feat: add changelog heading links for unreleased and releases

- Link Unreleased heading to repository main branch.
- Link release headings to release tag pages.
- Derive repository URL from CI metadata or origin git remote.
- Keep plain headings when repository URL cannot be resolved.
- Update tests and README usage docs for linked heading behavior.

internal/vociferate/vociferate.go

@@ -16,6 +16,9 @@ const (
 )
 
 var releasedSectionRe = regexp.MustCompile(`(?m)^## \[(\d+\.\d+\.\d+)\] - `)
+var linkedReleasedSectionRe = regexp.MustCompile(`(?m)^## \[(\d+\.\d+\.\d+)\](?:\([^\n)]*\))? - `)
+var unreleasedHeadingRe = regexp.MustCompile(`(?m)^## \[Unreleased\](?:\([^\n)]*\))?\n`)
+var releaseHeadingRe = regexp.MustCompile(`(?m)^## \[(\d+\.\d+\.\d+)\](?:\([^\n)]*\))? - `)
 
 type Options struct {
 	VersionFile    string
@@ -202,6 +205,10 @@ func updateChangelog(rootDir, version, releaseDate, changelogPath string) error
 	}
 
 	updated := text[:afterHeader] + "\n" + newSection + text[nextSectionStart:]
+	repoURL, ok := deriveRepositoryURL(rootDir)
+	if ok {
+		updated = addChangelogLinks(updated, repoURL)
+	}
 	if err := os.WriteFile(path, []byte(updated), 0o644); err != nil {
 		return fmt.Errorf("write changelog: %w", err)
 	}
@@ -245,13 +252,12 @@ func readChangelogState(rootDir, changelogPath string) (string, string, int, int
 	}
 
 	text := string(contents)
-	unreleasedHeader := "## [Unreleased]\n"
-	start := strings.Index(text, unreleasedHeader)
-	if start == -1 {
+	headerLoc := unreleasedHeadingRe.FindStringIndex(text)
+	if headerLoc == nil {
 		return "", "", 0, 0, "", fmt.Errorf("unreleased section not found in changelog")
 	}
 
-	afterHeader := start + len(unreleasedHeader)
+	afterHeader := headerLoc[1]
 	nextSectionRelative := strings.Index(text[afterHeader:], "\n## [")
 	if nextSectionRelative == -1 {
 		nextSectionRelative = len(text[afterHeader:])
@@ -269,13 +275,127 @@ func readLatestChangelogVersion(rootDir, changelogPath string) (string, bool, er
 		return "", false, fmt.Errorf("read changelog: %w", err)
 	}
 
-	match := releasedSectionRe.FindStringSubmatch(string(contents))
+	match := linkedReleasedSectionRe.FindStringSubmatch(string(contents))
 	if match == nil {
 		return "", false, nil
 	}
 	return match[1], true, nil
 }
 
+func deriveRepositoryURL(rootDir string) (string, bool) {
+	serverURL := strings.TrimSpace(os.Getenv("GITHUB_SERVER_URL"))
+	repository := strings.TrimSpace(os.Getenv("GITHUB_REPOSITORY"))
+	if serverURL != "" && repository != "" {
+		return strings.TrimSuffix(serverURL, "/") + "/" + strings.TrimPrefix(repository, "/"), true
+	}
+
+	gitConfigPath := filepath.Join(rootDir, ".git", "config")
+	contents, err := os.ReadFile(gitConfigPath)
+	if err != nil {
+		return "", false
+	}
+
+	remoteURL, ok := originRemoteURLFromGitConfig(string(contents))
+	if !ok {
+		return "", false
+	}
+
+	repoURL, ok := normalizeRepoURL(remoteURL)
+	if !ok {
+		return "", false
+	}
+
+	return repoURL, true
+}
+
+func originRemoteURLFromGitConfig(config string) (string, bool) {
+	inOrigin := false
+	for _, line := range strings.Split(config, "\n") {
+		trimmed := strings.TrimSpace(line)
+		if strings.HasPrefix(trimmed, "[") && strings.HasSuffix(trimmed, "]") {
+			inOrigin = trimmed == `[remote "origin"]`
+			continue
+		}
+
+		if !inOrigin {
+			continue
+		}
+
+		if strings.HasPrefix(trimmed, "url") {
+			parts := strings.SplitN(trimmed, "=", 2)
+			if len(parts) != 2 {
+				continue
+			}
+			url := strings.TrimSpace(parts[1])
+			if url != "" {
+				return url, true
+			}
+		}
+	}
+
+	return "", false
+}
+
+func normalizeRepoURL(remoteURL string) (string, bool) {
+	remoteURL = strings.TrimSpace(remoteURL)
+	if remoteURL == "" {
+		return "", false
+	}
+
+	if strings.HasPrefix(remoteURL, "http://") || strings.HasPrefix(remoteURL, "https://") {
+		return strings.TrimSuffix(remoteURL, ".git"), true
+	}
+
+	if strings.HasPrefix(remoteURL, "ssh://") {
+		withoutScheme := strings.TrimPrefix(remoteURL, "ssh://")
+		at := strings.Index(withoutScheme, "@")
+		if at == -1 {
+			return "", false
+		}
+		hostAndPath := withoutScheme[at+1:]
+		host, path, ok := strings.Cut(hostAndPath, "/")
+		if !ok || host == "" || path == "" {
+			return "", false
+		}
+		return "https://" + host + "/" + strings.TrimSuffix(path, ".git"), true
+	}
+
+	if strings.Contains(remoteURL, "@") && strings.Contains(remoteURL, ":") {
+		afterAt, ok := strings.CutPrefix(remoteURL, strings.Split(remoteURL, "@")[0]+"@")
+		if !ok {
+			return "", false
+		}
+		host, path, ok := strings.Cut(afterAt, ":")
+		if !ok || host == "" || path == "" {
+			return "", false
+		}
+		return "https://" + host + "/" + strings.TrimSuffix(path, ".git"), true
+	}
+
+	return "", false
+}
+
+func addChangelogLinks(text, repoURL string) string {
+	repoURL = strings.TrimSuffix(strings.TrimSpace(repoURL), "/")
+	if repoURL == "" {
+		return text
+	}
+
+	mainURL := repoURL + "/src/branch/main"
+	text = unreleasedHeadingRe.ReplaceAllString(text, fmt.Sprintf("## [Unreleased](%s)\n", mainURL))
+
+	text = releaseHeadingRe.ReplaceAllStringFunc(text, func(match string) string {
+		parts := releaseHeadingRe.FindStringSubmatch(match)
+		if len(parts) < 2 {
+			return match
+		}
+		version := parts[1]
+		return fmt.Sprintf("## [%s](%s/releases/tag/v%s) - ", version, repoURL, version)
+	})
+
+	return text
+}
+
 func parseSemver(version string) (semver, error) {
 	parts := strings.Split(strings.TrimSpace(version), ".")
 	if len(parts) != 3 {