Error details leaking

[whitlockjc]

Whenever I try to compile or use an invalid XPath, while an error is returned as expected, two things happen that shouldn't be:

1. The error is missing the inner context
2. The inner context is written to stdout/stderr (not sure which) without any control

Here is the important part of my code:

    doc, err := libxml2.Parse(docBytes)
    if err != nil {
        return err
    }

    expr, err := xpath.NewExpression(xPath)
    if err != nil {
        return err // Never contains the reason for the compilation failure
    }
    defer expr.Free()

    root, err := doc.DocumentElement()
    if err != nil {
        return err
    }

    ctx, err := xpath.NewContext(root)
    if err != nil {
        return err
    }

    res, err := ctx.FindExpr(expr)
    if err != nil {
        return err
    }
    defer res.Free()

    nodes := res.NodeIter()

    for nodes.Next() {
        node := nodes.Node()

        fmt.Printf("%s:\n%s\n", xml.XPathFromNode(node), xml.NodeToString(node))
    }

    return nil

The returned error will always/only contain failed to compile expression: xpath compilation failed but the inner error details are not available no matter how much I unwrap. Also, the inner error details always end up being written to stdout/stderr. Here is example output of my cobra CLI app that uses the code above:

myapp command -x '$.character' /tmp/library.xml
XPath error : Expected $ for variable reference
$.character
 ^
Error: failed to compile expression: xpath compilation failed
Usage:
  referee resolve [flags] DOCUMENT_PATH

Flags:
  -x, --xpath string           The XPath to resolve
  -h, --help                   help for resolve

failed to compile expression: xpath compilation failed

As you can see, the error my app returns does not contain the XPath error details and it is printed before my app prints anything related to the command returning an error. If I printed out the error returned by xpath.NewExpression, it literally only contains failed to compile expression: xpath compilation failed while XPath error: Expected $ for variable reference ... is printed to stdout/stderr but not available by the provided error, nor is there any control on whether the detailed cause is printed at all.

go version go version go1.23-20240626-RC01

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