Are error comparisons supported? about go-cmp HOT 4 CLOSED

// equateNilError reports errors to be equal only if both are nil.
equateNilError := cmp.Comparer(func(x, y error) bool {
    return x == nil && y == nil
})

// equateAnyError reports errors to be equal only if both are nil or both are non-nil.
equateAnyError := cmp.Comparer(func(x, y error) bool {
    return (x == nil) == (y == nil)
})

// equateErrorMessage reports errors to be equal if both are nil
// or both have the same message.
equateErrorMessage := cmp.Comparer(func(x, y error) bool {
    if x == nil || y == nil {
        return x == nil && y == nil
    }
    return x.Error() == y.Error()
})

// sentinelErrors is a set of common sentinel errors
// (i.e., those that are safe to compare directly using the == operator.
sentinelErrors := map[error]bool{io.EOF: true, io.ErrUnexpectedEOF: true, ...}

equateError := cmp.Comparer(func(x, y error) bool {
    if x == nil || y == nil {
        return x == nil && y == nil
    }

    // Check if x and y are sentinel errors.
    if sentinelErrors[x] || sentinelErrors[y] {
        return x == y
    }

    // Compare error based on their properties.
    switch {
    case os.IsExist(x) || os.IsExist(y):
        return os.IsExist(x) && os.IsExist(y)
    case os.IsPathSeparator(x) || os.IsPathSeparator(y):
        return os.IsPathSeparator(x) && os.IsPathSeparator(y)
    case os.IsPermission(x) || os.IsPermission(y):
        return os.IsPermission(x) && os.IsPermission(y)
    }

    // Default to saying that errors are equal
    return true
})

// equalError reports whether errors a and b are considered equal.
// They're equal if both are nil, or both are not nil and a.Error() == b.Error().
func equalError(a, b error) bool {
	return a == nil && b == nil || a != nil && b != nil && a.Error() == b.Error()
}