.5-flash' });
+            const result = await fetchWithRetry(() => model.generateContent(prompt));
+            changelogEntry = result.response.text().trim();
+            console.log('\n✅ Gemini generated changelog entry:\n');
+            console.log(changelogEntry);
+        } catch (e) {
+            console.warn(`⚠️  Gemini failed (${e.message}), falling back to structured list.`);
+        }
+    } else {
+        console.warn('⚠️  GEMINI_API_KEY not set — using structured fallback.');
+    }
+
+    // Structured fallback: build entry from PR labels without Gemini
+    if (!changelogEntry) {
+        const added   = mergedPRs.filter(pr => pr.labels.some(l => ['enhancement', 'feature'].includes(l)));
+        const fixed   = mergedPRs.filter(pr => pr.labels.some(l => ['bug', 'fix'].includes(l)));
+        const security = mergedPRs.filter(pr => pr.labels.includes('security'));
+        const other   = mergedPRs.filter(pr =>
+            !added.includes(pr) && !fixed.includes(pr) && !security.includes(pr) && pr.title
+        );
+
+        changelogEntry = `## Version ${currentTag}`;
+        if (added.length)    changelogEntry += `\n\n### Added\n${added.map(pr    => `- ${pr.title} (#${pr.number})`).join('\n')}`;
+        if (fixed.length)    changelogEntry += `\n\n### Fixed\n${fixed.map(pr    => `- ${pr.title} (#${pr.number})`).join('\n')}`;
+        if (security.length) changelogEntry += `\n\n### Security\n${security.map(pr => `- ${pr.title} (#${pr.number})`).join('\n')}`;
+        if (other.length)    changelogEntry += `\n\n### Changed\n${other.map(pr  => `- ${pr.title} (#${pr.number})`).join('\n')}`;
+
+        if (mergedPRs.length === 0 && commitMessages.length > 0) {
+            changelogEntry += `\n\n### Changed\n${commitMessages.slice(0, 15).map(m => `- ${m}`).join('\n')}`;
+        }
+
+        console.log('\n📋 Structured fallback entry:\n');
+        console.log(changelogEntry);
+    }
+
+    // ─── 6. Prepend entry to CHANGELOG.md ────────────────────────────────────
+    const changelogPath = path.join(process.cwd(), 'CHANGELOG.md');
+
+    if (!fs.existsSync(changelogPath)) {
+        throw new Error(`CHANGELOG.md not found at ${changelogPath}`);
+    }
+
+    const existing = fs.readFileSync(changelogPath, 'utf8');
+
+    // Guard: don't double-write if this version already exists
+    if (existing.includes(`## Version ${currentTag}`)) {
+        console.log(`\nℹ️  Version ${currentTag} already present in CHANGELOG.md — skipping write.`);
+        return;
+    }
+
+    // Insert after the header lines (everything before the first "## Version" block)
+    const firstVersionIdx = existing.indexOf('\n## Version');
+    let newContent;
+    if (firstVersionIdx !== -1) {
+        newContent =
+            existing.slice(0, firstVersionIdx + 1) +
+            '\n' + changelogEntry + '\n' +
+            existing.slice(firstVersionIdx + 1);
+    } else {
+        // No existing version entries — append after header
+        newContent = existing.trimEnd() + '\n\n' + changelogEntry + '\n';
+    }
+
+    fs.writeFileSync(changelogPath, newContent, 'utf8');
+    console.log('\n✅ CHANGELOG.md updated successfully.');
+}
+
+run().catch(err => {
+    console.error('❌ Changelog generation failed:', err.message);
+    process.exit(1);
+});