Render blocks in the parent context and assure a block is passed to templates that use @partial-block

[nyon]

We heavily use @partial-block in our project context. We noticed the following flaws with the current evaluation of partial-blocks in handlebars.java:

• If a partial provides a block, it is currently evaluated twice. We added an option to only lazy evaluate the partial to improve performance.
• Currently the implementation of @partial-block throws a stack overflow error (infinite recursion), when a block of a partial provides a template which also contains @partial-block (see example below). This is fixed by this pull request. Handlebars.js also supports this, see WIP: Possible fix for #1252: Using @partial-block twice in a template not possible handlebars-lang/handlebars.js#1290
• In order to protect against the case when a partial-block is required but not provided, we introduced the callee. It is used to check whether the last provided partial-block is the right partial block for the given call to {{> @partial-block}}.

stack overflow example:

{{!-- page.hbs --}}
{{#> special-button}}
  Lorem ipsum
{{/special-button}}

{{!-- special-button.hbs --}}
{{#> generic-button}}
  {{> @partial-block}}
{{/generic-button}}

{{!-- generic-button.hbs --}}
<button>
  {{> @partial-block}}
</button>

[coveralls]

Coverage increased (+0.04%) to 86.252% when pulling 94f37c0 on nyon:master into 1f6c48e on jknack:master.

[jknack]

Looks good, please add more of tests with lazyPartialBlockEvaluation = true

[jknack]

Let's add two examples when this flag is on/off

[nyon]

Hey I added two tests that deal with this pull request's changes. Is everything okay now?

[jknack]

remove empty line

[jknack]

This is something internal and it shouldn't be called callee. Let's create a name which is hard to override by users like Context. INVOCATION_STACK or/and by prefixing the class name: com.github.jknack.handlebars.internal.Partial.calle

[jknack]

please revert all the whitespace changes

[jknack]

Already merged it, but I'm struggling to figure out why we do fail here, can you explain?

Here is a test case that fails today bc of this check:

shouldCompileTo("{{#> dude x=23}}{{#> dude x=12}}{{/dude}}{{/dude}}",
        $("hash", $(), "partials",
            $("dude", "<div {{#if x}}x={{x}}{{/if}}>{{> @partial-block}}</div>")),
        "<div x=23><div x=12></div></div>");

[bjoern-dev]

Hi and thanks for the merge! We'll get back to you about this asap.