B.3.2.1 - Which FunctionDeclaration parse nodes list does it iterate?

[nicolo-ribaudo]

Description:

We are trying to fix the handling of function declarations in blocks in Babel (babel/babel#14203), and I don't understand what the spec does.

At step 29.a of B.3.2.1, it says:

a. For each FunctionDeclaration f that is directly contained in the StatementList of a Block, CaseClause, or DefaultClause, do

However, usually "For each" iterates the elements of a list. Is it iterating over the functions (deeply) contained within the function that is currently being instantiated? Or is it something like "If the current FunctionDeclarationInstantiation call has been caused by evaluating a FunctionDeclaration parse node, let f be that parse node"?

[jmdyck]

I agree that it's odd: the criterion "each FunctionDeclarationthat is directly contained in the StatementList of a Block, CaseClause, or DefaultClause" makes it sound like we need to look at any Block, CaseClause, or DefaultClause, anywhere in the Script.

In ES6, that step is:

For each FunctionDeclaration f in varDeclarations that is directly contained in the StatementList of a Block, CaseClause, or DefaultClause,

(emphasis mine), which makes it clear you don't have to go looking everywhere. But the phrase "in varDeclarations" was removed in efbfc88 to resolve https://tc39.es/archives/bugzilla/4427/, which links back to an issue that @bakkot raised in 2015.

However, it looks like the change that @allenwb suggested in 4427 wasn't applied correctly: in addition to dropping "in varDeclarations", he also appended "Contained within code" (where code is the FunctionBody of the function that FunctionDeclarationInstantiation is being called on), but that wasn't added.

[nicolo-ribaudo]

That might still be somewhat problematic because when instantiating f in

function f() {
  function g() {
    { function h() {} }
  }
}

we don't want to look at h.

[jmdyck]

In the phrase "Contained within code", I suspect the capital 'C' alludes to the 'Contains' SDO, which avoids looking inside nested functionDecls.

(To make it a proper invocation of 'Contains', I think it would need to be something like "... any Block, CaseClause, or DefaultClause x such that code Contains x".)

[bathos]

I read "directly" as specifying that h (indirectly contained) is not considered.

[nicolo-ribaudo]

@bathos In my example the function is directly contained in a block. I'll open a PR with "Contains".

[bathos]

Ah, got it — “directly contained” only describes the declaration relative to the block, not the block relative to the “root” statement list.