Feature: Pass variables to layouts

[mzeinstra]

It might be interesting to allow passing variables to layouts to make layouts more flexible and self contained.

e.g. I want to get references from a statement on Wikibase and want to print it in something like:

<h2>{{ .title }}</h2>
<p>reference 1</p>
<p>reference 2</p>

I would now do:

<h1>{{ .title }}</h1>
{{ $data := query "references_by_statement.rq" .linkToStatement }}
{{ template "references" $data }}

with the template for "references" being

{{ if . }}
	{{ range . }}
	<p>{{ .text }}</p>
	{{ end }}
{{ end }}

Instead it would be interesting to reserve pass the title to the layout so that the H1 can be part of the layout. i.e.

{{ $data := query "references_by_statement.rq" .linkToStatement}}
{{ template "references" $data .title }}

{{ if . }}
	<h1>{{ .$0 }}</h1>
	{{ range . }}
	<p>{{ .text }}</p>
	{{ end }}
{{ end }}

Because sometimes you want to use that overarching information in your css or js to make the site more interactive.

With this structure we could allow passing up to 9 variables to the layout.

[Abbe98]

How does this idea compare to using multiply block definitions in a layout?

[mzeinstra]

I see I made a typo. I wanted to do this:

{{ $data := query "references_by_statement.rq" .linkToStatement}}
{{ template "references" $data .title }}

how would you do this in multiple blocks? Maybe my understanding of blocks and scoping is insufficient.

[Abbe98]

As of right now template can take a variable as input, the common pattern is to pass . to it, for it to inherit the global set of view-variables. With #37 it would be trivial to modify it and thus achieve the same outcome as using multiple variables, however, I would imagine such a use being a code-smell, as having local computation modify layout behavior outside of blocks is a type of side-effect.

It would be interesting to see what downsides there are with the following pattern using blocks:

layouts/base.html

<h1>{{ block "title" . }}{{ end }}</h1>
{{ block "references" . }}{{ end }}

my-template.html

{{ template "base" . }}
{{ define "title" }}{{ .title }}{{ end }}

{{ $data := query "references_by_statement.rq" .linkToStatement }}
{{ define "references"}}
  {{ range $data }}
    <p>{{ .text }}</p>
  {{ end }}
{{ end }}

There is also include/include_text for working with non-layout templating as well as current_view which is commonly used in layouts to manage things like JavaScript and CSS resources.

Notably include/include_text only supports one argument as well but that should be fixed as passing data to a child template is not an issue. #79