Support stacked PRs for subfeatures

lib/sugarjar/commands.rb

@@ -330,9 +330,9 @@ def smartpullrequest(*args)
       end
 
       if gh?
+        curr = current_branch
+        base = tracked_branch
         if @pr_autofill
-          curr = current_branch
-          base = tracked_branch
           num_commits = git(
             'rev-list', '--count', curr, "^#{base}"
           ).stdout.strip.to_i
@@ -345,6 +345,14 @@ def smartpullrequest(*args)
             args.unshift('--fill')
           end
         end
+        if all_local_branches.reject { |x| x == most_main }.include?(base)
+          $stdout.print(
+            'It looks like this is a subfeature, would you like to base ' +
+            "this PR on #{base}? [y/n] ",
+          )
+          ans = $stdin.gets.strip
+          args += ['--base', base] if %w{Y y}.include?(ans)
+        end
         SugarJar::Log.trace("Running: gh pr create #{args.join(' ')}")
         system(which('gh'), 'pr', 'create', *args)
       else