Create additional references for duplicate footnotes

[facelessuser]

Track when we find duplicate footnote references and create unique ids
for them. Then add an additional tree-processor after inline to go
back and update the footnotes with additional back references that link
to the duplicate footnote references. Ref: #468.

[waylan]

Footnote 6 is repeated three times on the first line (once with id="fnref:a" and twice with id="fnref2:a".

Footnote 7 is repeated three times on the second line (once with id="fnref:a" and twice with id="fnref2:a".

However, in the actual footnotes below, we have three backreference links to each line line as:

footnote 6: href="#fnref:a", footnote 7: href="#fnref2:a" and footnote 8: href="#fnref3:a"
footnote 9: href="#fnref:a", footnote 10: href="#fnref2:a" and footnote 11: href="#fnref3:a"

We have two problems.

1. The footnote numbers don't match between the references and the backrefs. If we "jump back to footnote 8", then we should jump back to a footnote labeled "8" (i.e.; <sup>8</sup>)

2. There appears to be a bug in generating ids for the duplicates when there are more than two. Curiously, the backrefs point to the correct ids, but the references (after the first) are all assigned "fnref2:a" rather than counting up ("fnref2:a", "fnref3:a", ...).

[waylan]

Regarding problem 1 above, because the three references all point to the same footnote, they all should be labeled "6" (i.e.; <sup>6</sup>). So in this case, the bug is in the backrefs. All three should have identical tiles: "Jump back to footnote 6" (they do not), but point to different IDs (which they do).

[facelessuser]

"fnref2:a" rather than counting up ("fnref2:a", "fnref3:a", ...).

I missed that. I'll take a look.

[waylan]

So given the input in the test (repeated here in relevant part):

Duplicate[^a] footnotes[^a] test[^a].
 
Duplicate[^b] footnotes[^b] test[^b].
 
Single after duplicates[^c].

[^a]: 1
[^b]: 2
[^c]: 3

I would expect the following output:

<p>Duplicate<sup id="fnref:a"><a class="footnote-ref" href="#fn:a" rel="footnote">6</a></sup> footnotes<sup id="fnref2:a"><a class="footnote-ref" href="#fn:a" rel="footnote">6</a></sup> test<sup id="fnref3:a"><a class="footnote-ref" href="#fn:a" rel="footnote">6</a></sup>.</p>
<p>Duplicate<sup id="fnref:b"><a class="footnote-ref" href="#fn:b" rel="footnote">7</a></sup> footnotes<sup id="fnref2:b"><a class="footnote-ref" href="#fn:b" rel="footnote">7</a></sup> test<sup id="fnref3:b"><a class="footnote-ref" href="#fn:b" rel="footnote">7</a></sup>.</p>
<p>Single after duplicates<sup id="fnref:c"><a class="footnote-ref" href="#fn:c" rel="footnote">8</a></sup>.</p>

<div class="footnote">
<hr />
<ol>
<li id="fn:a">
<p>1&#160;<a class="footnote-backref" href="#fnref:a" rev="footnote" title="Jump back to footnote 6 in the text">&#8617;</a><a class="footnote-backref" href="#fnref2:a" rev="footnote" title="Jump back to footnote 6 in the text">&#8617;</a><a class="footnote-backref" href="#fnref3:a" rev="footnote" title="Jump back to footnote 6 in the text">&#8617;</a></p>
</li>
<li id="fn:b">
<p>2&#160;<a class="footnote-backref" href="#fnref:b" rev="footnote" title="Jump back to footnote 7 in the text">&#8617;</a><a class="footnote-backref" href="#fnref2:b" rev="footnote" title="Jump back to footnote 7 in the text">&#8617;</a><a class="footnote-backref" href="#fnref3:b" rev="footnote" title="Jump back to footnote 7 in the text">&#8617;</a></p>
</li>
<li id="fn:c">
<p>3&#160;<a class="footnote-backref" href="#fnref:c" rev="footnote" title="Jump back to footnote 8 in the text">&#8617;</a></p>
</li>
</ol>
</div>

[facelessuser]

The footnote numbers don't match between the references and the backrefs. If we "jump back to footnote 8", then we should jump back to a footnote labeled "8" (i.e.; ⁸)

I think I understand. I'll have both these resolved this evening.

[facelessuser]

I would expect the following output:

Excellent, that is what I was looking for.

I know what went wrong with issue 1 as I had iterated through multiple changes. While I track how many duplicates I have, I accidentally remove my tracker for unique ids.

Issue 2 is even easier. I just need to clone the first link and don't touch it's title and only update the link back.

[facelessuser]

These should be fixed now. Just force pushed the changes.