Problem and Proposal

Currently, an arbitrary Go value marshalled to XML with a (non-local) XML namespace sets the default namespace for its start element and all elements contained within it. For example, a value with local name "foo" in the "bar" namespace would be marshalled as

<foo xmlns="bar"/>

While this leads to succinct XML most of the times, it does not work well with the newly added 1.5 feature to declare custom namespace prefixes: the xml.Encoder marshals the xml prefix declarations but ignores them while marshalling inner XML elements (see the example below).

I propose to make the declaration of default namespaces optional, and activated by default for backward-compatibility. To do so, I outlined a proof of concept in CL 11074.

Example

A value of type

type Foo struct {
    XMLName xml.Name `xml:"foons foo"`
    Bar     string   `xml:"barns bar"`
}

encoded with EncodeElement and explicitly declared namespace prefixes "f" for "foons" and "b" for "barns" is currently marshalled as

<foo xmlns="foons" xmlns:b="barns" xmlns:f="foons">
   <bar xmlns="barns"></bar>
</foo>

whereas the following output might be expected

<f:foo xmlns:b="barns" xmlns:f="foons">
  <b:bar></b:bar>
</f:foo>