Fix for #2274

[mklauber]

List fields (such as tags) when evaluated to produce tiddlers result in empty arrays. Using the exact not equals, an empty array is not the same as an empty string. By using equivelent not equals, we state that the field is either != "" or anything that can be coerced to "". Which, based on https://dorey.github.io/JavaScript-Equality-Table/ is false 0 [] or [[]] neither false nor 0 can be set as a tiddler field as both will end up being quoted ("false", "0") so this should work.

[Jermolene]

Hi @mklauber the semantics of the equivalent comparison operators can be surprising. For example:

> [] == ""
true // OK
> [""] == ""
true // Problematic
> ["",""] == ""
false // Inconsistent with the above

That's why the core pretty much exclusively uses the exact comparison operators. Here, I think it would be better to explicitly check for an array of length zero, alongside the existing check for an empty string.

[mklauber]

Fixed that. I was possibly a little verbose in how I checked things, but I figured we wanted to be sure we were dealing with an array, before we checked its length.

[Jermolene]

Thanks @mklauber

[Jermolene]

Hi @mklauber I think there's still a problem: the check for tiddler.fields[operator.operand] !== "" will succeed for an empty tags field. I guess we need to guard with a check for the field type being a string.

[mklauber]

@Jermolene, I don't think this is an issue, unless something has recently changed. When I pause the debugger at the time when we hit this line, tiddler.fields.tags = Array[0].

[Jermolene]

In my simple testing I found that #2274 wasn't fixed by this; I only eyeballed the code, and didn't debug it properly.

[mklauber]

Oops, I miss understood what you meant. I understand now.