fix unions with custom scalar values

integration_tests/codegen_fail/fail/union/enum_non_object_variant.stderr

@@ -1,12 +1,3 @@
-error[E0277]: the trait bound `Test: juniper::types::marker::GraphQLObjectType<juniper::value::scalar::DefaultScalarValue>` is not satisfied
- --> $DIR/enum_non_object_variant.rs:9:10
-  |
-9 | #[derive(GraphQLUnion)]
-  |          ^^^^^^^^^^^^ the trait `juniper::types::marker::GraphQLObjectType<juniper::value::scalar::DefaultScalarValue>` is not implemented for `Test`
-  |
-  = note: required by `juniper::types::marker::GraphQLObjectType::mark`
-  = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)
-
 error[E0277]: the trait bound `Test: juniper::types::marker::GraphQLObjectType<__S>` is not satisfied
  --> $DIR/enum_non_object_variant.rs:9:10
   |

integration_tests/codegen_fail/fail/union/enum_same_type_ugly.stderr

@@ -1,4 +1,4 @@
-error[E0119]: conflicting implementations of trait `<Character as juniper::types::marker::GraphQLUnion>::mark::_::{{closure}}#0::MutuallyExclusive` for type `std::string::String`:
+error[E0119]: conflicting implementations of trait `<Character as juniper::types::marker::GraphQLUnion<__S>>::mark::_::{{closure}}#0::MutuallyExclusive` for type `std::string::String`:
  --> $DIR/enum_same_type_ugly.rs:3:10
   |
 3 | #[derive(GraphQLUnion)]

integration_tests/codegen_fail/fail/union/struct_non_object_variant.stderr

@@ -1,12 +1,3 @@
-error[E0277]: the trait bound `Test: juniper::types::marker::GraphQLObjectType<juniper::value::scalar::DefaultScalarValue>` is not satisfied
- --> $DIR/struct_non_object_variant.rs:9:10
-  |
-9 | #[derive(GraphQLUnion)]
-  |          ^^^^^^^^^^^^ the trait `juniper::types::marker::GraphQLObjectType<juniper::value::scalar::DefaultScalarValue>` is not implemented for `Test`
-  |
-  = note: required by `juniper::types::marker::GraphQLObjectType::mark`
-  = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)
-
 error[E0277]: the trait bound `Test: juniper::types::marker::GraphQLObjectType<__S>` is not satisfied
  --> $DIR/struct_non_object_variant.rs:9:10
   |

integration_tests/codegen_fail/fail/union/struct_same_type_ugly.stderr

@@ -1,4 +1,4 @@
-error[E0119]: conflicting implementations of trait `<Character as juniper::types::marker::GraphQLUnion>::mark::_::{{closure}}#0::MutuallyExclusive` for type `std::string::String`:
+error[E0119]: conflicting implementations of trait `<Character as juniper::types::marker::GraphQLUnion<__S>>::mark::_::{{closure}}#0::MutuallyExclusive` for type `std::string::String`:
  --> $DIR/struct_same_type_ugly.rs:3:10
   |
 3 | #[derive(GraphQLUnion)]

integration_tests/codegen_fail/fail/union/trait_non_object_variant.stderr

@@ -1,12 +1,3 @@
-error[E0277]: the trait bound `Test: juniper::types::marker::GraphQLObjectType<juniper::value::scalar::DefaultScalarValue>` is not satisfied
- --> $DIR/trait_non_object_variant.rs:9:1
-  |
-9 | #[graphql_union]
-  | ^^^^^^^^^^^^^^^^ the trait `juniper::types::marker::GraphQLObjectType<juniper::value::scalar::DefaultScalarValue>` is not implemented for `Test`
-  |
-  = note: required by `juniper::types::marker::GraphQLObjectType::mark`
-  = note: this error originates in an attribute macro (in Nightly builds, run with -Z macro-backtrace for more info)
-
 error[E0277]: the trait bound `Test: juniper::types::marker::GraphQLObjectType<__S>` is not satisfied
  --> $DIR/trait_non_object_variant.rs:9:1
   |

integration_tests/codegen_fail/fail/union/trait_same_type_ugly.stderr

@@ -1,4 +1,4 @@
-error[E0119]: conflicting implementations of trait `<(dyn Character + std::marker::Send + std::marker::Sync + '__obj) as juniper::types::marker::GraphQLUnion>::mark::_::{{closure}}#0::MutuallyExclusive` for type `std::string::String`:
+error[E0119]: conflicting implementations of trait `<(dyn Character + std::marker::Send + std::marker::Sync + '__obj) as juniper::types::marker::GraphQLUnion<__S>>::mark::_::{{closure}}#0::MutuallyExclusive` for type `std::string::String`:
  --> $DIR/trait_same_type_ugly.rs:3:1
   |
 3 | #[graphql_union]

integration_tests/juniper_tests/src/codegen/union_attr.rs

@@ -556,6 +556,97 @@ mod explicit_scalar {
     }
 }
 
+mod custom_scalar {
+    use crate::custom_scalar::MyScalarValue;
+
+    use super::*;
+
+    #[graphql_union(scalar = MyScalarValue)]
+    trait Character {
+        fn as_human(&self) -> Option<&Human> {
+            None
+        }
+        fn as_droid(&self) -> Option<&Droid> {
+            None
+        }
+    }
+
+    impl Character for Human {
+        fn as_human(&self) -> Option<&Human> {
+            Some(&self)
+        }
+    }
+
+    impl Character for Droid {
+        fn as_droid(&self) -> Option<&Droid> {
+            Some(&self)
+        }
+    }
+
+    type DynCharacter<'a> = dyn Character + Send + Sync + 'a;
+
+    enum QueryRoot {
+        Human,
+        Droid,
+    }
+
+    #[graphql_object(scalar = MyScalarValue)]
+    impl QueryRoot {
+        fn character(&self) -> Box<DynCharacter<'_>> {
+            let ch: Box<DynCharacter<'_>> = match self {
+                Self::Human => Box::new(Human {
+                    id: "human-32".to_string(),
+                    home_planet: "earth".to_string(),
+                }),
+                Self::Droid => Box::new(Droid {
+                    id: "droid-99".to_string(),
+                    primary_function: "run".to_string(),
+                }),
+            };
+            ch
+        }
+    }
+
+    const DOC: &str = r#"{
+        character {
+            ... on Human {
+                humanId: id
+                homePlanet
+            }
+            ... on Droid {
+                droidId: id
+                primaryFunction
+            }
+        }
+    }"#;
+
+    #[tokio::test]
+    async fn resolves_human() {
+        let schema = schema::<_, MyScalarValue, _>(QueryRoot::Human);
+
+        assert_eq!(
+            execute(DOC, None, &schema, &Variables::new(), &()).await,
+            Ok((
+                graphql_value!({"character": {"humanId": "human-32", "homePlanet": "earth"}}),
+                vec![],
+            )),
+        );
+    }
+
+    #[tokio::test]
+    async fn resolves_droid() {
+        let schema = schema::<_, MyScalarValue, _>(QueryRoot::Droid);
+
+        assert_eq!(
+            execute(DOC, None, &schema, &Variables::new(), &()).await,
+            Ok((
+                graphql_value!({"character": {"droidId": "droid-99", "primaryFunction": "run"}}),
+                vec![],
+            )),
+        );
+    }
+}
+
 mod inferred_custom_context {
     use super::*;
 

integration_tests/juniper_tests/src/codegen/union_derive.rs

@@ -485,6 +485,79 @@ mod explicit_scalar {
     }
 }
 
+mod custom_scalar {
+    use crate::custom_scalar::MyScalarValue;
+
+    use super::*;
+
+    #[derive(GraphQLUnion)]
+    #[graphql(scalar = MyScalarValue)]
+    enum Character {
+        A(Human),
+        B(Droid),
+    }
+
+    enum QueryRoot {
+        Human,
+        Droid,
+    }
+
+    #[graphql_object(scalar = MyScalarValue)]
+    impl QueryRoot {
+        fn character(&self) -> Character {
+            match self {
+                Self::Human => Character::A(Human {
+                    id: "human-32".to_string(),
+                    home_planet: "earth".to_string(),
+                }),
+                Self::Droid => Character::B(Droid {
+                    id: "droid-99".to_string(),
+                    primary_function: "run".to_string(),
+                }),
+            }
+        }
+    }
+
+    const DOC: &str = r#"{
+        character {
+            ... on Human {
+                humanId: id
+                homePlanet
+            }
+            ... on Droid {
+                droidId: id
+                primaryFunction
+            }
+        }
+    }"#;
+
+    #[tokio::test]
+    async fn resolves_human() {
+        let schema = schema::<_, MyScalarValue, _>(QueryRoot::Human);
+
+        assert_eq!(
+            execute(DOC, None, &schema, &Variables::new(), &()).await,
+            Ok((
+                graphql_value!({"character": {"humanId": "human-32", "homePlanet": "earth"}}),
+                vec![],
+            )),
+        );
+    }
+
+    #[tokio::test]
+    async fn resolves_droid() {
+        let schema = schema::<_, MyScalarValue, _>(QueryRoot::Droid);
+
+        assert_eq!(
+            execute(DOC, None, &schema, &Variables::new(), &()).await,
+            Ok((
+                graphql_value!({"character": {"droidId": "droid-99", "primaryFunction": "run"}}),
+                vec![],
+            )),
+        );
+    }
+}
+
 mod custom_context {
     use super::*;
 

integration_tests/juniper_tests/src/custom_scalar.rs

@@ -10,7 +10,7 @@ use juniper::{
 use std::fmt;
 
 #[derive(Debug, Clone, PartialEq, juniper::GraphQLScalarValue)]
-enum MyScalarValue {
+pub(crate) enum MyScalarValue {
     Int(i32),
     Long(i64),
     Float(f64),
@@ -59,7 +59,7 @@ impl ScalarValue for MyScalarValue {
 }
 
 #[derive(Default, Debug)]
-struct MyScalarValueVisitor;
+pub(crate) struct MyScalarValueVisitor;
 
 impl<'de> de::Visitor<'de> for MyScalarValueVisitor {
     type Value = MyScalarValue;

juniper/src/types/marker.rs

@@ -37,7 +37,7 @@ pub trait GraphQLObjectType<S: ScalarValue>: GraphQLType<S> {
 /// [4]: https://spec.graphql.org/June2018/#sec-Objects
 /// [5]: https://spec.graphql.org/June2018/#sec-Input-Objects
 /// [6]: https://spec.graphql.org/June2018/#sec-Interfaces
-pub trait GraphQLUnion: GraphQLType {
+pub trait GraphQLUnion<S: ScalarValue>: GraphQLType<S> {
     /// An arbitrary function without meaning.
     ///
     /// May contain compile timed check logic which ensures that types are used correctly according

juniper_codegen/src/graphql_union/mod.rs

@@ -414,11 +414,6 @@ impl ToTokens for UnionDefinition {
             .as_ref()
             .map(|scl| quote! { #scl })
             .unwrap_or_else(|| quote! { __S });
-        let default_scalar = self
-            .scalar
-            .as_ref()
-            .map(|scl| quote! { #scl })
-            .unwrap_or_else(|| quote! { #crate_path::DefaultScalarValue });
 
         let description = self
             .description
@@ -493,13 +488,10 @@ impl ToTokens for UnionDefinition {
 
         let (_, ty_generics, _) = self.generics.split_for_impl();
 
-        let mut base_generics = self.generics.clone();
+        let mut ext_generics = self.generics.clone();
         if self.is_trait_object {
-            base_generics.params.push(parse_quote! { '__obj });
+            ext_generics.params.push(parse_quote! { '__obj });
         }
-        let (impl_generics, _, _) = base_generics.split_for_impl();
-
-        let mut ext_generics = base_generics.clone();
         if self.scalar.is_none() {
             ext_generics.params.push(parse_quote! { #scalar });
             ext_generics
@@ -618,13 +610,13 @@ impl ToTokens for UnionDefinition {
 
         let union_impl = quote! {
             #[automatically_derived]
-            impl#impl_generics #crate_path::marker::GraphQLUnion for #ty_full {
+            impl#ext_impl_generics #crate_path::marker::GraphQLUnion<#scalar> for #ty_full
+                #where_clause
+            {
                 fn mark() {
                     #all_variants_unique
 
-                    #( <#var_types as #crate_path::marker::GraphQLObjectType<
-                        #default_scalar,
-                    >>::mark(); )*
+                    #( <#var_types as #crate_path::marker::GraphQLObjectType<#scalar>>::mark(); )*
                 }
             }
         };