Add TryIntoStruct trait for ergonomic result parsing into a struct.

trustfall_core/src/lib.rs

@@ -14,8 +14,11 @@ pub mod graphql_query;
 pub mod interpreter;
 pub mod ir;
 pub mod schema;
+mod serialization;
 mod util;
 
+pub use serialization::TryIntoStruct;
+
 #[cfg(test)]
 mod numbers_interpreter;
 

trustfall_core/src/main.rs

@@ -16,6 +16,7 @@ mod ir;
 mod nullables_interpreter;
 mod numbers_interpreter;
 mod schema;
+mod serialization;
 mod util;
 
 use std::{

trustfall_core/src/serialization/deserializers.rs

@@ -0,0 +1,267 @@
+use std::{collections::BTreeMap, sync::Arc};
+
+use serde::de::{self, IntoDeserializer};
+
+use crate::ir::FieldValue;
+
+#[derive(Debug, Clone)]
+pub(super) struct QueryResultDeserializer {
+    query_result: BTreeMap<Arc<str>, FieldValue>,
+}
+
+impl QueryResultDeserializer {
+    pub(super) fn new(query_result: BTreeMap<Arc<str>, FieldValue>) -> Self {
+        Self { query_result }
+    }
+}
+
+#[derive(Debug, Clone)]
+struct QueryResultMapDeserializer<I: Iterator<Item = (Arc<str>, FieldValue)>> {
+    iter: I,
+    next_value: Option<FieldValue>,
+}
+
+impl<I: Iterator<Item = (Arc<str>, FieldValue)>> QueryResultMapDeserializer<I> {
+    fn new(iter: I) -> Self {
+        Self {
+            iter,
+            next_value: Default::default(),
+        }
+    }
+}
+
+#[derive(Debug, Clone, thiserror::Error)]
+pub enum Error {
+    #[error("error from deserialize: {0}")]
+    Custom(String),
+}
+
+impl de::Error for Error {
+    fn custom<T>(msg: T) -> Self
+    where
+        T: std::fmt::Display,
+    {
+        Self::Custom(msg.to_string())
+    }
+}
+
+impl<'de> de::Deserializer<'de> for QueryResultDeserializer {
+    type Error = Error;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_map(QueryResultMapDeserializer::new(
+            self.query_result.into_iter(),
+        ))
+    }
+
+    serde::forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+        bytes byte_buf option unit unit_struct newtype_struct seq tuple
+        tuple_struct map struct enum identifier ignored_any
+    }
+}
+
+impl<'de, I: Iterator<Item = (Arc<str>, FieldValue)>> de::MapAccess<'de>
+    for QueryResultMapDeserializer<I>
+{
+    type Error = Error;
+
+    fn next_key_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>, Self::Error>
+    where
+        K: de::DeserializeSeed<'de>,
+    {
+        self.iter
+            .next()
+            .map(|(key, value)| {
+                self.next_value = Some(value);
+                seed.deserialize(key.into_deserializer())
+            })
+            .transpose()
+    }
+
+    fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::DeserializeSeed<'de>,
+    {
+        seed.deserialize(
+            self.next_value
+                .take()
+                .expect("called next_value_seed out of order")
+                .into_deserializer(),
+        )
+    }
+}
+
+pub struct FieldValueDeserializer {
+    value: FieldValue,
+}
+
+impl<'de> de::IntoDeserializer<'de, Error> for FieldValue {
+    type Deserializer = FieldValueDeserializer;
+
+    fn into_deserializer(self) -> Self::Deserializer {
+        FieldValueDeserializer { value: self }
+    }
+}
+
+impl<'de> de::Deserializer<'de> for FieldValueDeserializer {
+    type Error = Error;
+
+    fn deserialize_i8<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value {
+            FieldValue::Int64(v) => {
+                visitor.visit_i8(v.try_into().map_err(<Self::Error as de::Error>::custom)?)
+            }
+            FieldValue::Uint64(v) => {
+                visitor.visit_i8(v.try_into().map_err(<Self::Error as de::Error>::custom)?)
+            }
+            _ => self.deserialize_any(visitor), // we'll let `deserialize_any()` raise the error
+        }
+    }
+
+    fn deserialize_i16<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value {
+            FieldValue::Int64(v) => {
+                visitor.visit_i16(v.try_into().map_err(<Self::Error as de::Error>::custom)?)
+            }
+            FieldValue::Uint64(v) => {
+                visitor.visit_i16(v.try_into().map_err(<Self::Error as de::Error>::custom)?)
+            }
+            _ => self.deserialize_any(visitor), // we'll let `deserialize_any()` raise the error
+        }
+    }
+
+    fn deserialize_i32<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value {
+            FieldValue::Int64(v) => {
+                visitor.visit_i32(v.try_into().map_err(<Self::Error as de::Error>::custom)?)
+            }
+            FieldValue::Uint64(v) => {
+                visitor.visit_i32(v.try_into().map_err(<Self::Error as de::Error>::custom)?)
+            }
+            _ => self.deserialize_any(visitor), // we'll let `deserialize_any()` raise the error
+        }
+    }
+
+    fn deserialize_u8<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value {
+            FieldValue::Int64(v) => {
+                visitor.visit_u8(v.try_into().map_err(<Self::Error as de::Error>::custom)?)
+            }
+            FieldValue::Uint64(v) => {
+                visitor.visit_u8(v.try_into().map_err(<Self::Error as de::Error>::custom)?)
+            }
+            _ => self.deserialize_any(visitor), // we'll let `deserialize_any()` raise the error
+        }
+    }
+
+    fn deserialize_u16<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value {
+            FieldValue::Int64(v) => {
+                visitor.visit_u16(v.try_into().map_err(<Self::Error as de::Error>::custom)?)
+            }
+            FieldValue::Uint64(v) => {
+                visitor.visit_u16(v.try_into().map_err(<Self::Error as de::Error>::custom)?)
+            }
+            _ => self.deserialize_any(visitor), // we'll let `deserialize_any()` raise the error
+        }
+    }
+
+    fn deserialize_u32<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value {
+            FieldValue::Int64(v) => {
+                visitor.visit_u32(v.try_into().map_err(<Self::Error as de::Error>::custom)?)
+            }
+            FieldValue::Uint64(v) => {
+                visitor.visit_u32(v.try_into().map_err(<Self::Error as de::Error>::custom)?)
+            }
+            _ => self.deserialize_any(visitor), // we'll let `deserialize_any()` raise the error
+        }
+    }
+
+    fn deserialize_f32<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value {
+            FieldValue::Float64(v) => visitor.visit_f32(v as f32),
+            _ => self.deserialize_any(visitor), // we'll let `deserialize_any()` raise the error
+        }
+    }
+
+    fn deserialize_tuple<V>(self, len: usize, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        if let FieldValue::List(v) = &self.value {
+            if len != v.len() {
+                return Err(Self::Error::Custom(format!(
+                    "cannot deserialize {} length list into {len} sized tuple",
+                    v.len()
+                )));
+            }
+        }
+        self.deserialize_any(visitor)
+    }
+
+    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        match &self.value {
+            &FieldValue::Null => visitor.visit_none(),
+            _ => visitor.visit_some(self),
+        }
+    }
+
+    fn deserialize_ignored_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_none()
+    }
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value {
+            FieldValue::Null => visitor.visit_none(),
+            FieldValue::Int64(v) => visitor.visit_i64(v),
+            FieldValue::Uint64(v) => visitor.visit_u64(v),
+            FieldValue::Float64(v) => visitor.visit_f64(v),
+            FieldValue::String(v) => visitor.visit_string(v),
+            FieldValue::Boolean(v) => visitor.visit_bool(v),
+            FieldValue::DateTimeUtc(_) => todo!(),
+            FieldValue::Enum(_) => todo!(),
+            FieldValue::List(v) => visitor.visit_seq(v.into_deserializer()),
+        }
+    }
+
+    serde::forward_to_deserialize_any! {
+        bool i64 i128 u64 u128 f64 char str string seq
+        bytes byte_buf unit unit_struct newtype_struct
+        tuple_struct map enum struct identifier
+    }
+}

trustfall_core/src/serialization/mod.rs

@@ -0,0 +1,64 @@
+use std::{collections::BTreeMap, sync::Arc};
+
+use serde::de;
+
+use crate::ir::FieldValue;
+
+mod deserializers;
+
+#[cfg(test)]
+mod tests;
+
+/// Deserialize Trustfall query results into a Rust struct.
+///
+/// ```rust
+/// # use std::{collections::BTreeMap, sync::Arc};
+/// # use maplit::btreemap;
+/// # use trustfall_core::ir::FieldValue;
+/// #
+/// # fn run_query() -> Result<Box<dyn Iterator<Item = BTreeMap<Arc<str>, FieldValue>>>, ()> {
+/// #     Ok(Box::new(vec![
+/// #        btreemap! {
+/// #           Arc::from("number") => FieldValue::Int64(42),
+/// #           Arc::from("text") => FieldValue::String("the answer to everything".to_string()),
+/// #        }
+/// #     ].into_iter()))
+/// # }
+///
+/// use trustfall_core::TryIntoStruct;
+///
+/// #[derive(Debug, PartialEq, Eq, serde::Deserialize)]
+/// struct Output {
+///     number: i64,
+///     text: String,
+/// }
+///
+/// let results: Vec<_> = run_query()
+///     .expect("bad query arguments")
+///     .map(|v| v.try_into_struct().expect("struct definition did not match query result shape"))
+///     .collect();
+///
+/// assert_eq!(
+///     vec![
+///         Output {
+///             number: 42,
+///             text: "the answer to everything".to_string(),
+///         },
+///     ],
+///     results,
+/// );
+/// ```
+pub trait TryIntoStruct {
+    type Error;
+
+    fn try_into_struct<S: for<'de> de::Deserialize<'de>>(self) -> Result<S, Self::Error>;
+}
+
+impl TryIntoStruct for BTreeMap<Arc<str>, FieldValue> {
+    type Error = deserializers::Error;
+
+    fn try_into_struct<S: for<'de> de::Deserialize<'de>>(self) -> Result<S, deserializers::Error> {
+        let deserializer = deserializers::QueryResultDeserializer::new(self);
+        S::deserialize(deserializer)
+    }
+}