encoding/xml: fix name spaces

[rsc]

There are many pending issues related to the handling of xml name spaces. We need to rethink this. One more try and then we're going to give up.

• encoding/xml: Encoder duplicates namespace tags #7535 encoding/xml: Encoder duplicates namespace tags
• encoding/xml: Serializing XML with namespace prefix #11496 encoding/xml: Serializing XML with namespace prefix
• encoding/xml: Unmarshal does not properly handle NCName in XML namespaces #9775 encoding/xml: Unmarshal does not properly handle NCName in XML namespaces
• encoding/xml: brittle support for matching a namespace by identifier or url #12624 encoding/xml: brittle support for matching a namespace by identifier or url
• encoding/xml: disallow attributes named xmlns:* #8167 encoding/xml: disallow attributes named xmlns:*
• encoding/xml: empty namespace conventions are badly documented #11735 encoding/xml: empty namespace conventions are badly documented
• encoding/xml: empty namespace prefix definitions should be illegal #8068 encoding/xml: empty namespace prefix definitions should be illegal
• encoding/xml: failure to handle conflicting tags in different namespaces #8535 encoding/xml: failure to handle conflicting tags in different namespaces
• encoding/xml: loss of xmlns= in encoding since Go 1.4 #11431 encoding/xml: loss of xmlns= in encoding since Go 1.4
• encoding/xml: missing nested namespace not handled #7113 encoding/xml: missing nested namespace not handled
• encoding/xml: namespaced and non-namespaced attributes conflict #11724 encoding/xml: namespaced and non-namespaced attributes conflict
• encoding/xml: omit parent tags if value is empty #2 #7233 encoding/xml: omit parent tags if value is empty net: LookupHost is returning odd values and crashing net tests #2
• encoding/xml: support QName values / expose namespace bindings #12406 encoding/xml: support QName values / expose namespace bindings
• encoding/xml: support for XML namespace prefixes #9519 encoding/xml: support for XML namespace prefixes

[aeden]

then we're going to give up

Please don't give up 😄

No doubt that proper namespace handling is a pain, but getting it right is very valuable for those of us who are stuck with legacy APIs that only speak XML.

[justinlindh-wf]

Seconding the comment above. Please don't give up on this. There is still value in handling namespaces properly in golang XML.

[rsc]

I did say we'd try one more time before giving up.

[glenn-de-backer]

+1 I was researching Go as a possible replacement for Python in processing ODT files and I was quickly hitting snags when dealing with multiple namespaces.