1 files changed, 70 insertions, 0 deletions
diff --git a/src/de/spanned.rs b/src/de/spanned.rs
new file mode 100644
index 0000000..7ce5864
--- /dev/null
+++ b/src/de/spanned.rs
@@ -0,0 +1,70 @@
+use serde::de::value::BorrowedStrDeserializer;
+use serde::de::IntoDeserializer as _;
+
+use super::Error;
+
+pub(crate) struct SpannedDeserializer<'de, T: serde::de::IntoDeserializer<'de, Error>> {
+    phantom_data: std::marker::PhantomData<&'de ()>,
+    start: Option<usize>,
+    end: Option<usize>,
+    value: Option<T>,
+}
+
+impl<'de, T> SpannedDeserializer<'de, T>
+where
+    T: serde::de::IntoDeserializer<'de, Error>,
+{
+    pub(crate) fn new(value: T, span: std::ops::Range<usize>) -> Self {
+        Self {
+            phantom_data: Default::default(),
+            start: Some(span.start),
+            end: Some(span.end),
+            value: Some(value),
+        }
+    }
+}
+
+impl<'de, T> serde::de::MapAccess<'de> for SpannedDeserializer<'de, T>
+where
+    T: serde::de::IntoDeserializer<'de, Error>,
+{
+    type Error = Error;
+    fn next_key_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>, Error>
+    where
+        K: serde::de::DeserializeSeed<'de>,
+    {
+        if self.start.is_some() {
+            seed.deserialize(BorrowedStrDeserializer::new(
+                serde_spanned::__unstable::START_FIELD,
+            ))
+            .map(Some)
+        } else if self.end.is_some() {
+            seed.deserialize(BorrowedStrDeserializer::new(
+                serde_spanned::__unstable::END_FIELD,
+            ))
+            .map(Some)
+        } else if self.value.is_some() {
+            seed.deserialize(BorrowedStrDeserializer::new(
+                serde_spanned::__unstable::VALUE_FIELD,
+            ))
+            .map(Some)
+        } else {
+            Ok(None)
+        }
+    }
+
+    fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value, Error>
+    where
+        V: serde::de::DeserializeSeed<'de>,
+    {
+        if let Some(start) = self.start.take() {
+            seed.deserialize(start.into_deserializer())
+        } else if let Some(end) = self.end.take() {
+            seed.deserialize(end.into_deserializer())
+        } else if let Some(value) = self.value.take() {
+            seed.deserialize(value.into_deserializer())
+        } else {
+            panic!("next_value_seed called before next_key_seed")
+        }
+    }
+}