Strange behavior with locals in arrays

[Yzrsah]

I'm just getting into Jsonnet and I love it. I've wanted something like this for so long! I'm considering using it for everything in a game project.

I'm having some trouble with arrays --

No comma:

OK:

The first use of local works, but the second does not -- is this a bug?

Works with local outside the array:

(Screenshots from use of Jsonnet-LSP)

The language reference says:

Object locals can access self and super – they are “inside the object”. As a consequence of this, object locals are not available in Field Name Expressions, because (in general) they depend on the object being already created, which requires the field names to be already known.

But I'm not sure how this applies to arrays. Please help me to understand what part of it is in the spec, or what part of this might be a bug.

[zarelit]

Hi @Yzrsah, not a developer but I'm a user.

Object locals

As the name says, object locals are for objects only, they behave like a ghost field that you can reference by name in the rest of the object. They cannot be used in arrays.

If you use a comma after local anywhere else not inside an object it will be used to introduce several locals. I can't find examples in the website but it's described in the spec
expr ∈ Expr ::= .... | local bind { , bind } ; expr

So what happens with your examples?

Duplicate local

Original example:

[
    local prefix = "aaa",
    prefix + "bbb"
]

Since this is not an object local, this local expression must end with semicolon. The comma in this context is a shorthand to avoid repeating local, the LSP stops before the plus sign and tells you that prefix has been already declared as a local.

Compare with this example:

[
    local prefix = "aaa",
    something = "bbb";
    something + prefix
]

The outcome is [ "bbbaaaa" ]

Scope of locals

The local applies only to the expression that follows, so this example

[
    local prefix = "aaa";
    prefix + "bbb",
    "ccc",
    prefix + "ddd"
]

does not work because it is interpreted like

[
    (local prefix = "aaa";
    prefix + "bbb"),
    ("ccc"),
    (prefix + "ddd)"
]

The last one works because the local is applied to the whole array (the expression that follows).