chore(go): route release notes through vociferate

internal/vociferate/vociferate.go

@@ -215,6 +215,11 @@ func UnreleasedBody(rootDir string, options Options) (string, error) {
 	return defaultService().UnreleasedBody(rootDir, options)
 }
 
+// ReleaseNotes returns the release section for a specific semantic version.
+func ReleaseNotes(rootDir, version string, options Options) (string, error) {
+	return defaultService().ReleaseNotes(rootDir, version, options)
+}
+
 // RecommendedTag returns the next semantic release tag based on current changelog state.
 func (s *Service) RecommendedTag(rootDir string, options Options) (string, error) {
 	resolved, err := resolveOptions(options)
@@ -281,6 +286,16 @@ func (s *Service) UnreleasedBody(rootDir string, options Options) (string, error
 	return s.readUnreleasedBody(rootDir, resolved.Changelog)
 }
 
+// ReleaseNotes returns the release section for a specific semantic version.
+func (s *Service) ReleaseNotes(rootDir, version string, options Options) (string, error) {
+	resolved, err := resolveOptions(options)
+	if err != nil {
+		return "", err
+	}
+
+	return s.readReleaseNotes(rootDir, strings.TrimPrefix(strings.TrimSpace(version), "v"), resolved.Changelog)
+}
+
 func sectionHasEntries(unreleasedBody, sectionName string) bool {
 	heading := "### " + sectionName
 	sectionStart := strings.Index(unreleasedBody, heading)
@@ -471,6 +486,10 @@ func readLatestChangelogVersion(rootDir, changelogPath string) (string, bool, er
 	return defaultService().readLatestChangelogVersion(rootDir, changelogPath)
 }
 
+func readReleaseNotes(rootDir, version, changelogPath string) (string, error) {
+	return defaultService().readReleaseNotes(rootDir, version, changelogPath)
+}
+
 func (s *Service) readLatestChangelogVersion(rootDir, changelogPath string) (string, bool, error) {
 	path := filepath.Join(rootDir, changelogPath)
 	contents, err := s.fileSystem.ReadFile(path)
@@ -485,6 +504,38 @@ func (s *Service) readLatestChangelogVersion(rootDir, changelogPath string) (str
 	return match[1], true, nil
 }
 
+func (s *Service) readReleaseNotes(rootDir, version, changelogPath string) (string, error) {
+	if version == "" {
+		return "", fmt.Errorf("release version must not be empty")
+	}
+
+	path := filepath.Join(rootDir, changelogPath)
+	contents, err := s.fileSystem.ReadFile(path)
+	if err != nil {
+		return "", fmt.Errorf("read changelog: %w", err)
+	}
+
+	text := string(contents)
+	headingExpr := regexp.MustCompile(`(?m)^## \[` + regexp.QuoteMeta(version) + `\](?:\([^\n)]*\))? - `)
+	headingLoc := headingExpr.FindStringIndex(text)
+	if headingLoc == nil {
+		return "", fmt.Errorf("release notes section for %s not found in changelog", version)
+	}
+
+	nextSectionRelative := strings.Index(text[headingLoc[0]+1:], "\n## [")
+	sectionEnd := len(text)
+	if nextSectionRelative != -1 {
+		sectionEnd = headingLoc[0] + 1 + nextSectionRelative
+	}
+
+	section := text[headingLoc[0]:sectionEnd]
+	if !strings.HasSuffix(section, "\n") {
+		section += "\n"
+	}
+
+	return section, nil
+}
+
 func deriveRepositoryURL(rootDir string) (string, bool) {
 	return defaultService().deriveRepositoryURL(rootDir)
 }