nth(n) ignores current axis id

[leumasme]

astq/src/astq-funcs-std.js

Lines 75 to 86 in ea8d5c8

	"nth": (A, T, num) => {
	num = parseInt(num, 10)
	let parent = A.getParentNode(T, "*")
	if (parent !== null) {
	let pchilds = A.getChildNodes(parent, "*")
	if (num < 0)
	num = pchilds.length - (num + 1)
	for (let i = 0; i < pchilds.length; i++)
	if (pchilds[i] === T)
	return ((i + 1) === num)
	return false
	}

It seems like nth is implemented by getting the parent, then getting the children on * axis, and finding the element in question.
This produces arguably unexpected cases where nth is called from within a filter on an axis with an id, e.g. I would expect

/ ExpressionStatement / CallExpression /:arguments * [
  nth(1)
]

running on the input ast of

a(1)

to find the 1st argument of the CallExpression (1-based indexing, ouch).
Instead, this query returns nothing, because the 1st child of the CallExpression on axis * is actually the function that was called, located on .callee.
What now? Always just +1 the parameter for nth in this case? Not pretty, and doesn't work on ast nodes with multiple variable-length child arrays.

---

While testing this, I've also found that

/ ExpressionStatement / CallExpression / *

finds 'Identifier', 'Literal', 'ExpressionStatement':
What is happening here? Why is ExpressionStatement, which is the parent of the CallExpression, being matched by this Query?
The readme defines the / Axis as:

• / for direct child nodes

Edit: Turns out this last part is likely caused by astq considering the parent property (which I populated on my mozast to get nth to work) as a valid child axis.

[leumasme]

Considering that

• none of the inbuilt adapters support named parent axis
  • such a thing would generally not make sense in a tree AST
• most of the inbuilt adapters do not support getParentNode at all

it may be a good idea to fully move away from this function. Keeping a parent stack to the current position in the Tree at all times would make the function fully obsolete, and remove any need for a parent property on nodes.
Unfortunately it seems like this library is not updated anymore, aside from basic dependency updates.