Collection display template doesn't show related field

[Oreilles]

Preflight Checklist

• I have completed all Troubleshooting Steps.
• There's no other issue that already describes my problem.
• I'm on the latest version of Directus.

Describe the Bug

When setting a display template with relational fields for a collection, for exemple {{id}}, {{id_client.name}}, the related values used to show correctly. It is no longer the case, and any relational field now shows as --.

Maybe related to #7081 ?

To Reproduce

• Create two collections, one containing a relational column to the other
• Set collection A display template to something referencing some field of collection B
• Create and navigate to an item individual page to see the rendered template.

What version of Directus are you using?

9.0.0-rc.91

What version of Node.js are you using?

Official docker image default

What database are you using?

Postgres

What browser are you using?

Firefox

What operating system are you using?

macOS

How are you deploying Directus?

Docker

[Oreilles]

Strangely enough, #7628 seemed to have fixed the template rendering in the header bar, but not inside the layout. For exemple, in the map layout, the items pop-up on hover still showed false.

This is because of this:

directus/app/src/utils/render-string-template.ts

Lines 17 to 19 in 7a61da3

	for (const key in values) {
	if (typeof values[key] === 'object') values[key] = JSON.stringify(values[key]);
	}

Since all relational values are necessarily objects, they are stringified and then micromustache cannot render them as it cannot access the item props.