Cache count of 0 with templates.Defer

[tifenak]

hugo --templateMetrics --templateMetricsHints reports a cache count of 0 with Tailwind CSS template.Defer and partialCached. Is this expected?

[jmooring]

The “key” to understanding this is the key option passed to the templates.Defer function:

The key to use for the deferred template. This will, combined with a hash of the template content, be used as a cache key. If this is not set, Hugo will execute the deferred template on every render. This is not what you want for shared resources like CSS and JavaScript.

By way of example…

site configuration

disableKinds = ['home','rss','section','sitemap','taxonomy','term']

project structure

content/
├── p1.md
├── p2.md
└── p3.md
layouts/
├── _partials/
│   ├── defer-no-cache-no.html
│   ├── defer-no-cache-yes.html
│   ├── defer-yes-cache-no.html
│   └── defer-yes-cache-yes.html
└── page.html

layouts/page.html

{{ partial "defer-no-cache-no.html" . }}
{{ partialCached "defer-no-cache-yes.html" . }}
{{ with (templates.Defer (dict "key" "global")) }} <-- the key is static
  {{ partial "defer-yes-cache-no.html" . }}
  {{ partialCached "defer-yes-cache-yes.html" . }}
{{ end }}

hugo --templateMetrics --templateMetricsHints

    cache  percent  cached  total  
potential   cached   count  count  template
---------  -------  ------  -----  --------
        0        0       0      3  page.html
        0        0       0      1  __hdeferred/6d7359a18dad0569
      100        0       0      3  _partials/defer-no-cache-no.html
      100       67       2      3  _partials/defer-no-cache-yes.html
      100        0       0      1  _partials/defer-yes-cache-no.html
      100        0       0      1  _partials/defer-yes-cache-yes.html    

Note that the two deferred templates (the last two on the list) are run only once.

If we omit the key to the templates.Defer function:

hugo --templateMetrics --templateMetricsHints

    cache  percent  cached  total  
potential   cached   count  count  template
---------  -------  ------  -----  --------
        0        0       0      3  __hdeferred/6d7359a18dad0569
        0        0       0      3  page.html
      100        0       0      3  _partials/defer-no-cache-no.html
      100       67       2      3  _partials/defer-yes-cache-yes.html
      100        0       0      3  _partials/defer-yes-cache-no.html
      100       67       2      3  _partials/defer-no-cache-yes.html

---

Test site:

git clone --single-branch -b hugo-forum-topic-56069 https://github.com/jmooring/hugo-testing hugo-forum-topic-56069
cd hugo-forum-topic-56069
hugo --templateMetrics --templateMetricsHints