Release scripts: extract CHANGELOG entries for the latest version to display in GitHub release notes

Author: yaroslav

spec/tasks/build_helpers/gem_publisher_spec.rb

@@ -148,4 +148,105 @@
       )
     end
   end
+
+  describe 'extracting a CHANGELOG part for the release notes' do
+    let(:changelog_content) do
+      <<~CHANGELOG
+        ## [Unreleased]
+
+        - Upcoming feature that is not yet released
+        - Another upcoming feature
+
+        ## [0.3.0] - 2026-01-29
+
+        - New `rake bun:install:package` task: automatically migrates `package.json` scripts
+        - New `rake bun:install:procfile` task: automatically migrates `Procfile` files
+        - Both tasks are automatically invoked by `rake bun:install`
+
+        ## [0.2.0] - 2025-01-30
+
+        - Major update with new features
+        - Breaking changes included
+
+        ## [0.1.0] - 2024-12-15
+
+        - Initial release
+      CHANGELOG
+    end
+
+    let(:tmpfile) do
+      file = Tempfile.new(['CHANGELOG', '.md'])
+      file.write(changelog_content)
+      file.close
+      file
+    end
+
+    after { tmpfile.unlink }
+
+    before do
+      allow(File).to receive(:expand_path)
+        .with('../../CHANGELOG.md', anything)
+        .and_return(tmpfile.path)
+    end
+
+    it 'extracts changelog content for a base version' do
+      result = publisher.send(:extract_changelog_for_version, '0.3.0')
+
+      expect(result).to include('rake bun:install:package')
+      expect(result).to include('rake bun:install:procfile')
+      expect(result).to include('Both tasks are automatically invoked')
+    end
+
+    it 'extracts changelog content for a composite version' do
+      result = publisher.send(:extract_changelog_for_version, '0.3.0.1.1.38')
+
+      expect(result).to include('rake bun:install:package')
+      expect(result).not_to include('Unreleased')
+      expect(result).not_to include('Major update')
+    end
+
+    it 'extracts the last version in changelog' do
+      result = publisher.send(:extract_changelog_for_version, '0.1.0')
+
+      expect(result).to eq('- Initial release')
+    end
+
+    it 'returns nil for non-existent version' do
+      result = publisher.send(:extract_changelog_for_version, '9.9.9')
+
+      expect(result).to be_nil
+    end
+
+    it 'does not include content from other versions' do
+      result = publisher.send(:extract_changelog_for_version, '0.2.0')
+
+      expect(result).to include('Major update')
+      expect(result).not_to include('Initial release')
+      expect(result).not_to include('rake bun:install:package')
+    end
+
+    context 'when changelog file does not exist' do
+      before do
+        allow(File).to receive(:expand_path)
+          .with('../../CHANGELOG.md', anything)
+          .and_return('/nonexistent/path/CHANGELOG.md')
+      end
+
+      it 'returns nil' do
+        result = publisher.send(:extract_changelog_for_version, '0.3.0')
+
+        expect(result).to be_nil
+      end
+    end
+
+    context 'when changelog has malformed content' do
+      let(:changelog_content) { 'This is not a valid changelog format' }
+
+      it 'returns nil' do
+        result = publisher.send(:extract_changelog_for_version, '0.3.0')
+
+        expect(result).to be_nil
+      end
+    end
+  end
 end

tasks/build_helpers/gem_publisher.rb

@@ -67,12 +67,24 @@ def upload_gem_files(release)
 
     def generate_release_notes
       bun_version = @version_checker.latest_bun_repo_version
-      <<~NOTES
+      changelog_content = extract_changelog_for_version(@version)
+
+      notes = <<~NOTES
         bundlebun #{@version}, includes a binary distribution of [Bun #{bun_version}](https://github.com/#{BuildHelpers::BUN_REPO}/releases/tag/bun-v#{bun_version}). Built for: #{PlatformManager::PLATFORM_MAPPING.keys.join(", ")}.
 
-        Changelog: [CHANGELOG](https://github.com/#{BuildHelpers::GEM_REPO}/blob/main/CHANGELOG.md).
+      NOTES
+
+      if changelog_content && !changelog_content.empty?
+        notes += <<~CHANGELOG
+          ### What's new
+
+          #{changelog_content}
+
+        CHANGELOG
+      end
 
-        See [README](https://github.com/#{BuildHelpers::GEM_REPO}) for installation instructions and documentation. See [LICENSE](https://github.com/#{BuildHelpers::GEM_REPO}/blob/main/LICENSE.txt) for licensing information.
+      notes += <<~FOOTER
+        See [README](https://github.com/#{BuildHelpers::GEM_REPO}) for installation instructions and documentation. See [CHANGELOG](https://github.com/#{BuildHelpers::GEM_REPO}/blob/main/CHANGELOG.md) for full history. See [LICENSE](https://github.com/#{BuildHelpers::GEM_REPO}/blob/main/LICENSE.txt) for licensing information.
 
         ### Quick installation
 
@@ -81,7 +93,24 @@ def generate_release_notes
 
         rake bun:install
         ```
-      NOTES
+      FOOTER
+
+      notes
+    end
+
+    def extract_changelog_for_version(version)
+      changelog_path = File.expand_path('../../CHANGELOG.md', __dir__)
+      base_version = version.to_s.split('.')[0..2].join('.')
+      content = File.read(changelog_path)
+
+      # Match the section for this version until the next version header or end of file
+      pattern = /^## \[#{Regexp.escape(base_version)}\][^\n]*\n(.*?)(?=^## \[|\z)/m
+      match = content.match(pattern)
+      return nil unless match
+
+      match[1].strip
+    rescue
+      nil
     end
 
     def publish_to_rubygems