Decorators

[kpdecker]

This is intended for merging into master but also dependent on #1076 so PRing against that branch for discussion right now.

This implements inline partials in the form of:

{{#*inline "foo"}}bar{{/inline}}
{{> foo }}

Which exposes the foo template to the current block and all children. This also adds a special case for partial blocks to support template inheritance:

{{#> layout}}
  {{#*inline "content"}}bar{{/inline}}
{{/layout}}

Which exposes the content partial to the layout partial, allowing for overrides and other conditional behaviors.

This is implemented through the more generic decorators feature, which are loosely inspired by @wycats's javascript decorators proposal. These allow a declarative means to both annotate particular blocks with metadata as well as to wrap in behaviors when desired, prior to execution. In addition to the inline partial helper case, this allows for blocks to be flagged with metadata, using this example:

{{#grid data}}
  {{#*column "Column 1"}}{{foo}}{{/column}}
  {{#*column "Column 2"}}{{bar}}{{/column}}
{{/grid}}

Handlebars.registerDecorator('column', function(fn, props, container, options) {
  props.columns = props.columns || [];
  props.columns.push({key: options.args[0], body: options.fn});
});
Handlebars.registerHelper('grid', function(data, options) {
  var headers = options.fn.columns.map(function(column) { return column.key; }).join(',');
  return headers + '\n' + data.map(function(data) {
    return options.fn.columns.map(function(column) { return column.body(data); }).join(',');
  }).join('\n');
});

/cc @wycats, @mmun, @ErisDS

[kpdecker]

Released in 4.0.0