(codegen) Implement newtype derive for scalars.

This commit implements a newtype style custom derive
for scalars via `#[derive(GraphQLScalarValue)]`, which now
supports both deriving a base enum scalar type and newtypes.

For newtypes, the `#[graphql(transparent)]` attribute is
required.

This commit:
* implements the derive
* adds integration tests
* updates the book

Author: theduke

docs/book/content/types/scalars.md

@@ -6,59 +6,131 @@ but this often requires coordination with the client library intended to consume
 the API you're building.
 
 Since any value going over the wire is eventually transformed into JSON, you're
-also limited in the data types you can use. Typically, you represent your custom
-scalars as strings.
+also limited in the data types you can use. 
 
-In Juniper, you use the `graphql_scalar!` macro to create a custom scalar. In
-this example, we're representing a user ID as a string wrapped in a custom type:
+There are two ways to define custom scalars. 
+* For simple scalars that just wrap a primitive type, you can use the newtype pattern with
+a custom derive. 
+* For more advanced use cases with custom validation, you can use
+the `graphql_scalar!` macro.
 
-```rust
-use juniper::Value;
 
-struct UserID(String);
+## Built-in scalars
 
-juniper::graphql_scalar!(UserID where Scalar = <S> {
-    description: "An opaque identifier, represented as a string"
+Juniper has built-in support for:
 
-    resolve(&self) -> Value {
-        Value::scalar(self.0.clone())
-    }
+* `i32` as `Int`
+* `f64` as `Float`
+* `String` and `&str` as `String`
+* `bool` as `Boolean`
+* `juniper::ID` as `ID`. This type is defined [in the
+  spec](http://facebook.github.io/graphql/#sec-ID) as a type that is serialized
+  as a string but can be parsed from both a string and an integer.
 
-    from_input_value(v: &InputValue) -> Option<UserID> {
-        // If there's a parse error here, simply return None. Juniper will
-        // present an error to the client.
-        v.as_scalar_value::<String>().map(|s| UserID(s.to_owned()))
-    }
+**Third party types**:
 
-    from_str<'a>(value: ScalarToken<'a>) -> juniper::ParseScalarResult<'a, S> {
-        <String as juniper::ParseScalarValue<S>>::from_str(value)
-    }
-});
+Juniper has built-in support for a few additional types from common third party
+crates. They are enabled via features that are on by default.
+
+* uuid::Uuid
+* chrono::DateTime
+* url::Url
+
+## newtype pattern
+
+Often, you might need a custom scalar that just wraps an existing type. 
+
+This can be done with the newtype pattern and a custom derive, similar to how
+serde supports this pattern with `#[transparent]`.
+
+```rust
+#[derive(juniper::GraphQLScalarValue)]
+#[graphql(transparent)]
+pub struct UserId(i32);
 
 #[derive(juniper::GraphQLObject)]
 struct User {
-    id: UserID,
-    username: String,
+    id: UserId,
 }
 
 # fn main() {}
 ```
 
-## Built-in scalars
+That's it, you can now user `UserId` in your schema.
 
-Juniper has built-in support for:
+The macro also allows for more customization:
 
-* `i32` as `Int`
-* `f64` as `Float`
-* `String` and `&str` as `String`
-* `bool` as `Boolean`
-* `juniper::ID` as `ID`. This type is defined [in the
-  spec](http://facebook.github.io/graphql/#sec-ID) as a type that is serialized
-  as a string but can be parsed from both a string and an integer.
+```rust
+/// You can use a doc comment to specify a description.
+#[derive(juniper::GraphQLScalarValue)]
+#[graphql(
+    transparent,
+    // Overwrite the GraphQL type name.
+    name = "MyUserId",
+    // Specify a custom description.
+    // A description in the attribute will overwrite a doc comment.
+    description = "My user id description",
+)]
+pub struct UserId(i32);
+
+# fn main() {}
+```
+
+## Custom scalars
+
+For more complex situations where you also need custom parsing or validation, 
+you can use the `graphql_scalar!` macro.
+
+Typically, you represent your custom scalars as strings.
+
+The example below implements a custom scalar for a custom `Date` type.
+
+Note: juniper already has built-in support for the `chrono::DateTime` type 
+via `chrono` feature, which is enabled by default and should be used for this 
+purpose.
 
-### Non-standard scalars
+The example below is used just for illustration.
 
-Juniper has built-in support for UUIDs from the [uuid
-crate](https://doc.rust-lang.org/uuid/uuid/index.html). This support is enabled
-by default, but can be disabled if you want to reduce the number of dependencies
-in your application.
+**Note**: the example assumes that the `Date` type implements
+`std::fmt::Display` and `std::str::FromStr`.
+
+
+```rust
+# mod date { 
+#    pub struct Date; 
+#    impl std::str::FromStr for Date{ 
+#        type Err = String; fn from_str(_value: &str) -> Result<Self, Self::Err> { unimplemented!() }
+#    }
+#    // And we define how to represent date as a string.
+#    impl std::fmt::Display for Date {
+#        fn fmt(&self, _f: &mut std::fmt::Formatter) -> std::fmt::Result {
+#            unimplemented!()
+#        }
+#    }
+# }
+
+use juniper::{Value, ParseScalarResult, ParseScalarValue};
+use date::Date;
+
+juniper::graphql_scalar!(Date where Scalar = <S> {
+    description: "Date"
+
+    // Define how to convert your custom scalar into a primitive type.
+    resolve(&self) -> Value {
+        Value::scalar(self.to_string())
+    }
+
+    // Define how to parse a primitive type into your custom scalar.
+    from_input_value(v: &InputValue) -> Option<Date> {
+        v.as_scalar_value::<String>()
+         .and_then(|s| s.parse().ok())
+    }
+
+    // Define how to parse a string value.
+    from_str<'a>(value: ScalarToken<'a>) -> ParseScalarResult<'a, S> {
+        <String as ParseScalarValue<S>>::from_str(value)
+    }
+});
+
+# fn main() {}
+```

docs/book/tests/Cargo.toml

@@ -9,11 +9,12 @@ build = "build.rs"
 juniper = { path = "../../../juniper" }
 juniper_iron = { path = "../../../juniper_iron" }
 
-iron = "^0.5.0"
-mount = "^0.3.0"
+iron = "0.5.0"
+mount = "0.4.0"
 
 skeptic = "0.13"
 serde_json = "1.0.39"
+uuid = "0.7.4"
 
 [build-dependencies]
 skeptic = "0.13"

integration_tests/juniper_tests/src/codegen/derive_input_object.rs

@@ -1,4 +1,3 @@
-#[cfg(test)]
 use fnv::FnvHashMap;
 
 use juniper::DefaultScalarValue;

integration_tests/juniper_tests/src/codegen/mod.rs

@@ -3,3 +3,4 @@ mod util;
 mod derive_enum;
 mod derive_input_object;
 mod derive_object;
+mod scalar_value_transparent;

integration_tests/juniper_tests/src/codegen/scalar_value_transparent.rs

@@ -0,0 +1,76 @@
+use fnv::FnvHashMap;
+use juniper::{DefaultScalarValue, FromInputValue, GraphQLType, InputValue, ToInputValue};
+
+#[derive(juniper::GraphQLScalarValue, PartialEq, Eq, Debug)]
+#[graphql(transparent)]
+struct UserId(String);
+
+#[derive(juniper::GraphQLScalarValue, PartialEq, Eq, Debug)]
+#[graphql(transparent, name = "MyUserId", description = "custom description...")]
+struct CustomUserId(String);
+
+/// The doc comment...
+#[derive(juniper::GraphQLScalarValue, PartialEq, Eq, Debug)]
+#[graphql(transparent)]
+struct IdWithDocComment(i32);
+
+#[derive(juniper::GraphQLObject)]
+struct User {
+    id: UserId,
+    id_custom: CustomUserId,
+}
+
+struct User2;
+
+#[juniper::object]
+impl User2 {
+    fn id(&self) -> UserId {
+        UserId("id".to_string())
+    }
+}
+
+#[test]
+fn test_scalar_value_simple() {
+    assert_eq!(<UserId as GraphQLType>::name(&()), Some("UserId"));
+
+    let mut registry: juniper::Registry = juniper::Registry::new(FnvHashMap::default());
+    let meta = UserId::meta(&(), &mut registry);
+    assert_eq!(meta.name(), Some("UserId"));
+    assert_eq!(meta.description(), None);
+
+    let input: InputValue = serde_json::from_value(serde_json::json!("userId1")).unwrap();
+    let output: UserId = FromInputValue::from_input_value(&input).unwrap();
+    assert_eq!(output, UserId("userId1".into()),);
+
+    let id = UserId("111".into());
+    let output = ToInputValue::<DefaultScalarValue>::to_input_value(&id);
+    assert_eq!(output, InputValue::scalar("111"),);
+}
+
+#[test]
+fn test_scalar_value_custom() {
+    assert_eq!(<CustomUserId as GraphQLType>::name(&()), Some("MyUserId"));
+
+    let mut registry: juniper::Registry = juniper::Registry::new(FnvHashMap::default());
+    let meta = CustomUserId::meta(&(), &mut registry);
+    assert_eq!(meta.name(), Some("MyUserId"));
+    assert_eq!(
+        meta.description(),
+        Some(&"custom description...".to_string())
+    );
+
+    let input: InputValue = serde_json::from_value(serde_json::json!("userId1")).unwrap();
+    let output: CustomUserId = FromInputValue::from_input_value(&input).unwrap();
+    assert_eq!(output, CustomUserId("userId1".into()),);
+
+    let id = CustomUserId("111".into());
+    let output = ToInputValue::<DefaultScalarValue>::to_input_value(&id);
+    assert_eq!(output, InputValue::scalar("111"),);
+}
+
+#[test]
+fn test_scalar_value_doc_comment() {
+    let mut registry: juniper::Registry = juniper::Registry::new(FnvHashMap::default());
+    let meta = IdWithDocComment::meta(&(), &mut registry);
+    assert_eq!(meta.description(), Some(&"The doc comment...".to_string()));
+}

juniper/CHANGELOG.md

@@ -1,5 +1,23 @@
 # master
 
+### newtype ScalarValue derive
+
+See [#345](https://github.com/graphql-rust/juniper/pull/345).
+
+The newtype pattern can now be used with the `GraphQLScalarValue` custom derive
+to easily implement custom scalar values that just wrap another scalar, 
+similar to serdes `#[transparent]` functionality.
+
+Example:
+
+```rust
+#[derive(juniper::GraphQLScalarValue)]
+#[graphql(transparent)]
+struct UserId(i32);
+```
+
+### Other Changes
+
 - The `ID` scalar now implements Serde's `Serialize` and `Deserialize`
 
 # [[0.12.0] 2019-05-16](https://github.com/graphql-rust/juniper/releases/tag/juniper-0.12.0)