Duplicate nodes getting added to ancestors array in traverse

[cbranch101]

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When I run the following sample code

    const content = `export const ComponentName = () => {}`;
    // this is just calling ts.createSourceFile
    const ast = parseContents(content, "/test");
    traverse(ast, (node, ancestors) => {
      const ancestorTypes = ancestors.map((a) => SyntaxKind[a.kind]);
      console.log({
        node: SyntaxKind[node.kind],
        ancestors: ancestorTypes,
      });
    });

When processing the VariableDeclaration node, I get the following console log { node: 'VariableDeclaration', ancestors: [ 'VariableDeclarationList', 'VariableDeclarationList', 'FirstStatement', 'SourceFile', 'SourceFile' ] }

The issue seems to be related to the handling of nodes that have SyntaxList children. I think the issue is this code in traverse in particular

  if (node.parent != null) {
    ancestors.unshift(node.parent);
  }

It seems like SyntaxList's parent isn't being assigned correctly, so that step allows the same node to get added twice. This in turn, makes a query like SourceFile > VariableStatement > VariableDeclarationList > VariableDeclaration impossible, where as, for some reason, VariableDeclarationList > VariableDeclaration does work.

I fixed this locally just by adding a duplicate check to traverse, but I am concerned this might introduce issues else where.

  if (node.parent != null && ancestors[0] !== node.parent) {
    ancestors.unshift(node.parent);
  }

[phenomnomnominal]

Has a quick look - would you mind checking if changing:

if (node.parent != null) {
  ancestors.unshift(node.parent);
}
iterator(node, ancestors);
let children: Array<Node> = [];

to:

iterator(node, ancestors);
let children: Array<Node> = [];
ancestors.unshift(node.parent);

Fixes your issue as well? Seems like if there are multiple children for one node, then it can add the item to ancestors multiple times which doesn't really make sense!

[cbranch101]

Ah yep, that also fixes it, good call