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Do you mean not panic when you do type assertion like

intOutput := stringOutput.ApplyT(func(v string) int {
    return len(v)
}).(pulumi.IntOutput)

or something else?

kiiiinda.

intOutput := stringOutput.ApplyT(func(v string) int {
    i, err := foo(v)
    if err != nil {
        // handle this err somehow
    }
    return len(i)
}).(pulumi.IntOutput)

you can just return an error from the internal func:

intOutput := stringOutput.ApplyT(func(v string) (int, error) {
    i, err := foo(v)
    if err != nil {
        // handle this err somehow
    }
    return len(i)
}).(pulumi.IntOutput)

Ah, I think the problem is I was returning an error as the first and only arg. didn’t realize that part of the output interface was error