This allows us to avoid creating unnecessary AST nodes and avoids things like isHelper.
Side effect of these changes is that @data functions can now have data parameters passed to them.
Rather than keeping state in the AST, which requires some gymnastics, we create a separate visitor flow which does the top down iteration necessary to calculate all of the state needed for proper whitespace control evaluation.
This is a breaking change for string mode users as there is no longer a distinct type for data parameters. Instead data consumers should look for the @ prefix value.
Allows users to chain multiple helpers together using their inverse callbacks. I.e.
```
{{#if foo}}
{{else if bar}}
{{else}}
{{/if}}
```
The control flow here effectively causes the helpers to be nested. The above is actually syntactic sugar for this:
```
{{#if foo}}
{{else}}
{{#if bar}}
{{else}}
{{/if}}
{{/if}}
```
Any helper may be used in this manner, the only requirement is they support normal calls and inverse calls.
Introduces a breaking change in that `{{else foo}}` may no longer be used as a root level operator. Instead `{{^foo}}` must be used.
Fixes#72.
Handlebars now supports subexpressions.
{{foo (bar 3)}}
Subexpressions are always evaluated as helpers; if
`3` were omitted from the above example, `bar`
would be invoked as a param-less helper, even
though a top-levell `{{bar}}` would be considered
ambiguous.
The return value of a subexpression helper is
passed in as a parameter of a parent subexpression
helper, even in string params mode. Their type,
as listed in `options.types` or `options.hashTypes`
in string params mode, is "sexpr".
The main conceptual change in the Handlebars code
is that there is a new AST.SexprNode that manages
the params/hash passed into a mustache, as well
as the logic that governs whether that mustache
is a helper invocation, property lookup, etc.
MustacheNode, which used to manage this stuff,
still exists, but only manages things like
white-space stripping and whether the mustache
is escaped or not. So, a MustacheNode _has_
a SexprNode.
The introduction of subexpressions is fully
backwards compatible, but a few things needed
to change about the compiled output of a template
in order to support subexpressions. The main one
is that the options hash is no longer stashed in
a local `options` var before being passed to
either the helper being invoked or the
`helperMissing` fallback. Rather, the options
object is inlined in these cases. This does
mean compiled template sizes will be a little
bit larger, even those that don't make use of
subexpressions, but shouldn't have any noticeable
impact on performance when actually rendering
templates as only one of these inlined objects
will actually get evaluated.
kpdecker
Marcio Junior
Martin Muñoz
Jesse Ezell
machty
Stanley Stuart
Yehuda Katz
Les Hill