stevedlawrence commented on a change in pull request #505:
URL: https://github.com/apache/daffodil/pull/505#discussion_r624122775
##########
File path:
daffodil-runtime1/src/main/scala/org/apache/daffodil/infoset/SAXInfosetOutputter.scala
##########
@@ -145,18 +145,11 @@ class SAXInfosetOutputter(xmlReader:
DFDL.DaffodilParseXMLReader,
private def doStartPrefixMapping(diElem: DIElement, contentHandler:
ContentHandler): Unit = {
val (nsbStart: NamespaceBinding, nsbEnd: NamespaceBinding) =
getNsbStartAndEnd(diElem)
var n = nsbStart
- var mappingsList: Seq[(String, String)] = Seq()
while (n.ne(nsbEnd) && n.ne(null) && n.ne(scala.xml.TopScope)) {
val prefix = if (n.prefix == null) "" else n.prefix
val uri = if (n.uri == null) "" else n.uri
- // we generate a list here by prepending so can build the prefixMapping
in the
- // same order as it is in minimizedScope when we call
startPrefixMapping; we do this because
- // getPrefix in the contentHandler is order dependent
- mappingsList +:= (prefix, uri)
- n = n.parent
- }
- mappingsList.foreach{ case (prefix, uri) =>
contentHandler.startPrefixMapping(prefix, uri)
+ n = n.parent
Review comment:
Yep, your mental parse is correct.
> But to any other content handler what was a(b(c)) in the minimized scope
would now have become c(b(a)), no?
I think the answer to this is in most cases it doesn't matter, and if it
does it's up to the ContentHandler to decide. Here's my thought process:
If the minimizedScope was a(b(c)), to Daffodil that reprents bindings in
this order when converted to text:
```xml
<a xmlns:a="1" xmlns:b="2" xmlns:c="3" />
```
And so we will call startPrefixMapping in the order of a, b, c. This matces
the order that the xmlns appears in the text representation. And I think that's
all that matters. How a ContentHandler interprets these mapping and uses them
for prefix lookups or converting to text is entirely up to them. Keep in mind
they don't have to use NamespaceBindings. Maybe they use a stack of Maps or
some complicated data structure. All we are really saying by calling
startPrefixMapping is "this is the order we think the xmlns mappings appear in
the text representation, you figure out the rest".
And in most cases, order probably doesn't even matter. If they end up
creating a NamespaceBinding that is c(b(a)) and do prefix lookups on that, the
results will be exactly the same. This is because order doesn't matter in
namespace bindings in relation to a single element (*see potential issue at
bottom*). For example this is exactly the same as the above XML from a prefix
lookup perspective:
```xml
<a xmlns:c="3" xmlns:b="2" xmlns:c="1" />
```
Regardless of the order of those mappings, the a, b, and c prefixes all map
to the right uri. A ContentHandler could add those three to a NamespaceBinding
(or any data structure of choosing) in any order and prefix lookups would work
exactly the same (as long as they took precendece to any outer scope prefixes).
The issue that potentially pops up is if a ContentHandler wants to convert
the prefix mappings to XML text, like our DaffodilParseOutputStream thing does.
In that case, we might care about the order of things, because it is no longer
just about mappings (where order doesn't matter), but is now about outputing
XML text (where order does kindof matter because of our tests). So our content
handler is careful to outut xmlns text in the same order it recieves the
mappings using the new NamespaceBinding.
---
I think maybe the only case where order might matter with prefix look ups is
if you had something like this:
```xml
<pre:a xmlns:pre="foo" xmlns:pre="bar" />
```
So you have the same prefix that maps to two diferent URIs. In that case,
there are two potential namespace bindings depending on order:
```scala
NamespaceBinding("pre", "foo", NamespaceBinding("pre, "bar", null))
NamespaceBinding("pre", "bar", NamespaceBinding("pre, "foo", null))
```
So depending on which NamespaceBinding is used, a prefix lookup of "pre"
could return either "foo" or "bar". But it feels to me like redefining a prefix
on the same element shouldn't even be allowed--order isn't supposed to matter
in prefix mappings, so if prefix redefinition on a single element was allowed,
then order would be the only other thing to pick a winner. I would guess this
is illegal and isn't even something Daffodil would ever do.
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