feat(spanned): Expose SpannedDeserializer

Fixes toml-rs#634

crates/serde_spanned/src/de.rs

@@ -0,0 +1,81 @@
+//! Deserialzation support for [`Spanned`]
+
+use serde::de::value::BorrowedStrDeserializer;
+use serde::de::IntoDeserializer as _;
+
+use crate::Spanned;
+
+/// Deserializer / format support for emitting [`Spanned`]
+pub struct SpannedDeserializer<'de, T, E>
+where
+    T: serde::de::IntoDeserializer<'de, E>,
+    E: serde::de::Error,
+{
+    start: Option<usize>,
+    end: Option<usize>,
+    value: Option<T>,
+    _lifetime: std::marker::PhantomData<&'de ()>,
+    _error: std::marker::PhantomData<E>,
+}
+
+impl<'de, T, E> SpannedDeserializer<'de, T, E>
+where
+    T: serde::de::IntoDeserializer<'de, E>,
+    E: serde::de::Error,
+{
+    /// Create a deserializer to emit [`Spanned`]
+    pub fn new(value: T, span: std::ops::Range<usize>) -> Self {
+        Self {
+            start: Some(span.start),
+            end: Some(span.end),
+            value: Some(value),
+            _lifetime: Default::default(),
+            _error: Default::default(),
+        }
+    }
+
+    /// Check if deserializing a [`Spanned`]
+    pub fn is_spanned(name: &'static str, fields: &'static [&'static str]) -> bool {
+        Spanned::is_spanned(name, fields)
+    }
+}
+
+impl<'de, T, E> serde::de::MapAccess<'de> for SpannedDeserializer<'de, T, E>
+where
+    T: serde::de::IntoDeserializer<'de, E>,
+    E: serde::de::Error,
+{
+    type Error = E;
+    fn next_key_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>, Self::Error>
+    where
+        K: serde::de::DeserializeSeed<'de>,
+    {
+        if self.start.is_some() {
+            seed.deserialize(BorrowedStrDeserializer::new(Spanned::START_FIELD))
+                .map(Some)
+        } else if self.end.is_some() {
+            seed.deserialize(BorrowedStrDeserializer::new(Spanned::END_FIELD))
+                .map(Some)
+        } else if self.value.is_some() {
+            seed.deserialize(BorrowedStrDeserializer::new(Spanned::VALUE_FIELD))
+                .map(Some)
+        } else {
+            Ok(None)
+        }
+    }
+
+    fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value, Self::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")
+        }
+    }
+}

crates/serde_spanned/src/lib.rs

@@ -16,6 +16,8 @@
 
 mod spanned;
 pub use crate::spanned::Spanned;
+#[cfg(feature = "serde")]
+pub mod de;
 
 #[doc(hidden)]
 #[cfg(feature = "serde")]

crates/serde_spanned/src/spanned.rs

@@ -56,6 +56,17 @@ impl<T> Spanned<T> {
     }
 }
 
+#[cfg(feature = "serde")]
+impl<T> Spanned<T> {
+    pub(crate) const NAME: &str = NAME;
+    pub(crate) const START_FIELD: &str = START_FIELD;
+    pub(crate) const END_FIELD: &str = END_FIELD;
+    pub(crate) const VALUE_FIELD: &str = VALUE_FIELD;
+    pub(crate) fn is_spanned(name: &'static str, fields: &'static [&'static str]) -> bool {
+        is_spanned(name, fields)
+    }
+}
+
 impl std::borrow::Borrow<str> for Spanned<String> {
     fn borrow(&self) -> &str {
         self.get_ref()

crates/toml_edit/src/de/array.rs

@@ -32,9 +32,9 @@ impl<'de> serde::Deserializer<'de> for ArrayDeserializer {
     where
         V: serde::de::Visitor<'de>,
     {
-        if serde_spanned::__unstable::is_spanned(name, fields) {
+        if serde_spanned::SpannedDeserializer::is_spanned(name, fields) {
             if let Some(span) = self.span.clone() {
-                return visitor.visit_map(super::SpannedDeserializer::new(self, span));
+                return visitor.visit_map(serde_spanned::SpannedDeserializer::new(self, span));
             }
         }
 

crates/toml_edit/src/de/key.rs

@@ -54,9 +54,12 @@ impl<'de> serde::de::Deserializer<'de> for KeyDeserializer {
     where
         V: serde::de::Visitor<'de>,
     {
-        if serde_spanned::__unstable::is_spanned(name, fields) {
+        if serde_spanned::SpannedDeserializer::is_spanned(name, fields) {
             if let Some(span) = self.span.clone() {
-                return visitor.visit_map(super::SpannedDeserializer::new(self.key.as_str(), span));
+                return visitor.visit_map(serde_spanned::SpannedDeserializer::new(
+                    self.key.as_str(),
+                    span,
+                ));
             }
         }
         self.deserialize_any(visitor)

crates/toml_edit/src/de/table.rs

@@ -48,9 +48,9 @@ impl<'de> serde::Deserializer<'de> for TableDeserializer {
     where
         V: serde::de::Visitor<'de>,
     {
-        if serde_spanned::__unstable::is_spanned(name, fields) {
+        if serde_spanned::SpannedDeserializer::is_spanned(name, fields) {
             if let Some(span) = self.span.clone() {
-                return visitor.visit_map(super::SpannedDeserializer::new(self, span));
+                return visitor.visit_map(serde_spanned::SpannedDeserializer::new(self, span));
             }
         }
 

crates/toml_edit/src/de/value.rs

@@ -128,9 +128,9 @@ impl<'de> serde::Deserializer<'de> for ValueDeserializer {
     where
         V: serde::de::Visitor<'de>,
     {
-        if serde_spanned::__unstable::is_spanned(name, fields) {
+        if serde_spanned::SpannedDeserializer::is_spanned(name, fields) {
             if let Some(span) = self.input.span() {
-                return visitor.visit_map(super::SpannedDeserializer::new(self, span));
+                return visitor.visit_map(serde_spanned::SpannedDeserializer::new(self, span));
             }
         }