Add seeded versions of deserialize functions.

src/de.rs

@@ -997,20 +997,9 @@ impl<'de, 'a, 'r> de::Deserializer<'de> for &'r mut Deserializer<'a> {
     }
 }
 
-/// Deserialize an instance of type `T` from a string of YAML text.
-///
-/// This conversion can fail if the structure of the Value does not match the
-/// structure expected by `T`, for example if `T` is a struct type but the Value
-/// contains something other than a YAML map. It can also fail if the structure
-/// is correct but `T`'s implementation of `Deserialize` decides that something
-/// is wrong with the data, for example required struct fields are missing from
-/// the YAML map or some number is too big to fit in the expected primitive
-/// type.
-///
-/// YAML currently does not support zero-copy deserialization.
-pub fn from_str<T>(s: &str) -> Result<T>
+fn from_str_with<F, U>(s: &str, op: F) -> Result<U>
 where
-    T: DeserializeOwned,
+    F: FnOnce(&mut Deserializer) -> Result<U>,
 {
     let mut parser = Parser::new(s.chars());
     let mut loader = Loader {
@@ -1024,7 +1013,7 @@ where
         Err(private::error_end_of_stream())
     } else {
         let mut pos = 0;
-        let t = Deserialize::deserialize(&mut Deserializer {
+        let t = op(&mut Deserializer {
             events: &loader.events,
             aliases: &loader.aliases,
             pos: &mut pos,
@@ -1039,6 +1028,64 @@ where
     }
 }
 
+fn from_reader_with<R, F, U>(mut rdr: R, op: F) -> Result<U>
+where
+    R: io::Read,
+    F: FnOnce(&str) -> Result<U>,
+{
+    let mut bytes = Vec::new();
+    rdr.read_to_end(&mut bytes).map_err(private::error_io)?;
+    let s = str::from_utf8(&bytes).map_err(private::error_str_utf8)?;
+    op(s)
+}
+
+fn from_slice_with<F, U>(v: &[u8], op: F) -> Result<U>
+where
+    F: FnOnce(&str) -> Result<U>,
+{
+    let s = str::from_utf8(v).map_err(private::error_str_utf8)?;
+    op(s)
+}
+
+/// Deserialize an instance of type `T` from a string of YAML text.
+///
+/// This conversion can fail if the structure of the Value does not match the
+/// structure expected by `T`, for example if `T` is a struct type but the Value
+/// contains something other than a YAML map. It can also fail if the structure
+/// is correct but `T`'s implementation of `Deserialize` decides that something
+/// is wrong with the data, for example required struct fields are missing from
+/// the YAML map or some number is too big to fit in the expected primitive
+/// type.
+///
+/// YAML currently does not support zero-copy deserialization.
+pub fn from_str<T>(s: &str) -> Result<T>
+where
+    T: DeserializeOwned,
+{
+    // This closure is required because Rust can't currently seem to understand
+    // that a for<T: Trait> fn(T) is also a FnOnce(Type) where Type: Trait.
+    #[allow(redundant_closure)]
+    from_str_with(s, |de| Deserialize::deserialize(de))
+}
+
+/// Deserialize an instance of type `T` from a string of YAML text with a seed.
+///
+/// This conversion can fail if the structure of the Value does not match the
+/// structure expected by `T`, for example if `T` is a struct type but the Value
+/// contains something other than a YAML map. It can also fail if the structure
+/// is correct but `T`'s implementation of `Deserialize` decides that something
+/// is wrong with the data, for example required struct fields are missing from
+/// the YAML map or some number is too big to fit in the expected primitive
+/// type.
+///
+/// YAML currently does not support zero-copy deserialization.
+pub fn from_str_seed<T, S>(s: &str, seed: S) -> Result<T>
+where
+    S: for<'de> DeserializeSeed<'de, Value = T>,
+{
+    from_str_with(s, |de| seed.deserialize(de))
+}
+
 /// Deserialize an instance of type `T` from an IO stream of YAML.
 ///
 /// This conversion can fail if the structure of the Value does not match the
@@ -1048,15 +1095,29 @@ where
 /// is wrong with the data, for example required struct fields are missing from
 /// the YAML map or some number is too big to fit in the expected primitive
 /// type.
-pub fn from_reader<R, T>(mut rdr: R) -> Result<T>
+pub fn from_reader<R, T>(rdr: R) -> Result<T>
 where
     R: io::Read,
     T: DeserializeOwned,
 {
-    let mut bytes = Vec::new();
-    rdr.read_to_end(&mut bytes).map_err(private::error_io)?;
-    let s = str::from_utf8(&bytes).map_err(private::error_str_utf8)?;
-    from_str(s)
+    from_reader_with(rdr, from_str)
+}
+
+/// Deserialize an instance of type `T` from an IO stream of YAML with a seed.
+///
+/// This conversion can fail if the structure of the Value does not match the
+/// structure expected by `T`, for example if `T` is a struct type but the Value
+/// contains something other than a YAML map. It can also fail if the structure
+/// is correct but `T`'s implementation of `Deserialize` decides that something
+/// is wrong with the data, for example required struct fields are missing from
+/// the YAML map or some number is too big to fit in the expected primitive
+/// type.
+pub fn from_reader_seed<R, T, S>(rdr: R, seed: S) -> Result<T>
+where
+    R: io::Read,
+    S: for<'de> DeserializeSeed<'de, Value = T>,
+{
+    from_reader_with(rdr, |s| from_str_seed(s, seed))
 }
 
 /// Deserialize an instance of type `T` from bytes of YAML text.
@@ -1074,6 +1135,23 @@ pub fn from_slice<T>(v: &[u8]) -> Result<T>
 where
     T: DeserializeOwned,
 {
-    let s = str::from_utf8(v).map_err(private::error_str_utf8)?;
-    from_str(s)
+    from_slice_with(v, from_str)
+}
+
+/// Deserialize an instance of type `T` from bytes of YAML text with a seed.
+///
+/// This conversion can fail if the structure of the Value does not match the
+/// structure expected by `T`, for example if `T` is a struct type but the Value
+/// contains something other than a YAML map. It can also fail if the structure
+/// is correct but `T`'s implementation of `Deserialize` decides that something
+/// is wrong with the data, for example required struct fields are missing from
+/// the YAML map or some number is too big to fit in the expected primitive
+/// type.
+///
+/// YAML currently does not support zero-copy deserialization.
+pub fn from_slice_seed<T, S>(v: &[u8], seed: S) -> Result<T>
+where
+    S: for<'de> DeserializeSeed<'de, Value = T>,
+{
+    from_slice_with(v, |s| from_str_seed(s, seed))
 }

src/lib.rs

@@ -99,6 +99,11 @@ pub use self::mapping::Mapping;
 pub use self::ser::{to_string, to_vec, to_writer};
 pub use self::value::{from_value, to_value, Index, Number, Sequence, Value};
 
+/// Deserialization with seeds
+pub mod seed {
+    pub use super::de::{from_reader_seed, from_slice_seed, from_str_seed};
+}
+
 mod de;
 mod error;
 mod mapping;

tests/test_de.rs

@@ -25,6 +25,18 @@ where
     serde_yaml::from_str::<serde::de::IgnoredAny>(yaml).unwrap();
 }
 
+fn test_de_seed<T, S>(yaml: &str, seed: S, expected: &T)
+where
+    T: PartialEq + Debug,
+    S: for<'de> serde::de::DeserializeSeed<'de, Value = T>,
+{
+    let deserialized: T = serde_yaml::seed::from_str_seed(yaml, seed).unwrap();
+    assert_eq!(*expected, deserialized);
+
+    serde_yaml::from_str::<serde_yaml::Value>(yaml).unwrap();
+    serde_yaml::from_str::<serde::de::IgnoredAny>(yaml).unwrap();
+}
+
 #[test]
 fn test_alias() {
     let yaml = unindent(
@@ -352,3 +364,40 @@ fn test_numbers() {
         }
     }
 }
+
+#[test]
+fn test_stateful() {
+    struct Seed(i64);
+
+    impl<'de> serde::de::DeserializeSeed<'de> for Seed {
+        type Value = i64;
+        fn deserialize<D>(self, deserializer: D) -> Result<i64, D::Error>
+        where
+            D: serde::de::Deserializer<'de>,
+        {
+            struct Visitor(i64);
+            impl<'de> serde::de::Visitor<'de> for Visitor {
+                type Value = i64;
+
+                fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
+                    write!(formatter, "an integer")
+                }
+
+                fn visit_i64<E: serde::de::Error>(self, v: i64) -> Result<i64, E> {
+                    Ok(v * self.0)
+                }
+
+                fn visit_u64<E: serde::de::Error>(self, v: u64) -> Result<i64, E> {
+                    Ok(v as i64 * self.0)
+                }
+            }
+
+            deserializer.deserialize_any(Visitor(self.0))
+        }
+    }
+
+    let cases = [("3", 5, 15), ("6", 7, 42), ("-5", 9, -45)];
+    for &(yaml, seed, expected) in &cases {
+        test_de_seed(yaml, Seed(seed), &expected);
+    }
+}