Fix section index partial NPE

[tobiaskohlbau]

During rendering the section index of a docs list it could happen that a file has no parent for e.g. the homepage. If such scenario is existing the .Parent.File of a file is nil. Therefore this case should be handled within the rendering itself.

Fixes #1874

[deining]

Just ran into the same issue, and the fix proposed with this PR solved my problem.
I realized that this contribution proposes a slight more elegant solution to the problem .
@tobiaskohlbau: can you have a look, please? Can we take over this solution here?

[tobiaskohlbau]

Just ran into the same issue, and the fix proposed with this PR solved my problem. I realized that this contribution proposes a slight more elegant solution to the problem . @tobiaskohlbau: can you have a look, please? Can we take over this solution here?

AFAIK the proposed solution would not work. As the and within the if only checks for the currently scoped Parent but not for every pages Parent.File.UniqueID. Therefore if pages do not have a Parent.File the access to UniqueID would throw a NPE. It's required to filter out all pages where Parent.File=nil. (IIRC I had such solution before and it still got said NPE.)

[yann-soubeyrand]

Hello,

I confirm what @tobiaskohlbau said.

Using Hugo 0.124.1, which contains the fix referred to above, on a docs only site, that is with the following front matter in content/_index.adoc

title: 'Documentation'
layout: 'section'

cascade:
 - type: 'docs'

I still get a warning:

WARN  .File.UniqueID on zero object. Wrap it in if or with: {{ with .File }}{{ .UniqueID }}{{ end }}

But the warning is solved when adding the modified partial from this PR.

[yann-soubeyrand]

I re-tested today and, in fact, this is not a warning, but an error:

ERROR render of "taxonomy" failed: "/home/yann/.cache/hugo/modules/filecache/modules/pkg/mod/github.com/camptocamp/docsy@v0.9.2-0.20240325160920-2e674ae180f3/layouts/docs/list.html:12:5": execute of template failed: template: docs/list.html:12:5: executing "main" at <partial "section-index.html" .>: error calling partial: "/home/yann/.cache/hugo/modules/filecache/modules/pkg/mod/github.com/camptocamp/docsy@v0.9.2-0.20240325160920-2e674ae180f3/layouts/partials/section-index.html:8:69": execute of template failed: template: partials/section-index.html:8:69: executing "partials/section-index.html" at <$parent.File.UniqueID>: error calling UniqueID: runtime error: invalid memory address or nil pointer dereference
Built in 3662 ms
Error: error building site: render: failed to render pages: render of "taxonomy" failed: "/home/yann/.cache/hugo/modules/filecache/modules/pkg/mod/github.com/camptocamp/docsy@v0.9.2-0.20240325160920-2e674ae180f3/layouts/docs/list.html:12:5": execute of template failed: template: docs/list.html:12:5: executing "main" – File is nil; wrap it in if or with: {{ with partial "section-index.html" .>: error calling partial: "/home/yann/.cache/hugo/modules/filecache/modules/pkg/mod/github.com/camptocamp/docsy@v0.9.2-0.20240325160920-2e674ae180f3/layouts/partials/section-index.html:8:69": execute of template failed: template: partials/section-index.html:8:69: executing "partials/section-index.html" at <.File }}{{ .UniqueID }}{{ end }}

I still confirm this PR fixes the issue.

[deining]

AFAIK the proposed solution would not work. As the and within the if only checks for the currently scoped Parent but not for every pages Parent.File.UniqueID. Therefore if pages do not have a Parent.File the access to UniqueID would throw a NPE. It's required to filter out all pages where Parent.File=nil. (IIRC I had such solution before and it still got said NPE.)

You are right. Your solution is more general and should be merged unchanged.

[chalin]

After looking at this more closely, it seems to make sense indeed.

Btw, the $parent variable is misnamed, because$parent is set to .Page.

Can we inline the variable instead?

Btw, IMHO .Page cannot be falsy, but .Page.File could be falsy. So the if condition can be simplified.

[chalin]

Will track separately:

• section-index.html: code cleanup #1946

[chalin]

I'm willing to give this a try.
RSLGTM based on appraisals by @deining and @yann-soubeyrand.
Thanks all! ✨