Add ScalarValue::downcast_type() method for GraphQLScalar parsing optimization (#1329, #819)

- rename `TryScalarValueTo` trait as `TryToPrimitive`
- introduce `FromScalarValue` conversion trait
- generate `FromScalarValue` impls in `#[derive(GraphQLScalar)]` and `#[graphql_scalar]` macro expansions
- rebase `ScalarValue::downcast_type()` method to `FromScalarValue` trait

Author: tyranron

book/src/types/scalars.md

@@ -115,7 +115,7 @@ impl UserId {
     /// Checks whether the [`InputValue`] is a [`String`] beginning with `id: ` and strips it.
     fn from_input(
         input: &str,
-        //     ^^^^ any concrete type having `TryScalarValueTo` implementation could be used
+        //     ^^^^ any concrete type having `FromScalarValue` implementation could be used
     ) -> Result<Self, Box<str>> {
     //                ^^^^^^^^ must implement `IntoFieldError`
         input
@@ -145,7 +145,7 @@ impl UserId {
         //      ^^^^^^ for generic argument using `Scalar` transparent wrapper is required,
         //             otherwise Rust won't be able to infer the required type
     ) -> Self {
-    //   ^^^^ if the result is infallible, it's OK to not use `Result`
+    //   ^^^^ if the result is infallible, it's OK to omit `Result`
         Self(
             input
                 .try_to_int().map(|i| i.to_string())

juniper/CHANGELOG.md

@@ -71,17 +71,18 @@ All user visible changes to `juniper` crate will be documented in this file. Thi
     - Removed `as_float_value()`, `as_string_value()` and `as_scalar_value()` methods (use `as_scalar()` method and then `ScalarValue` methods instead).
 - `InputValue` enum: ([#1327])
     - Removed `as_float_value()`, `as_int_value()`, `as_string_value()` and `as_scalar_value()` methods (use `as_scalar()` method and then `ScalarValue` methods instead).
-- `ScalarValue` trait: ([#1327])
-    - Switched from `From` conversions to `TryScalarValueTo` conversions.
-    - Made to require `TryScalarValueTo` conversions for `bool`, `f64`, `i32`, `String` and `&str` types (could be derived with `#[value(<conversion>)]` attributes of `#[derive(ScalarValue)]` macro).
-    - Made to require `TryInto<String>` conversion (could be derived with `derive_more::TryInto`).
-    - Made `is_type()` method required and to accept `Any` type.
-    - Renamed `as_bool()` method as `try_to_bool()` and made it defined by default as `TryScalarValueTo<bool>` alias.
-    - Renamed `as_float()` method as `try_to_float()` and made it defined by default as `TryScalarValueTo<f64>` alias.
-    - Renamed `as_int()` method as `try_to_int()` and made it defined by default as `TryScalarValueTo<i32>` alias.
-    - Renamed `as_string()` method as `try_to_string()` and made it defined by default as `TryScalarValueTo<String>` alias.
-    - Renamed `as_str()` method as `try_as_str()` and made it defined by default as `TryScalarValueTo<&str>` alias.
-    - Renamed `into_string()` method as `try_into_string()` and made it defined by default as `TryInto<String>` alias.
+- `ScalarValue` trait:
+    - Switched from `From` conversions to `TryToPrimitive` and `FromScalarValue` conversions. ([#1327], [#1329])
+    - Made to require `TryToPrimitive` conversions for `bool`, `f64`, `i32`, `String` and `&str` types (could be derived with `#[value(<conversion>)]` attributes of `#[derive(ScalarValue)]` macro). ([#1327], [#1329])
+    - Made to require `TryInto<String>` conversion (could be derived with `derive_more::TryInto`). ([#1327])
+    - Made `is_type()` method required and to accept `Any` type. ([#1327])
+    - Renamed `as_bool()` method as `try_to_bool()` and made it defined by default as `TryToPrimitive<bool>` alias. ([#1327])
+    - Renamed `as_float()` method as `try_to_float()` and made it defined by default as `TryToPrimitive<f64>` alias. ([#1327])
+    - Renamed `as_int()` method as `try_to_int()` and made it defined by default as `TryToPrimitive<i32>` alias. ([#1327])
+    - Renamed `as_string()` method as `try_to_string()` and made it defined by default as `TryToPrimitive<String>` alias. ([#1327])
+    - Renamed `as_str()` method as `try_as_str()` and made it defined by default as `TryToPrimitive<&str>` alias. ([#1327])
+    - Renamed `into_string()` method as `try_into_string()` and made it defined by default as `TryInto<String>` alias. ([#1327])
+    - Required new `downcast_type::<T>()` method (could be derived with `#[derive(ScalarValue)]` macro). ([#1329])
 - `#[derive(ScalarValue)]` macro: ([#1327])
     - Renamed `#[value(as_bool)]` attribute as `#[value(to_bool)]`.
     - Renamed `#[value(as_float)]` attribute as `#[value(to_float)]`.
@@ -90,9 +91,9 @@ All user visible changes to `juniper` crate will be documented in this file. Thi
     - Removed `#[value(into_string)]` attribute.
     - Removed `#[value(allow_missing_attributes)]` attribute (now attributes can always be omitted).
     - `From` and `Display` implementations are not derived anymore (recommended way is to use [`derive_more` crate] for this).
-- `#[derive(GraphQLScalar)]` and `#[graphql_scalar]` macros: ([#1327])
-    - Made provided `from_input()` function to accept `ScalarValue` (or anything `TryScalarValueTo`-convertible) directly instead of `InputValue`.
-- Removed `LocalBoxFuture` usage from `http::tests::WsIntegration` trait. ([todo])
+- `#[derive(GraphQLScalar)]` and `#[graphql_scalar]` macros:
+    - Made provided `from_input()` function to accept `ScalarValue` (or anything `FromScalarValue`-convertible) directly instead of `InputValue`. ([#1327])
+- Removed `LocalBoxFuture` usage from `http::tests::WsIntegration` trait. ([4b14c015])
 
 ### Added
 
@@ -109,14 +110,16 @@ All user visible changes to `juniper` crate will be documented in this file. Thi
 - `String` scalar implementation for `arcstr::ArcStr`. ([#1247])
 - `String` scalar implementation for `compact_str::CompactString`. ([20609366])
 - `IntoValue` and `IntoInputValue` conversion traits allowing to work around orphan rules with custom `ScalarValue`. ([#1324])
+- `FromScalarValue` conversion trait. ([#1329])
+- `TryToPrimitive` conversion trait aiding `ScalarValue` trait. ([#1327], [#1329])
 - `ScalarValue` trait:
     - `from_displayable()` method allowing to specialize `ScalarValue` conversion from custom string types. ([#1324], [#819])
-    - `try_to::<T>()` method defined by default as `TryScalarValueTo<T>` alias. ([#1327])
-- `TryScalarValueTo` conversion trait aiding `ScalarValue` trait. ([#1327])
-- `#[derive(GraphQLScalar)]` and `#[graphql_scalar]` macros: ([#1327])
-    - Support for specifying concrete types as input argument in provided `from_input()` function.
-    - Support for non-`Result` return type in provided `from_input()` function.
-    - `Scalar` transparent wrapper for aiding type inference in `from_input()` function when input argument is generic `ScalarValue`.
+    - `try_to::<T>()` method defined by default as `FromScalarValue<T>` alias. ([#1327], [#1329])
+- `#[derive(GraphQLScalar)]` and `#[graphql_scalar]` macros:
+    - Support for specifying concrete types as input argument in provided `from_input()` function. ([#1327])
+    - Support for non-`Result` return type in provided `from_input()` function. ([#1327])
+    - `Scalar` transparent wrapper for aiding type inference in `from_input()` function when input argument is generic `ScalarValue`. ([#1327])
+    - Generating of `FromScalarValue` implementation. ([#1329])
 
 ### Changed
 
@@ -144,9 +147,10 @@ All user visible changes to `juniper` crate will be documented in this file. Thi
 [#1324]: /../../pull/1324
 [#1326]: /../../pull/1326
 [#1327]: /../../pull/1327
+[#1329]: /../../pull/1329
 [1b1fc618]: /../../commit/1b1fc61879ffdd640d741e187dc20678bf7ab295
 [20609366]: /../../commit/2060936635609b0186d46d8fbd06eb30fce660e3
-[todo]: /../../commit/todo
+[4b14c015]: /../../commit/4b14c015018d31cb6df848efdee24d96416b76d9
 
 
 

juniper/src/ast.rs

@@ -200,24 +200,18 @@ pub type Document<'a, S> = [Definition<'a, S>];
 #[doc(hidden)]
 pub type OwnedDocument<'a, S> = Vec<Definition<'a, S>>;
 
-/// Parsing of an unstructured input value into a Rust data type.
+/// Parsing of an unstructured [`InputValue`] into a Rust data type.
 ///
-/// The conversion _can_ fail, and must in that case return [`Err`]. Thus not
-/// restricted in the definition of this trait, the returned [`Err`] should be
-/// convertible with [`IntoFieldError`] to fit well into the library machinery.
+/// The conversion _can_ fail, and must in that case return an [`Err`]. Thus, not restricted in the
+/// definition of this trait, the returned [`Err`] should be convertible with the [`IntoFieldError`]
+/// trait to fit well into the library machinery.
 ///
-/// Implemented automatically by the convenience proc macro [`graphql_scalar!`]
-/// or by deriving `GraphQLEnum`.
-///
-/// Must be implemented manually when manually exposing new enums or scalars.
-///
-/// [`graphql_scalar!`]: macro@crate::graphql_scalar
 /// [`IntoFieldError`]: crate::IntoFieldError
 pub trait FromInputValue<S = DefaultScalarValue>: Sized {
     /// Type of this conversion error.
     ///
-    /// Thus not restricted, it should be convertible with [`IntoFieldError`] to
-    /// fit well into the library machinery.
+    /// Thus, not restricted, it should be convertible with the [`IntoFieldError`] trait to fit well
+    /// into the library machinery.
     ///
     /// [`IntoFieldError`]: crate::IntoFieldError
     type Error;
@@ -615,13 +609,13 @@ impl<'a, S> VariableDefinitions<'a, S> {
 }
 
 #[cfg(test)]
-mod tests {
+mod spec_input_value_fmt {
     use crate::graphql_input_value;
 
     use super::InputValue;
 
     #[test]
-    fn test_input_value_fmt() {
+    fn correct() {
         let value: InputValue = graphql_input_value!(null);
         assert_eq!(value.to_string(), "null");
 

juniper/src/lib.rs

@@ -103,8 +103,8 @@ pub use crate::{
     },
     validation::RuleError,
     value::{
-        AnyExt, DefaultScalarValue, IntoValue, Object, ParseScalarResult, ParseScalarValue, Scalar,
-        ScalarValue, TryScalarValueTo, Value, WrongInputScalarTypeError,
+        AnyExt, DefaultScalarValue, FromScalarValue, IntoValue, Object, ParseScalarResult,
+        ParseScalarValue, Scalar, ScalarValue, TryToPrimitive, Value, WrongInputScalarTypeError,
     },
 };
 

juniper/src/types/pointers.rs

@@ -11,7 +11,7 @@ use crate::{
         async_await::GraphQLValueAsync,
         base::{Arguments, GraphQLType, GraphQLValue},
     },
-    value::ScalarValue,
+    value::{FromScalarValue, ScalarValue},
 };
 
 impl<S, T> GraphQLType<S> for Box<T>
@@ -87,6 +87,18 @@ where
     }
 }
 
+impl<'s, T, S> FromScalarValue<'s, S> for Box<T>
+where
+    S: ScalarValue,
+    T: FromScalarValue<'s, S> + 's,
+{
+    type Error = T::Error;
+
+    fn from_scalar_value(v: &'s S) -> Result<Self, Self::Error> {
+        T::from_scalar_value(v).map(Self::new)
+    }
+}
+
 impl<T, S> FromInputValue<S> for Box<T>
 where
     S: ScalarValue,
@@ -275,6 +287,18 @@ where
     }
 }
 
+impl<'s, T, S> FromScalarValue<'s, S> for Arc<T>
+where
+    S: ScalarValue,
+    T: FromScalarValue<'s, S> + 's,
+{
+    type Error = T::Error;
+
+    fn from_scalar_value(v: &'s S) -> Result<Self, Self::Error> {
+        T::from_scalar_value(v).map(Self::new)
+    }
+}
+
 impl<T, S> FromInputValue<S> for Arc<T>
 where
     S: ScalarValue,

juniper/src/types/scalars.rs

@@ -1,10 +1,10 @@
-use std::{char, convert::identity, marker::PhantomData, rc::Rc, thread::JoinHandle};
+use std::{char, marker::PhantomData, rc::Rc, thread::JoinHandle};
 
 use derive_more::with_trait::{Deref, Display, From, Into};
 use serde::{Deserialize, Serialize};
 
 use crate::{
-    GraphQLScalar, Scalar,
+    GraphQLScalar, IntoFieldError, Scalar,
     ast::{InputValue, Selection, ToInputValue},
     executor::{ExecutionResult, Executor, Registry},
     graphql_scalar,
@@ -16,7 +16,10 @@ use crate::{
         base::{GraphQLType, GraphQLValue},
         subscriptions::GraphQLSubscriptionValue,
     },
-    value::{ParseScalarResult, ScalarValue, Value, WrongInputScalarTypeError},
+    value::{
+        FromScalarValue, ParseScalarResult, ScalarValue, TryToPrimitive, Value,
+        WrongInputScalarTypeError,
+    },
 };
 
 /// An ID as defined by the GraphQL specification
@@ -56,12 +59,23 @@ impl ID {
 }
 
 #[graphql_scalar]
-#[graphql(with = impl_string_scalar, from_input_with = identity::<String>)]
+#[graphql(with = impl_string_scalar, from_input_with = __builtin)]
 type String = std::string::String;
 
 mod impl_string_scalar {
     use super::*;
 
+    impl<'s, S> FromScalarValue<'s, S> for String
+    where
+        S: TryToPrimitive<'s, Self, Error: IntoFieldError<S>> + 's,
+    {
+        type Error = S::Error;
+
+        fn from_scalar_value(v: &'s S) -> Result<Self, Self::Error> {
+            v.try_to_primitive()
+        }
+    }
+
     pub(super) fn to_output<S: ScalarValue>(v: &str) -> Value<S> {
         Value::scalar(v.to_owned())
     }
@@ -176,14 +190,20 @@ type ArcStr = arcstr::ArcStr;
 
 mod impl_arcstr_scalar {
     use super::ArcStr;
-    use crate::{IntoValue as _, ScalarValue, Value};
+    use crate::{FromScalarValue, IntoValue as _, Scalar, ScalarValue, Value};
 
     pub(super) fn to_output<S: ScalarValue>(v: &ArcStr) -> Value<S> {
         v.into_value()
     }
 
-    pub(super) fn from_input(s: &str) -> ArcStr {
-        s.into()
+    pub(super) fn from_input<S: ScalarValue>(
+        v: &Scalar<S>,
+    ) -> Result<ArcStr, <&str as FromScalarValue<'_, S>>::Error> {
+        if let Some(s) = v.downcast_type::<ArcStr>() {
+            Ok(s.clone())
+        } else {
+            v.try_to::<&str>().map(ArcStr::from)
+        }
     }
 }
 
@@ -193,14 +213,20 @@ type CompactString = compact_str::CompactString;
 
 mod impl_compactstring_scalar {
     use super::CompactString;
-    use crate::{IntoValue as _, ScalarValue, Value};
+    use crate::{FromScalarValue, IntoValue as _, Scalar, ScalarValue, Value};
 
     pub(super) fn to_output<S: ScalarValue>(v: &CompactString) -> Value<S> {
         v.into_value()
     }
 
-    pub(super) fn from_input(s: &str) -> CompactString {
-        s.into()
+    pub(super) fn from_input<S: ScalarValue>(
+        v: &Scalar<S>,
+    ) -> Result<CompactString, <&str as FromScalarValue<'_, S>>::Error> {
+        if let Some(s) = v.downcast_type::<CompactString>() {
+            Ok(s.clone())
+        } else {
+            v.try_to::<&str>().map(CompactString::from)
+        }
     }
 }
 
@@ -274,13 +300,35 @@ where
     }
 }
 
+impl<'s, S> FromScalarValue<'s, S> for &'s str
+where
+    S: TryToPrimitive<'s, Self, Error: IntoFieldError<S>> + 's,
+{
+    type Error = S::Error;
+
+    fn from_scalar_value(v: &'s S) -> Result<Self, Self::Error> {
+        v.try_to_primitive()
+    }
+}
+
 #[graphql_scalar]
-#[graphql(with = impl_boolean_scalar, from_input_with = identity::<Boolean>)]
+#[graphql(with = impl_boolean_scalar, from_input_with = __builtin)]
 type Boolean = bool;
 
 mod impl_boolean_scalar {
     use super::*;
 
+    impl<'s, S> FromScalarValue<'s, S> for Boolean
+    where
+        S: TryToPrimitive<'s, Self, Error: IntoFieldError<S>> + 's,
+    {
+        type Error = S::Error;
+
+        fn from_scalar_value(v: &'s S) -> Result<Self, Self::Error> {
+            v.try_to_primitive()
+        }
+    }
+
     pub(super) fn to_output<S: ScalarValue>(v: &Boolean) -> Value<S> {
         Value::scalar(*v)
     }
@@ -292,12 +340,23 @@ mod impl_boolean_scalar {
 }
 
 #[graphql_scalar]
-#[graphql(with = impl_int_scalar, from_input_with = identity::<Int>)]
+#[graphql(with = impl_int_scalar, from_input_with = __builtin)]
 type Int = i32;
 
 mod impl_int_scalar {
     use super::*;
 
+    impl<'s, S> FromScalarValue<'s, S> for Int
+    where
+        S: TryToPrimitive<'s, Self, Error: IntoFieldError<S>> + 's,
+    {
+        type Error = S::Error;
+
+        fn from_scalar_value(v: &'s S) -> Result<Self, Self::Error> {
+            v.try_to_primitive()
+        }
+    }
+
     pub(super) fn to_output<S: ScalarValue>(v: &Int) -> Value<S> {
         Value::scalar(*v)
     }
@@ -314,12 +373,23 @@ mod impl_int_scalar {
 }
 
 #[graphql_scalar]
-#[graphql(with = impl_float_scalar, from_input_with = identity::<Float>)]
+#[graphql(with = impl_float_scalar, from_input_with = __builtin)]
 type Float = f64;
 
 mod impl_float_scalar {
     use super::*;
 
+    impl<'s, S> FromScalarValue<'s, S> for Float
+    where
+        S: TryToPrimitive<'s, Self, Error: IntoFieldError<S>> + 's,
+    {
+        type Error = S::Error;
+
+        fn from_scalar_value(v: &'s S) -> Result<Self, Self::Error> {
+            v.try_to_primitive()
+        }
+    }
+
     pub(super) fn to_output<S: ScalarValue>(v: &Float) -> Value<S> {
         Value::scalar(*v)
     }

juniper/src/value/mod.rs

@@ -10,8 +10,8 @@ pub(crate) use self::scalar::ScalarValueFmt;
 pub use self::{
     object::Object,
     scalar::{
-        AnyExt, DefaultScalarValue, ParseScalarResult, ParseScalarValue, Scalar, ScalarValue,
-        TryScalarValueTo, WrongInputScalarTypeError,
+        AnyExt, DefaultScalarValue, FromScalarValue, ParseScalarResult, ParseScalarValue, Scalar,
+        ScalarValue, TryToPrimitive, WrongInputScalarTypeError,
     },
 };
 use crate::{