Duplicated "DON'T EDIT THIS SECTION" lines in README since v2.4.0

[okuryu]

After upgrading to doctoc v2.4.0, the "DON'T EDIT THIS SECTION" header lines are being duplicated every time I run the command. This behavior does not occur in v2.3.0.

Steps to repro

README.md:

# H1

<!-- START doctoc generated TOC please keep comment here to allow auto update -->
<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->

- [H2-1](#h2-1)
- [H2-2](#h2-2)
- [H2-3](#h2-3)

<!-- END doctoc generated TOC please keep comment here to allow auto update -->

## H2-1

## H2-2

## H2-3

Run the latest doctoc:

npx doctoc@latest README.md --github

Observe that the "DON'T EDIT THIS SECTION" lines are added repeatedly instead of being updated in place.

diff --git a/README.md b/README.md
index 7ddf7a5..f1c9330 100644
--- a/README.md
+++ b/README.md
@@ -2,6 +2,7 @@
 
 <!-- START doctoc generated TOC please keep comment here to allow auto update -->
 <!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
+<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
 
 - [H2-1](#h2-1)
 - [H2-2](#h2-2)

Expected behavior

The TOC should be updated without duplicating the warning headers, consistent with the behavior in v2.3.0.

Additional context

Version 2.3.0: Works as expected (no duplication).

Version 2.4.0: Causes duplication.

Is this an intended breaking change? Also, is there a new option available in v2.4.0 to maintain the previous behavior?

[thompson-tomo]

@okuryu I will take a look at it in the coming days. Can you ensure that when you run the update command you are calling it with the --notitle argument and let us know if that works around it.

[okuryu]

Yup, it looks like adding --notitle option will make it behave the same as before.

[potiuk]

Hitting this in apache/airflow#65221 as well after bumping to v2.4.0.

For anyone else tracking this down, here's the root cause:

fc67456 (Allow control of Header and Footer, #316) rewrote determineTitle in lib/transform.js:

function determineTitle(title, notitle, lines, info) {
  var defaultTitle = '**Table of Contents**  *generated with [DocToc](https://github.com/thlorenz/doctoc)*';

  if (notitle) return "";
  if (title) return title;
  if (!info.hasStart) return defaultTitle;
  var readTitle = lines[info.startIdx + 2];
  var previousLine = lines[info.startIdx + 1];
  return readTitle != "" || previousLine.includes("END doctoc") ? readTitle : previousLine;
}

For the perfectly ordinary pattern

<!-- START doctoc generated TOC please keep comment here to allow auto update -->   ← startIdx
<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->                    ← startIdx + 1
                                                                                      ← startIdx + 2 (empty)
- [H2-1](#h2-1)

readTitle is "", previousLine is the <!-- DON'T EDIT ... --> comment, and neither readTitle != "" nor previousLine.includes("END doctoc") is true — so the function returns previousLine, treating the DON'T EDIT comment as the title.

Then transform emits start + '\n' + toc + '\n' + end, where start (from legacyPragma) is already two lines including the DON'T EDIT comment, and toc starts with that same comment as inferredTitle. Net result: the DON'T EDIT line is written twice on every run.

A minimal fix would be to treat an empty readTitle as "no title" directly, or at least to also skip lines matching previousLine.includes("doctoc") / the other doctoc pragma markers — not only END doctoc. Happy to open a PR if that direction sounds right.

In the meantime, confirming --notitle works as a workaround for Airflow as well.

[thompson-tomo]

Unfortunately I don't think that will work, especially as I have already improved robustness of the troublesome determineTitle but not enough to cater for this use case. I have raised #341 to address the regression

[AndrewSouthpaw]

A fix is released in v2.4.1. Thanks for your patience @potiuk, @okuryu! Thanks to @thompson-tomo for the quick fix.