Implicit default block for embeds

[daun]

• New feature, closes make content of {embed} available #417
• BC break? no
• doc PR: happy to write one if you're on board with this feature :)

What this does

Provide an implicit default block for embeds and move any "loose" children into that default block.

Mirrors how other templating libraries deal with default/unnamed slots.

{* Pass button label into implicit `default` block *}

{embed button}
  Submit
{/embed}

Current state

Currently, I manually have to define the default block when embedding.

{define button}
  <button>
    {block default}Click{/block}
  </button>
{/define}

{embed button}
  {block default}
    Submit
  {/block}
{/embed}

It's a lot of noise when using many embeds.

<ul>
  <li>{embed button} {block default} Submit {/block} {/embed}</li>
  <li>{embed button} {block default} Reset {/block} {/embed}</li>
  <li>{embed button} {block default} Cancel {/block} {/embed}</li>
</ul>

With this feature

This will move any "loose" children into an implicit default block that the template file can render as necessary.

 {embed button}
-   {block default}
     Submit
-   {/block}
{/embed}

<ul>
  <li>{embed button}Submit{/embed}</li>
  <li>{embed button}Reset{/embed}</li>
  <li>{embed button}Cancel{/embed}</li>
</ul>

Explicit blocks and the implicit default block can live side by side.

{define button}
  <button>
    {block default}Click{/block}
    {block icon}<svg />{/block}
  </button>
{/define}

{embed button}
  Submit
  {block icon}<svg />{/block}
{/embed}

Explicit and implicit default block can never coexist and end up with a new compile error.

{* Throws: "Cannot combine loose content with an explicit {block default} inside {embed}"  *}

{embed button}
  Submit
  {block default}Send{/block}
{/embed}

Tests

Tests are added.

Nonbreaking

No existing tests have been modified.

Templates currently using a default block will keep working.

Also, this does not automatically render the loose content. Loose content is still ignored, just as before. It requires defining a {block default} inside the embedded content.

Alternative implementation

I was thinking of using an unnamed block instead of a default block. Not sure if that would've worked even? Also, I think default reads more intentional and in line with how most templating engines name their default slots.

{define button}
  <button>
    {block}Click{/block}
    {block icon}<svg />{/block}
  </button>
{/define}

[dg]

Thanks!

[jan-herman]

Great feature! I've been hoping for this for a while!

I've just noticed a small bug though. Using {include parent} results in the error "Cannot include undefined parent block 'content'."

[daun]

@jan-herman Interesting. It's probably best if you open a new issue on the repo, along with the exact latte template that triggers the error for you.

[dg]

@jan-herman fixed