Revert^2 "Import xml-rs 0.8.3"

2fc140166d67619ad4a9ce3013e2604b8b5845aa

Change-Id: I6fdc0f5dc86abd2b5417e43bae3da28070ad8636
diff --git a/src/namespace.rs b/src/namespace.rs
new file mode 100644
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--- /dev/null
+++ b/src/namespace.rs
@@ -0,0 +1,485 @@
+//! Contains namespace manipulation types and functions.
+
+use std::iter::{Map, Rev};
+use std::collections::btree_map::{BTreeMap, Entry};
+use std::collections::btree_map::Iter as Entries;
+use std::collections::HashSet;
+use std::slice::Iter;
+
+/// Designates prefix for namespace definitions.
+///
+/// See [Namespaces in XML][namespace] spec for more information.
+///
+///   [namespace]: http://www.w3.org/TR/xml-names/#ns-decl
+pub const NS_XMLNS_PREFIX: &'static str = "xmlns";
+
+/// Designates the standard URI for `xmlns` prefix.
+///
+/// See [A Namespace Name for xmlns Attributes][1] for more information.
+///
+///   [namespace]: http://www.w3.org/2000/xmlns/
+pub const NS_XMLNS_URI: &'static str    = "http://www.w3.org/2000/xmlns/";
+
+/// Designates prefix for a namespace containing several special predefined attributes.
+///
+/// See [2.10 White Space handling][1],  [2.1 Language Identification][2],
+/// [XML Base specification][3] and [xml:id specification][4] for more information.
+///
+///   [1]: http://www.w3.org/TR/REC-xml/#sec-white-space
+///   [2]: http://www.w3.org/TR/REC-xml/#sec-lang-tag
+///   [3]: http://www.w3.org/TR/xmlbase/
+///   [4]: http://www.w3.org/TR/xml-id/
+pub const NS_XML_PREFIX: &'static str   = "xml";
+
+/// Designates the standard URI for `xml` prefix.
+///
+/// See `NS_XML_PREFIX` documentation for more information.
+pub const NS_XML_URI: &'static str      = "http://www.w3.org/XML/1998/namespace";
+
+/// Designates the absence of prefix in a qualified name.
+///
+/// This constant should be used to define or query default namespace which should be used
+/// for element or attribute names without prefix. For example, if a namespace mapping
+/// at a particular point in the document contains correspondence like
+///
+/// ```none
+///   NS_NO_PREFIX  -->  urn:some:namespace
+/// ```
+///
+/// then all names declared without an explicit prefix `urn:some:namespace` is assumed as
+/// a namespace URI.
+///
+/// By default empty prefix corresponds to absence of namespace, but this can change either
+/// when writing an XML document (manually) or when reading an XML document (based on namespace
+/// declarations).
+pub const NS_NO_PREFIX: &'static str    = "";
+
+/// Designates an empty namespace URI, which is equivalent to absence of namespace.
+///
+/// This constant should not usually be used directly; it is used to designate that
+/// empty prefix corresponds to absent namespace in `NamespaceStack` instances created with
+/// `NamespaceStack::default()`. Therefore, it can be used to restore `NS_NO_PREFIX` mapping
+/// in a namespace back to its default value.
+pub const NS_EMPTY_URI: &'static str    = "";
+
+/// Namespace is a map from prefixes to namespace URIs.
+///
+/// No prefix (i.e. default namespace) is designated by `NS_NO_PREFIX` constant.
+#[derive(PartialEq, Eq, Clone, Debug)]
+pub struct Namespace(pub BTreeMap<String, String>);
+
+impl Namespace {
+    /// Returns an empty namespace.
+    #[inline]
+    pub fn empty() -> Namespace { Namespace(BTreeMap::new()) }
+
+    /// Checks whether this namespace is empty.
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
+
+    /// Checks whether this namespace is essentially empty, that is, it does not contain
+    /// anything but default mappings.
+    pub fn is_essentially_empty(&self) -> bool {
+        // a shortcut for a namespace which is definitely not empty
+        if self.0.len() > 3 { return false; }
+
+        self.0.iter().all(|(k, v)| match (&**k, &**v) {
+            (NS_NO_PREFIX,    NS_EMPTY_URI) => true,
+            (NS_XMLNS_PREFIX, NS_XMLNS_URI) => true,
+            (NS_XML_PREFIX,   NS_XML_URI)   => true,
+            _ => false
+        })
+    }
+
+    /// Checks whether this namespace mapping contains the given prefix.
+    ///
+    /// # Parameters
+    /// * `prefix`  --- namespace prefix.
+    ///
+    /// # Return value
+    /// `true` if this namespace contains the given prefix, `false` otherwise.
+    #[inline]
+    pub fn contains<P: ?Sized+AsRef<str>>(&self, prefix: &P) -> bool {
+        self.0.contains_key(prefix.as_ref())
+    }
+
+    /// Puts a mapping into this namespace.
+    ///
+    /// This method does not override any already existing mappings.
+    ///
+    /// Returns a boolean flag indicating whether the map already contained
+    /// the given prefix.
+    ///
+    /// # Parameters
+    /// * `prefix` --- namespace prefix;
+    /// * `uri`    --- namespace URI.
+    ///
+    /// # Return value
+    /// `true` if `prefix` has been inserted successfully; `false` if the `prefix`
+    /// was already present in the namespace.
+    pub fn put<P, U>(&mut self, prefix: P, uri: U) -> bool
+        where P: Into<String>, U: Into<String>
+    {
+        match self.0.entry(prefix.into()) {
+            Entry::Occupied(_) => false,
+            Entry::Vacant(ve) => {
+                ve.insert(uri.into());
+                true
+            }
+        }
+    }
+
+    /// Puts a mapping into this namespace forcefully.
+    ///
+    /// This method, unlike `put()`, does replace an already existing mapping.
+    ///
+    /// Returns previous URI which was assigned to the given prefix, if it is present.
+    ///
+    /// # Parameters
+    /// * `prefix` --- namespace prefix;
+    /// * `uri`    --- namespace URI.
+    ///
+    /// # Return value
+    /// `Some(uri)` with `uri` being a previous URI assigned to the `prefix`, or
+    /// `None` if such prefix was not present in the namespace before.
+    pub fn force_put<P, U>(&mut self, prefix: P, uri: U) -> Option<String>
+        where P: Into<String>, U: Into<String>
+    {
+        self.0.insert(prefix.into(), uri.into())
+    }
+
+    /// Queries the namespace for the given prefix.
+    ///
+    /// # Parameters
+    /// * `prefix` --- namespace prefix.
+    ///
+    /// # Return value
+    /// Namespace URI corresponding to the given prefix, if it is present.
+    pub fn get<'a, P: ?Sized+AsRef<str>>(&'a self, prefix: &P) -> Option<&'a str> {
+        self.0.get(prefix.as_ref()).map(|s| &**s)
+    }
+}
+
+/// An alias for iterator type for namespace mappings contained in a namespace.
+pub type NamespaceMappings<'a> = Map<
+    Entries<'a, String, String>,
+    for<'b> fn((&'b String, &'b String)) -> UriMapping<'b>
+>;
+
+impl<'a> IntoIterator for &'a Namespace {
+    type Item = UriMapping<'a>;
+    type IntoIter = NamespaceMappings<'a>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        fn mapper<'a>((prefix, uri): (&'a String, &'a String)) -> UriMapping<'a> {
+            (&*prefix, &*uri)
+        }
+        self.0.iter().map(mapper)
+    }
+}
+
+/// Namespace stack is a sequence of namespaces.
+///
+/// Namespace stack is used to represent cumulative namespace consisting of
+/// combined namespaces from nested elements.
+#[derive(Clone, Eq, PartialEq, Debug)]
+pub struct NamespaceStack(pub Vec<Namespace>);
+
+impl NamespaceStack {
+    /// Returns an empty namespace stack.
+    #[inline]
+    pub fn empty() -> NamespaceStack { NamespaceStack(Vec::with_capacity(2)) }
+
+    /// Returns a namespace stack with default items in it.
+    ///
+    /// Default items are the following:
+    ///
+    /// * `xml` → `http://www.w3.org/XML/1998/namespace`;
+    /// * `xmlns` → `http://www.w3.org/2000/xmlns/`.
+    #[inline]
+    pub fn default() -> NamespaceStack {
+        let mut nst = NamespaceStack::empty();
+        nst.push_empty();
+        // xml namespace
+        nst.put(NS_XML_PREFIX, NS_XML_URI);
+        // xmlns namespace
+        nst.put(NS_XMLNS_PREFIX, NS_XMLNS_URI);
+        // empty namespace
+        nst.put(NS_NO_PREFIX, NS_EMPTY_URI);
+        nst
+    }
+
+    /// Adds an empty namespace to the top of this stack.
+    #[inline]
+    pub fn push_empty(&mut self) -> &mut NamespaceStack {
+        self.0.push(Namespace::empty());
+        self
+    }
+
+    /// Removes the topmost namespace in this stack.
+    ///
+    /// Panics if the stack is empty.
+    #[inline]
+    pub fn pop(&mut self) -> Namespace {
+        self.0.pop().unwrap()
+    }
+
+    /// Removes the topmost namespace in this stack.
+    ///
+    /// Returns `Some(namespace)` if this stack is not empty and `None` otherwise.
+    #[inline]
+    pub fn try_pop(&mut self) -> Option<Namespace> {
+        self.0.pop()
+    }
+
+    /// Borrows the topmost namespace mutably, leaving the stack intact.
+    ///
+    /// Panics if the stack is empty.
+    #[inline]
+    pub fn peek_mut(&mut self) -> &mut Namespace {
+        self.0.last_mut().unwrap()
+    }
+
+    /// Borrows the topmost namespace immutably, leaving the stack intact.
+    ///
+    /// Panics if the stack is empty.
+    #[inline]
+    pub fn peek(&self) -> &Namespace {
+        self.0.last().unwrap()
+    }
+
+    /// Puts a mapping into the topmost namespace if this stack does not already contain one.
+    ///
+    /// Returns a boolean flag indicating whether the insertion has completed successfully.
+    /// Note that both key and value are matched and the mapping is inserted if either
+    /// namespace prefix is not already mapped, or if it is mapped, but to a different URI.
+    ///
+    /// # Parameters
+    /// * `prefix` --- namespace prefix;
+    /// * `uri`    --- namespace URI.
+    ///
+    /// # Return value
+    /// `true` if `prefix` has been inserted successfully; `false` if the `prefix`
+    /// was already present in the namespace stack.
+    pub fn put_checked<P, U>(&mut self, prefix: P, uri: U) -> bool
+        where P: Into<String> + AsRef<str>,
+              U: Into<String> + AsRef<str>
+    {
+        if self.0.iter().any(|ns| ns.get(&prefix) == Some(uri.as_ref())) {
+            false
+        } else {
+            self.put(prefix, uri);
+            true
+        }
+    }
+
+    /// Puts a mapping into the topmost namespace in this stack.
+    ///
+    /// This method does not override a mapping in the topmost namespace if it is
+    /// already present, however, it does not depend on other namespaces in the stack,
+    /// so it is possible to put a mapping which is present in lower namespaces.
+    ///
+    /// Returns a boolean flag indicating whether the insertion has completed successfully.
+    ///
+    /// # Parameters
+    /// * `prefix` --- namespace prefix;
+    /// * `uri`    --- namespace URI.
+    ///
+    /// # Return value
+    /// `true` if `prefix` has been inserted successfully; `false` if the `prefix`
+    /// was already present in the namespace.
+    #[inline]
+    pub fn put<P, U>(&mut self, prefix: P, uri: U) -> bool
+        where P: Into<String>, U: Into<String>
+    {
+        self.0.last_mut().unwrap().put(prefix, uri)
+    }
+
+    /// Performs a search for the given prefix in the whole stack.
+    ///
+    /// This method walks the stack from top to bottom, querying each namespace
+    /// in order for the given prefix. If none of the namespaces contains the prefix,
+    /// `None` is returned.
+    ///
+    /// # Parameters
+    /// * `prefix` --- namespace prefix.
+    #[inline]
+    pub fn get<'a, P: ?Sized+AsRef<str>>(&'a self, prefix: &P) -> Option<&'a str> {
+        let prefix = prefix.as_ref();
+        for ns in self.0.iter().rev() {
+            match ns.get(prefix) {
+                None => {},
+                r => return r,
+            }
+        }
+        None
+    }
+
+    /// Combines this stack of namespaces into a single namespace.
+    ///
+    /// Namespaces are combined in left-to-right order, that is, rightmost namespace
+    /// elements take priority over leftmost ones.
+    pub fn squash(&self) -> Namespace {
+        let mut result = BTreeMap::new();
+        for ns in self.0.iter() {
+            result.extend(ns.0.iter().map(|(k, v)| (k.clone(), v.clone())));
+        }
+        Namespace(result)
+    }
+
+    /// Returns an object which implements `Extend` using `put_checked()` instead of `put()`.
+    ///
+    /// See `CheckedTarget` for more information.
+    #[inline]
+    pub fn checked_target(&mut self) -> CheckedTarget {
+        CheckedTarget(self)
+    }
+
+    /// Returns an iterator over all mappings in this namespace stack.
+    #[inline]
+    pub fn iter(&self) -> NamespaceStackMappings {
+        self.into_iter()
+    }
+}
+
+/// An iterator over mappings from prefixes to URIs in a namespace stack.
+///
+/// # Example
+/// ```
+/// # use xml::namespace::NamespaceStack;
+/// let mut nst = NamespaceStack::empty();
+/// nst.push_empty();
+/// nst.put("a", "urn:A");
+/// nst.put("b", "urn:B");
+/// nst.push_empty();
+/// nst.put("c", "urn:C");
+///
+/// assert_eq!(vec![("c", "urn:C"), ("a", "urn:A"), ("b", "urn:B")], nst.iter().collect::<Vec<_>>());
+/// ```
+pub struct NamespaceStackMappings<'a> {
+    namespaces: Rev<Iter<'a, Namespace>>,
+    current_namespace: Option<NamespaceMappings<'a>>,
+    used_keys: HashSet<&'a str>
+}
+
+impl<'a> NamespaceStackMappings<'a> {
+    fn go_to_next_namespace(&mut self) -> bool {
+        self.current_namespace = self.namespaces.next().map(|ns| ns.into_iter());
+        self.current_namespace.is_some()
+    }
+}
+
+impl<'a> Iterator for NamespaceStackMappings<'a> {
+    type Item = UriMapping<'a>;
+
+    fn next(&mut self) -> Option<UriMapping<'a>> {
+        // If there is no current namespace and no next namespace, we're finished
+        if self.current_namespace.is_none() && !self.go_to_next_namespace() {
+            return None;
+        }
+        let next_item = self.current_namespace.as_mut().unwrap().next();
+
+        match next_item {
+            // There is an element in the current namespace
+            Some((k, v)) => if self.used_keys.contains(&k) {
+                // If the current key is used, go to the next one
+                self.next()
+            } else {
+                // Otherwise insert the current key to the set of used keys and
+                // return the mapping
+                self.used_keys.insert(k);
+                Some((k, v))
+            },
+            // Current namespace is exhausted
+            None => if self.go_to_next_namespace() {
+                // If there is next namespace, continue from it
+                self.next()
+            } else {
+                // No next namespace, exiting
+                None
+            }
+        }
+    }
+}
+
+impl<'a> IntoIterator for &'a NamespaceStack {
+    type Item = UriMapping<'a>;
+    type IntoIter = NamespaceStackMappings<'a>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        NamespaceStackMappings {
+            namespaces: self.0.iter().rev(),
+            current_namespace: None,
+            used_keys: HashSet::new()
+        }
+    }
+}
+
+/// A type alias for a pair of `(prefix, uri)` values returned by namespace iterators.
+pub type UriMapping<'a> = (&'a str, &'a str);
+
+impl<'a> Extend<UriMapping<'a>> for Namespace {
+    fn extend<T>(&mut self, iterable: T) where T: IntoIterator<Item=UriMapping<'a>> {
+        for (prefix, uri) in iterable {
+            self.put(prefix, uri);
+        }
+    }
+}
+
+impl<'a> Extend<UriMapping<'a>> for NamespaceStack {
+    fn extend<T>(&mut self, iterable: T) where T: IntoIterator<Item=UriMapping<'a>> {
+        for (prefix, uri) in iterable {
+            self.put(prefix, uri);
+        }
+    }
+}
+
+/// A wrapper around `NamespaceStack` which implements `Extend` using `put_checked()`.
+///
+/// # Example
+///
+/// ```
+/// # use xml::namespace::NamespaceStack;
+///
+/// let mut nst = NamespaceStack::empty();
+/// nst.push_empty();
+/// nst.put("a", "urn:A");
+/// nst.put("b", "urn:B");
+/// nst.push_empty();
+/// nst.put("c", "urn:C");
+///
+/// nst.checked_target().extend(vec![("a", "urn:Z"), ("b", "urn:B"), ("c", "urn:Y"), ("d", "urn:D")]);
+/// assert_eq!(
+///     vec![("a", "urn:Z"), ("c", "urn:C"), ("d", "urn:D"), ("b", "urn:B")],
+///     nst.iter().collect::<Vec<_>>()
+/// );
+/// ```
+///
+/// Compare:
+///
+/// ```
+/// # use xml::namespace::NamespaceStack;
+/// # let mut nst = NamespaceStack::empty();
+/// # nst.push_empty();
+/// # nst.put("a", "urn:A");
+/// # nst.put("b", "urn:B");
+/// # nst.push_empty();
+/// # nst.put("c", "urn:C");
+///
+/// nst.extend(vec![("a", "urn:Z"), ("b", "urn:B"), ("c", "urn:Y"), ("d", "urn:D")]);
+/// assert_eq!(
+///     vec![("a", "urn:Z"), ("b", "urn:B"), ("c", "urn:C"), ("d", "urn:D")],
+///     nst.iter().collect::<Vec<_>>()
+/// );
+/// ```
+pub struct CheckedTarget<'a>(&'a mut NamespaceStack);
+
+impl<'a, 'b> Extend<UriMapping<'b>> for CheckedTarget<'a> {
+    fn extend<T>(&mut self, iterable: T) where T: IntoIterator<Item=UriMapping<'b>> {
+        for (prefix, uri) in iterable {
+            self.0.put_checked(prefix, uri);
+        }
+    }
+}