How do I make use of throw?

[Jieiku]

Documentation issue

The feature was merged here: Keats/tera#310

The documentation is here: https://keats.github.io/tera/docs/#throw

Summary

In the abridge theme when a user omits a required value in config.toml I would like to throw a specific error.

For instance the Abridge theme requires that compiles_sass is set to true, without it they see this error message:

Error: Failed to build the site
Error: Failed to render pager 1
Error: Reason: Failed to render 'index.html' (error happened in 'base.html').
Error: Reason: Function call 'get_url' failed
Error: Reason: `get_url`: Could not find or open file abridge.css

For a novice I think it would be best to explain exactly why they are seeing this error, which is that they simply need to set compiles_sass to true in config.toml

Here is what I have tried:

  {%- if config.compile_sass %}
    {%- set stylesheets=config.extra.stylesheets | default(value=[ "abridge.css" ]) -%}
    {%- if stylesheets %}{%- for i in stylesheets %}
      <link rel="stylesheet" href="{{     get_url(path=i                               , trailing_slash=false, cachebust=true) | safe }}" />
    {%- endfor %}{%- endif %}
  {%- else %}
    {% throw(message="Error: Theme requires that compile_sass is set to true in config.toml") %}
  {%- endif %}

but it does not seem to work, I get the following error:

zola serve

Building site...
Error: Failed to serve the site
Error: Error parsing templates from the /templates directory
Error: Reason: 
* Failed to parse "/home/jieiku/.dev/test/abridge/templates/partials/head.html"
  --> 25:5
   |
25 |     {% throw(message="Error: Theme requires that compile_sass is set to true in config.toml") %}
   |     ^---
   |
   = unexpected tag; expected an endif tag (`{% endif %}`) or some content

UPDATE: I just found another issue as well. It seems I cannot actually check the value of config.compile_sass from a template so I believe it is not exposed as a value you can check.

Proposed solution

I think it would be good to give a short example of how to use throw() on the tera or zola documentation sites.
I am guessing however that I did this correctly and it simply is not working anymore.
I really appreciate any help with this.

[welpo]

    {% throw(message="Error: Theme requires that compile_sass is set to true in config.toml") %}

throw is an expression, not a statement; you need to use {{ and }}, not {% and %}. This will work:

{{ throw(message="Error: Theme requires that compile_sass is set to true in config.toml") }}

I just found another issue as well. It seems I cannot actually check the value of config.compile_sass from a template so I believe it is not exposed as a value you can check.

I can't access it either (set to true, but ifs return false).

[Keats]

We are not passing the whole config, see https://github.com/getzola/zola/blob/master/components/config/src/config/mod.rs#L316-L335