Introduce Nunjucks macros abstracting data attribute rendering

[romaricpascal]

What

Abstract rendering of data-attributes for passing configuration into a govukDataAttributes with a call of the following shape:

{{
	govukDataAttributes({
	   'attribute-name': value,
	   'other-attribute-name': {
		  value: otherValue, 
	      testUndefined: true,
	      escape: false # Only if there are instances we don't escape the attributes
	   }
	})
}}

Expand the concept with a helper for internationalisation attributes that relies on plurals or string key instead of value and delegates to govukDataAttributes, building the i18n.<attribute-name>[.plural-category] attribute name. Based on the ideas in this comment.

Why

Setting the attributes is very repetitive in the templates and always the same shape:

1. if {{value}} or {{value !== undefined}} to condition the rendering of the attribute itself
2. output " data-{{name}}="{{value | escape}}"

Who needs to work on this

Developers

Who needs to review this

Developers

Done when

• Abstraction macros have been introduced and tested
• Component templates have been updated to use the abstractions

[querkmachine]

I notice that an i18n related macro was added a couple of months ago, that seems related to this idea.

Is this issue still relevant or in need of updates in response to that?

[romaricpascal]

That macro is related to this idea indeed. It proposed to expand on it to set up a macro for rendering attributes in general, as we often do the same thing for rendering them: check if they're undefined, escape them...

Under the hood, the i18n macro would likely delegate to this generic macro for outputting its attribute, allowing it to focus on the bits specific to i18n (fishing the plural forms and formatting the attribute names).

The issue remains relevant I think. It doesn't need tackling urgently though (and is open to counter arguments if we think it's unhelpful 😊)

[colinrotherham]

Hadn't realised this issue existed. We nearly implemented this in:

• Simplify i18n macro to handle single or plural text #3867

Fairly quick to pull out another macro (for data- or regular attributes in general) from govukI18nAttributes()