`indexInParent` replacement for use with `replacing(childAt`

[keith]

Description

I had some SwiftSyntax code that did:

override func visit(_ node: ImportDeclSyntax) -> DeclSyntax {
    guard let importAccessPathSyntax = node.path.first(where: { $0.name.text.contains("Foo") }) {
        return super.visit(node)
    }

    let newToken = importAccessPathSyntax.name.withKind(.stringSegment("Bar"))
    let newPath = node.path.replacing(childAt: importAccessPathSyntax.indexInParent,
                                        with: importAccessPathSyntax.with(\.name, newToken))
    let newNode = node.with(\.path, newPath)
    correctionPositions.append(importAccessPathSyntax.positionAfterSkippingLeadingTrivia)
    return super.visit(newNode)
}

In order to replace imports of Foo with Bar. I was able to do this without affecting any trivia using this approach, but it seems like with recent changes on the release/5.9 branch there is no way to get the equivalent of importAccessPathSyntax.indexInParent anymore. I attempted to use importAccessPathSyntax.keyPathInParent as a replacement here but in this case that results in nil. Should that be the new option? Should replacing(childAt: take SyntaxChildrenIndex now instead of an Int? In the meantime I worked around this case by assuming that 0 was the right index always:

override func visit(_ node: ImportDeclSyntax) -> DeclSyntax {
    guard let importAccessPathSyntax = node.path.first(where: { $0.name.text.contains("Foo") }) {
        return super.visit(node)
    }

    let newToken = importAccessPathSyntax.name.with(\.tokenKind, TokenKind.stringSegment("Bar"))
    let newPath = node.path.replacing(childAt: 0, with: importAccessPathSyntax.with(\.name, newToken))
    let newNode = node.with(\.path, newPath)
    correctionPositions.append(importAccessPathSyntax.positionAfterSkippingLeadingTrivia)
    return super.visit(newNode)
}

[ahoppen]

Tracked in Apple’s issue tracker as rdar://111591397

[ahoppen]

You should be able to get the index of the element you want to replace when finding the element that contains “Foo”. This is similar to what you would do in a normal Swift array as well.

override func visit(_ node: ImportDeclSyntax) -> DeclSyntax {
    guard let (index, importAccessPathSyntax) = node.path.enumerated().first(where: { $0.element.name.text.contains("Foo") }) else {
      return super.visit(node)
    }

    let newToken = importAccessPathSyntax.name.with(\.tokenKind, .stringSegment("Bar"))
    let newPath = node.path.replacing(childAt: index, with: importAccessPathSyntax.with(\.name, newToken))
    let newNode = node.with(\.path, newPath)
    correctionPositions.append(importAccessPathSyntax.positionAfterSkippingLeadingTrivia)
    return super.visit(newNode)
}

Thinking about this a little bit more, though, replacing(childAt:with:) probably shouldn’t exist. Instead we should make the subscript on SyntaxCollection writable. I’ll update once I have thought about this a little bit more.

[Matejkob]

I'm wondering if the issue was completely resolved in #1880?

[ahoppen]

I still have two small small items on my to-do list to resolve this. I think I should get to them this week. So: no, not quite resolved yet.

[ahoppen]

Closing this now that we have #1919. I also wanted to do #1921 as part of this but it has SILGen issues on Windows that I need to investigate and it’s not really necessary to resolve this issue.