Top-level non-sectioning not converter is interpreted as empty sectioning helper

[rjgotten]

How often can you reproduce it?

• Always
• Sometimes
• Rarely
• Unable
• I didn’t try

Description:

When using an expression in stache that is supposed to render the result of a top-level not() call as a true or false string, e.g.
a basic aria-hidden="{{ not( this.expanded ) }}" as part of a disclosure widget, then the not converter will always render an empty string as a result.

The root cause is in broken logic in the not converter's getter:

can-stache/helpers/core.js

Lines 496 to 507 in 17b727a

	var notConverter = {
	get: function(obs, options){
	if(helpersCore.looksLikeOptions(options)) {
	return canReflect.getValue(obs) ? options.inverse() : options.fn();
	} else {
	return !canReflect.getValue(obs);
	}
	},
	set: function(newVal, obs){
	canReflect.setValue(obs, !newVal);
	}
	};

It uses looksLikeOptions and then falsely (!!) assumes whenever an options argument is present, that the not converter is being used as a {{#not}} sectioning helper. This leads to cases such as the above example to effectively be interpreted as:

aria-hidden="{{#not ( this.expanded ) }}{{/not}}"

- i.e. to be interpreted as never rendering any actual content, because the sectioning templates are empty.

Here's also a screenshot of the above problem in action, with the debugger halted on the problematic conditional branch:

What the converter should be doing is strengthening that check with an additional check of the options.isSection property.
E.g.

var notConverter = {
	get: function(obs, options){
		if(helpersCore.looksLikeOptions(options) && (options.isSection !== false)) {
			return canReflect.getValue(obs) ? options.inverse() : options.fn();
		} else {
			return !canReflect.getValue(obs);
		}
	},
	set: function(newVal, obs){
		canReflect.setValue(obs, !newVal);
	}
};

Steps to reproduce:

See the description.

Expected results:
The not converter handles the described case correctly and does not hit the sectioning helper logic branch.

Actual results:
The not converter handles the described case incorrectly and hits the sectioning helper logic branch.

Environment:

Software	Version
can-stache version	all current affected
Browser	any
Operating system	any