Duplicate footnotes have the problem of HTML ID collision conflict.

[yososs]

This problem can be reproduced with the following test case.

	@Test
	public void testDuplicatedFootnotes() {
		final MutableDataSet parseOptions = new MutableDataSet();
		parseOptions.set(Parser.EXTENSIONS, Arrays.asList(FootnoteExtension.create()));

		final MutableDataSet formatOptions = new MutableDataSet();
		formatOptions.set(Parser.EXTENSIONS, parseOptions.get(Parser.EXTENSIONS));

		final String markdownText = "Duplicated footnote reference[^id].\n\nreference[^id]\n\n[^id]: Footnote text.";
		final Parser parser = Parser.builder(parseOptions).build();

		final Node document = parser.parse(markdownText);

		final HtmlRenderer htmlRenderer = HtmlRenderer.builder(formatOptions).build();
		final String renderedHtml = htmlRenderer.render(document);

		System.out.println(renderedHtml);
		Assert.assertTrue(renderedHtml.indexOf("id=\"fn-1\"")==renderedHtml.lastIndexOf("id=\"fn-1\""));
		Assert.assertTrue(renderedHtml.indexOf("id=\"fnref-1\"")==renderedHtml.lastIndexOf("id=\"fnref-1\""));
	}

[vsch]

@yososs, here is what I am getting for sample markdown:

Duplicated footnote reference[^id].

reference[^id]

[^id]: Footnote text.

HTML:

<p>Duplicated footnote reference<sup id="fnref-1"><a class="footnote-ref" href="#fn-1">1</a></sup>.</p>
<p>reference<sup id="fnref-1"><a class="footnote-ref" href="#fn-1">1</a></sup></p>
<div class="footnotes">
  <hr />
  <ol>
    <li id="fn-1">
      <p>Footnote text.</p>
      <a href="#fnref-1" class="footnote-backref">&#8617;</a>
    </li>
  </ol>
</div>

Can you please let me know what you find wrong with the rendered HTML? I cannot see that it is wrong.

[yososs]

If there are multiple duplicate footnotes, the same ID is used twice in "fnref-1".

Using the same ID in HTML is not a serious problem with Web browsers, but if you use this HTML for EPUB content, EPUB Validator will detect it as an error.

Also, the jump from the footnote to the referring source is limited to one place.

In duplicate footnote, it might be to output such HTML.

<p>Duplicated footnote reference<sup id="fnref-1"><a class="footnote-ref" href="#fn-1">1</a></sup>.</p>
<p>reference<sup id="fnref-2"><a class="footnote-ref" href="#fn-1">1</a></sup></p>
<div class="footnotes">
  <hr />
  <ol>
    <li id="fn-1">
      <p>Footnote text.</p>
      <a href="#fnref-1" class="footnote-backref">&#8617;</a>
      <a href="#fnref-2" class="footnote-backref">&#8617;</a>
    </li>
  </ol>
</div>

Duplicated footnote reference¹.

reference¹

---

1. Footnote text.

   ↩ ↩

[vsch]

@yososs, the footnote extension now adds back references for each reference by adding a -# suffix for each reference except the first, where # is an integer from 1 to N

<p>Duplicated footnote reference<sup id="fnref-1"><a class="footnote-ref" href="#fn-1">1</a></sup>.</p>
<p>reference<sup id="fnref-1-1"><a class="footnote-ref" href="#fn-1">1</a></sup></p>
<div class="footnotes">
  <hr />
  <ol>
    <li id="fn-1">
      <p>Footnote text.</p>
      <a href="#fnref-1" class="footnote-backref">&#8617;</a>
      <a href="#fnref-1-1" class="footnote-backref">&#8617;</a>
    </li>
  </ol>
</div>

[vsch]

@yososs, repo updated. Maven update in progress, version 0.34.6