.TableOfContents ignores id's generated by heading render hook

[jmooring]

What version of Hugo are you using (hugo version)?

hugo v0.83.0-DEV+extended linux/amd64 BuildDate=unknown

Does this issue reproduce with the latest release?

Yes

Without a heading render hook

This markup:

## Section One

Produces this HTML:

<h2 id="section-one">Section One</h2>

With this item in the .TableOfContents:

<li><a href="#section-one">Section One</a></li>

At this point everything is behaving as expected.

With a heading render hook

layouts/_default/_markup/render-heading.html:

<h{{ .Level }} id="{{ printf "%s%s" "foo-" .Anchor | safeURL }}">{{ .Text | safeHTML }}</h{{ .Level }}>

Produces this HTML:

<h2 id="foo-section-one">Section One</h2>

With this item in the .TableOfContents:

<li><a href="#section-one">Section One</a></li>

The item in the .TableOfContents should be:

<li><a href="#foo-section-one">Section One</a></li>

[jmooring]

Example:

git clone --single-branch -b hugo-github-issue-8383 https://github.com/jmooring/hugo-testing hugo-github-issue-8383
cd hugo-github-issue-8383
hugo server

[matt9189]

It appears that the table of contents generation is dependent upon Goldmark's autoHeadingID being set to true. This parses the actual content in the markdown file to generate the link. In your example above, if you change "Section One" in the markdown file to "Hello Friend," the link would produce <a href="#hello-friend">.

Goldmark has a parser option that allows for custom ids if specified in the markdown file:
## heading {#id .className attrName=attrValue class="class1 class2"}

This can be added; however, it would not fix the issue above. The table of contents would have to be generated from parsing the html output rather than the markdown to incorporate the render hooks correctly. Or, at least that is what I have gathered from my investigation.

[bep]

This is certainly a known limitation. We could (and should?) maybe get by this if we allow setting attributes inside the hook, e.g.:

{{ $id := printf "%s%s" "foo-" .Anchor | safeURL }}
{{ .SetAttribute "id" $id }}
<h{{ .Level }} id="{{ $id }}">{{ .Text | safeHTML }}</h{{ .Level }}>