fix(changelog): stage changelog file if necessary

internal/cmd/release.go

@@ -88,6 +88,14 @@ func (c Command) runRelease(dst io.Writer, l *flash.Logger, cfg config.Changelog
 			return err
 		}
 
+		if !g.IsStaged(*c.file) {
+			l.Debug("staging changelog", "file", *c.file)
+
+			if err := g.StageFile(*c.file); err != nil {
+				return err
+			}
+		}
+
 		l.Debug("committing changes")
 
 		if err := g.CommitFile(*c.file, fmt.Sprintf("chore: update changelog with %s release", version.String())); err != nil {

internal/git/git.go

@@ -96,6 +96,12 @@ func (c Command) HasRemotes() bool {
 	return err == nil
 }
 
+// IsStaged checks if a path is staged in repository.
+func (c Command) IsStaged(path string) bool {
+	_, err := c.Run("ls-files", "--error-unmatch", path)
+	return err == nil
+}
+
 // RevList runs git rev-list start..end
 func (c Command) RevList(start, end string) ([]string, error) {
 	arg := end