Unignore Serializer::serialize_map example

serde/src/ser/mod.rs

@@ -690,12 +690,42 @@ pub trait Serializer: Sized {
     /// be computable before the map is iterated. Some serializers only support
     /// maps whose length is known up front.
     ///
-    /// ```rust,ignore
-    /// let mut map = serializer.serialize_map(Some(self.len()))?;
-    /// for (k, v) in self {
-    ///     map.serialize_entry(k, v)?;
+    /// ```rust
+    /// # use std::marker::PhantomData;
+    /// #
+    /// # struct HashMap<K, V>(PhantomData<K>, PhantomData<V>);
+    /// #
+    /// # impl<K, V> HashMap<K, V> {
+    /// #     fn len(&self) -> usize {
+    /// #         unimplemented!()
+    /// #     }
+    /// # }
+    /// #
+    /// # impl<'a, K, V> IntoIterator for &'a HashMap<K, V> {
+    /// #     type Item = (&'a K, &'a V);
+    /// #     type IntoIter = Box<Iterator<Item = (&'a K, &'a V)>>;
+    /// #     fn into_iter(self) -> Self::IntoIter {
+    /// #         unimplemented!()
+    /// #     }
+    /// # }
+    /// #
+    /// use serde::{Serialize, Serializer};
+    /// use serde::ser::SerializeMap;
+    ///
+    /// impl<K, V> Serialize for HashMap<K, V>
+    ///     where K: Serialize,
+    ///           V: Serialize
+    /// {
+    ///     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    ///         where S: Serializer
+    ///     {
+    ///         let mut map = serializer.serialize_map(Some(self.len()))?;
+    ///         for (k, v) in self {
+    ///             map.serialize_entry(k, v)?;
+    ///         }
+    ///         map.end()
+    ///     }
     /// }
-    /// map.end()
     /// ```
     fn serialize_map(self, len: Option<usize>) -> Result<Self::SerializeMap, Self::Error>;