Add ability to distinguish between implicit and explicit null (#795)

* add Nullable to distinguish between implicit and explicit null

* cargo fmt

* add page to book

* address comment

docs/book/content/SUMMARY.md

@@ -29,6 +29,7 @@
 
   - [Introspection](advanced/introspection.md)
   - [Non-struct objects](advanced/non_struct_objects.md)
+  - [Implicit and explicit null](advanced/implicit_and_explicit_null.md)
   - [Objects and generics](advanced/objects_and_generics.md)
   - [Multiple operations per request](advanced/multiple_ops_per_request.md)
   - [Dataloaders](advanced/dataloaders.md)

docs/book/content/advanced/implicit_and_explicit_null.md

@@ -0,0 +1,116 @@
+# Implicit and explicit null
+
+There are two ways that a client can submit a null argument or field in a query.
+
+They can use a null literal:
+
+```graphql
+{
+    field(arg: null)
+}
+```
+
+Or they can simply omit the argument:
+
+```graphql
+{
+    field
+}
+```
+
+The former is an explicit null and the latter is an implicit null.
+
+There are some situations where it's useful to know which one the user provided.
+
+For example, let's say your business logic has a function that allows users to
+perform a "patch" operation on themselves. Let's say your users can optionally
+have favorite and least favorite numbers, and the input for that might look
+like this:
+
+```rust
+/// Updates user attributes. Fields that are `None` are left as-is.
+pub struct UserPatch {
+    /// If `Some`, updates the user's favorite number.
+    pub favorite_number: Option<Option<i32>>,
+
+    /// If `Some`, updates the user's least favorite number.
+    pub least_favorite_number: Option<Option<i32>>,
+}
+
+# fn main() {}
+```
+
+To set a user's favorite number to 7, you would set `favorite_number` to
+`Some(Some(7))`. In GraphQL, that might look like this:
+
+```graphql
+mutation { patchUser(patch: { favoriteNumber: 7 }) }
+```
+
+To unset the user's favorite number, you would set `favorite_number` to
+`Some(None)`. In GraphQL, that might look like this:
+
+```graphql
+mutation { patchUser(patch: { favoriteNumber: null }) }
+```
+
+If you want to leave the user's favorite number alone, you would set it to
+`None`. In GraphQL, that might look like this:
+
+```graphql
+mutation { patchUser(patch: {}) }
+```
+
+The last two cases rely on being able to distinguish between explicit and implicit null.
+
+In Juniper, this can be done using the `Nullable` type:
+
+```rust
+# extern crate juniper;
+use juniper::{FieldResult, Nullable};
+
+#[derive(juniper::GraphQLInputObject)]
+struct UserPatchInput {
+    pub favorite_number: Nullable<i32>,
+    pub least_favorite_number: Nullable<i32>,
+}
+
+impl Into<UserPatch> for UserPatchInput {
+    fn into(self) -> UserPatch {
+        UserPatch {
+            // The `explicit` function transforms the `Nullable` into an
+            // `Option<Option<T>>` as expected by the business logic layer.
+            favorite_number: self.favorite_number.explicit(),
+            least_favorite_number: self.least_favorite_number.explicit(),
+        }
+    }
+}
+
+# pub struct UserPatch {
+#     pub favorite_number: Option<Option<i32>>,
+#     pub least_favorite_number: Option<Option<i32>>,
+# }
+
+# struct Session;
+# impl Session {
+#     fn patch_user(&self, _patch: UserPatch) -> FieldResult<()> { Ok(()) }
+# }
+
+struct Context {
+    session: Session,
+}
+
+struct Mutation;
+
+#[juniper::graphql_object(Context=Context)]
+impl Mutation {
+    fn patch_user(ctx: &Context, patch: UserPatchInput) -> FieldResult<bool> {
+        ctx.session.patch_user(patch.into())?;
+        Ok(true)
+    }
+}
+# fn main() {}
+```
+
+This type functions much like `Option`, but has two empty variants so you can
+distinguish between implicit and explicit null.

docs/book/content/advanced/index.md

@@ -4,6 +4,7 @@ The chapters below cover some more advanced scenarios.
 
 - [Introspection](introspection.md)
 - [Non-struct objects](non_struct_objects.md)
+- [Implicit and explicit null](implicit_and_explicit_null.md)
 - [Objects and generics](objects_and_generics.md)
 - [Multiple operations per request](multiple_ops_per_request.md)
 - [Dataloaders](dataloaders.md)

integration_tests/juniper_tests/src/explicit_null.rs

@@ -0,0 +1,81 @@
+use juniper::*;
+
+pub struct Context;
+
+impl juniper::Context for Context {}
+
+pub struct Query;
+
+#[derive(juniper::GraphQLInputObject)]
+struct ObjectInput {
+    field: Nullable<i32>,
+}
+
+#[graphql_object(Context=Context)]
+impl Query {
+    fn is_explicit_null(arg: Nullable<i32>) -> bool {
+        arg.is_explicit_null()
+    }
+
+    fn object_field_is_explicit_null(obj: ObjectInput) -> bool {
+        obj.field.is_explicit_null()
+    }
+}
+
+type Schema = juniper::RootNode<'static, Query, EmptyMutation<Context>, EmptySubscription<Context>>;
+
+#[tokio::test]
+async fn explicit_null() {
+    let ctx = Context;
+
+    let query = r#"
+    query Foo($emptyObj: ObjectInput!, $literalNullObj: ObjectInput!) {
+        literalOneIsExplicitNull: isExplicitNull(arg: 1)
+        literalNullIsExplicitNull: isExplicitNull(arg: null)
+        noArgIsExplicitNull: isExplicitNull
+        literalOneFieldIsExplicitNull: objectFieldIsExplicitNull(obj: {field: 1})
+        literalNullFieldIsExplicitNull: objectFieldIsExplicitNull(obj: {field: null})
+        noFieldIsExplicitNull: objectFieldIsExplicitNull(obj: {})
+        emptyVariableObjectFieldIsExplicitNull: objectFieldIsExplicitNull(obj: $emptyObj)
+        literalNullVariableObjectFieldIsExplicitNull: objectFieldIsExplicitNull(obj: $literalNullObj)
+    }
+    "#;
+
+    let (data, errors) = juniper::execute(
+        query,
+        None,
+        &Schema::new(
+            Query,
+            EmptyMutation::<Context>::new(),
+            EmptySubscription::<Context>::new(),
+        ),
+        &[
+            ("emptyObj".to_string(), InputValue::Object(vec![])),
+            (
+                "literalNullObj".to_string(),
+                InputValue::object(vec![("field", InputValue::null())].into_iter().collect()),
+            ),
+        ]
+        .iter()
+        .cloned()
+        .collect(),
+        &ctx,
+    )
+    .await
+    .unwrap();
+
+    assert_eq!(errors.len(), 0);
+    assert_eq!(
+        data,
+        graphql_value!({
+            "literalOneIsExplicitNull": false,
+            "literalNullIsExplicitNull": true,
+            "noArgIsExplicitNull": false,
+            "literalOneFieldIsExplicitNull": false,
+            "literalNullFieldIsExplicitNull": true,
+            "noFieldIsExplicitNull": false,
+            "emptyVariableObjectFieldIsExplicitNull": false,
+            "literalNullVariableObjectFieldIsExplicitNull": true,
+        })
+    );
+}

integration_tests/juniper_tests/src/lib.rs

@@ -5,6 +5,8 @@ mod codegen;
 #[cfg(test)]
 mod custom_scalar;
 #[cfg(test)]
+mod explicit_null;
+#[cfg(test)]
 mod issue_371;
 #[cfg(test)]
 mod issue_398;

juniper/CHANGELOG.md

@@ -35,6 +35,8 @@
   
 - Support `chrono-tz::Tz` scalar behind a `chrono-tz` feature flag. ([#519](https://github.com/graphql-rust/juniper/pull/519))
 
+- Added support for distinguishing between between implicit and explicit null. ([#795](https://github.com/graphql-rust/juniper/pull/795))
+  
 ## Fixes
 
 - Massively improved the `#[graphql_union]` proc macro. ([#666](https://github.com/graphql-rust/juniper/pull/666)):

juniper/src/ast.rs

@@ -153,6 +153,14 @@ pub type Document<'a, S> = Vec<Definition<'a, S>>;
 pub trait FromInputValue<S = DefaultScalarValue>: Sized {
     /// Performs the conversion.
     fn from_input_value(v: &InputValue<S>) -> Option<Self>;
+
+    /// Performs the conversion from an absent value (e.g. to distinguish between implicit and
+    /// explicit null). The default implementation just uses `from_input_value` as if an explicit
+    /// null were provided. This conversion must not fail.
+    fn from_implicit_null() -> Self {
+        Self::from_input_value(&InputValue::<S>::Null)
+            .expect("input value conversion from null must not fail")
+    }
 }
 
 /// Losslessly clones a Rust data type into an InputValue.

juniper/src/lib.rs

@@ -169,6 +169,7 @@ pub use crate::{
         async_await::{DynGraphQLValueAsync, GraphQLTypeAsync, GraphQLValueAsync},
         base::{Arguments, DynGraphQLValue, GraphQLType, GraphQLValue, TypeKind},
         marker::{self, GraphQLInterface, GraphQLUnion},
+        nullable::Nullable,
         scalars::{EmptyMutation, EmptySubscription, ID},
         subscriptions::{
             ExecutionOutput, GraphQLSubscriptionType, GraphQLSubscriptionValue,

juniper/src/types/base.rs

@@ -91,8 +91,6 @@ where
                 if !args.contains_key(arg.name.as_str()) || args[arg.name.as_str()].is_null() {
                     if let Some(ref default_value) = arg.default_value {
                         args.insert(arg.name.as_str(), default_value.clone());
-                    } else {
-                        args.insert(arg.name.as_str(), InputValue::null());
                     }
                 }
             }

juniper/src/types/mod.rs

@@ -3,6 +3,7 @@ pub mod base;
 pub mod containers;
 pub mod marker;
 pub mod name;
+pub mod nullable;
 pub mod pointers;
 pub mod scalars;
 pub mod subscriptions;

juniper/src/types/nullable.rs

@@ -0,0 +1,328 @@
+use crate::{
+    ast::{FromInputValue, InputValue, Selection, ToInputValue},
+    executor::{ExecutionResult, Executor, Registry},
+    schema::meta::MetaType,
+    types::{
+        async_await::GraphQLValueAsync,
+        base::{GraphQLType, GraphQLValue},
+        marker::IsInputType,
+    },
+    value::{ScalarValue, Value},
+};
+
+/// `Nullable` can be used in situations where you need to distinguish between an implicitly and
+/// explicitly null input value.
+///
+/// The GraphQL spec states that these two field calls are similar, but are not identical:
+///
+/// ```graphql
+/// {
+///   field(arg: null)
+///   field
+/// }
+/// ```
+///
+/// The first has explicitly provided null to the argument “arg”, while the second has implicitly
+/// not provided a value to the argument “arg”. These two forms may be interpreted differently. For
+/// example, a mutation representing deleting a field vs not altering a field, respectively.
+///
+/// In cases where you do not need to be able to distinguish between the two types of null, you
+/// should simply use `Option<T>`.
+#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
+pub enum Nullable<T> {
+    /// No value
+    ImplicitNull,
+    /// No value, explicitly specified to be null
+    ExplicitNull,
+    /// Some value `T`
+    Some(T),
+}
+
+impl<T> Default for Nullable<T> {
+    fn default() -> Self {
+        Self::ImplicitNull
+    }
+}
+
+impl<T> Nullable<T> {
+    /// Returns `true` if the nullable is a `ExplicitNull` value.
+    #[inline]
+    pub fn is_explicit_null(&self) -> bool {
+        match self {
+            Self::ExplicitNull => true,
+            _ => false,
+        }
+    }
+
+    /// Returns `true` if the nullable is a `ImplicitNull` value.
+    #[inline]
+    pub fn is_implicit_null(&self) -> bool {
+        match self {
+            Self::ImplicitNull => true,
+            _ => false,
+        }
+    }
+
+    /// Returns `true` if the nullable is a `Some` value.
+    #[inline]
+    pub fn is_some(&self) -> bool {
+        match self {
+            Self::Some(_) => true,
+            _ => false,
+        }
+    }
+
+    /// Returns `true` if the nullable is not a `Some` value.
+    #[inline]
+    pub fn is_null(&self) -> bool {
+        match self {
+            Self::Some(_) => false,
+            _ => true,
+        }
+    }
+
+    /// Converts from `&mut Nullable<T>` to `Nullable<&mut T>`.
+    #[inline]
+    pub fn as_mut(&mut self) -> Nullable<&mut T> {
+        match *self {
+            Self::Some(ref mut x) => Nullable::Some(x),
+            Self::ImplicitNull => Nullable::ImplicitNull,
+            Self::ExplicitNull => Nullable::ExplicitNull,
+        }
+    }
+
+    /// Returns the contained `Some` value, consuming the `self` value.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the value is not a `Some` with a custom panic message provided by `msg`.
+    #[inline]
+    #[track_caller]
+    pub fn expect(self, msg: &str) -> T {
+        self.some().expect(msg)
+    }
+
+    /// Returns the contained `Some` value or a provided default.
+    #[inline]
+    pub fn unwrap_or(self, default: T) -> T {
+        self.some().unwrap_or(default)
+    }
+
+    /// Returns the contained `Some` value or computes it from a closure.
+    #[inline]
+    pub fn unwrap_or_else<F: FnOnce() -> T>(self, f: F) -> T {
+        self.some().unwrap_or_else(f)
+    }
+
+    /// Maps a `Nullable<T>` to `Nullable<U>` by applying a function to a contained value.
+    #[inline]
+    pub fn map<U, F: FnOnce(T) -> U>(self, f: F) -> Nullable<U> {
+        match self {
+            Self::Some(x) => Nullable::Some(f(x)),
+            Self::ImplicitNull => Nullable::ImplicitNull,
+            Self::ExplicitNull => Nullable::ExplicitNull,
+        }
+    }
+
+    /// Applies a function to the contained value (if any), or returns the provided default (if
+    /// not).
+    #[inline]
+    pub fn map_or<U, F: FnOnce(T) -> U>(self, default: U, f: F) -> U {
+        self.some().map_or(default, f)
+    }
+
+    /// Applies a function to the contained value (if any), or computes a default (if not).
+    #[inline]
+    pub fn map_or_else<U, D: FnOnce() -> U, F: FnOnce(T) -> U>(self, default: D, f: F) -> U {
+        self.some().map_or_else(default, f)
+    }
+
+    /// Transforms the `Nullable<T>` into a `Result<T, E>`, mapping `Some(v)` to `Ok(v)` and
+    /// `ImplicitNull` or `ExplicitNull` to `Err(err)`.
+    #[inline]
+    pub fn ok_or<E>(self, err: E) -> Result<T, E> {
+        self.some().ok_or(err)
+    }
+
+    /// Transforms the `Nullable<T>` into a `Result<T, E>`, mapping `Some(v)` to `Ok(v)` and
+    /// `ImplicitNull` or `ExplicitNull` to `Err(err())`.
+    #[inline]
+    pub fn ok_or_else<E, F: FnOnce() -> E>(self, err: F) -> Result<T, E> {
+        self.some().ok_or_else(err)
+    }
+
+    /// Returns the nullable if it contains a value, otherwise returns `b`.
+    #[inline]
+    pub fn or(self, b: Self) -> Self {
+        match self {
+            Self::Some(_) => self,
+            _ => b,
+        }
+    }
+
+    /// Returns the nullable if it contains a value, otherwise calls `f` and
+    /// returns the result.
+    #[inline]
+    pub fn or_else<F: FnOnce() -> Nullable<T>>(self, f: F) -> Nullable<T> {
+        match self {
+            Self::Some(_) => self,
+            _ => f(),
+        }
+    }
+
+    /// Replaces the actual value in the nullable by the value given in parameter, returning the
+    /// old value if present, leaving a `Some` in its place without deinitializing either one.
+    #[inline]
+    pub fn replace(&mut self, value: T) -> Self {
+        std::mem::replace(self, Self::Some(value))
+    }
+
+    /// Converts from `Nullable<T>` to `Option<T>`.
+    pub fn some(self) -> Option<T> {
+        match self {
+            Self::Some(v) => Some(v),
+            _ => None,
+        }
+    }
+
+    /// Converts from `Nullable<T>` to `Option<Option<T>>`, mapping `Some(v)` to `Some(Some(v))`,
+    /// `ExplicitNull` to `Some(None)`, and `ImplicitNull` to `None`.
+    pub fn explicit(self) -> Option<Option<T>> {
+        match self {
+            Self::Some(v) => Some(Some(v)),
+            Self::ExplicitNull => Some(None),
+            Self::ImplicitNull => None,
+        }
+    }
+}
+
+impl<T: Copy> Nullable<&T> {
+    /// Maps a `Nullable<&T>` to a `Nullable<T>` by copying the contents of the nullable.
+    pub fn copied(self) -> Nullable<T> {
+        self.map(|&t| t)
+    }
+}
+
+impl<T: Copy> Nullable<&mut T> {
+    /// Maps a `Nullable<&mut T>` to a `Nullable<T>` by copying the contents of the nullable.
+    pub fn copied(self) -> Nullable<T> {
+        self.map(|&mut t| t)
+    }
+}
+
+impl<T: Clone> Nullable<&T> {
+    /// Maps a `Nullable<&T>` to a `Nullable<T>` by cloning the contents of the nullable.
+    pub fn cloned(self) -> Nullable<T> {
+        self.map(|t| t.clone())
+    }
+}
+
+impl<T: Clone> Nullable<&mut T> {
+    /// Maps a `Nullable<&mut T>` to a `Nullable<T>` by cloning the contents of the nullable.
+    pub fn cloned(self) -> Nullable<T> {
+        self.map(|t| t.clone())
+    }
+}
+
+impl<S, T> GraphQLType<S> for Nullable<T>
+where
+    T: GraphQLType<S>,
+    S: ScalarValue,
+{
+    fn name(_: &Self::TypeInfo) -> Option<&'static str> {
+        None
+    }
+
+    fn meta<'r>(info: &Self::TypeInfo, registry: &mut Registry<'r, S>) -> MetaType<'r, S>
+    where
+        S: 'r,
+    {
+        registry.build_nullable_type::<T>(info).into_meta()
+    }
+}
+
+impl<S, T> GraphQLValue<S> for Nullable<T>
+where
+    S: ScalarValue,
+    T: GraphQLValue<S>,
+{
+    type Context = T::Context;
+    type TypeInfo = T::TypeInfo;
+
+    fn type_name(&self, _: &Self::TypeInfo) -> Option<&'static str> {
+        None
+    }
+
+    fn resolve(
+        &self,
+        info: &Self::TypeInfo,
+        _: Option<&[Selection<S>]>,
+        executor: &Executor<Self::Context, S>,
+    ) -> ExecutionResult<S> {
+        match *self {
+            Self::Some(ref obj) => executor.resolve(info, obj),
+            _ => Ok(Value::null()),
+        }
+    }
+}
+
+impl<S, T> GraphQLValueAsync<S> for Nullable<T>
+where
+    T: GraphQLValueAsync<S>,
+    T::TypeInfo: Sync,
+    T::Context: Sync,
+    S: ScalarValue + Send + Sync,
+{
+    fn resolve_async<'a>(
+        &'a self,
+        info: &'a Self::TypeInfo,
+        _: Option<&'a [Selection<S>]>,
+        executor: &'a Executor<Self::Context, S>,
+    ) -> crate::BoxFuture<'a, ExecutionResult<S>> {
+        let f = async move {
+            let value = match self {
+                Self::Some(obj) => executor.resolve_into_value_async(info, obj).await,
+                _ => Value::null(),
+            };
+            Ok(value)
+        };
+        Box::pin(f)
+    }
+}
+
+impl<S, T> FromInputValue<S> for Nullable<T>
+where
+    T: FromInputValue<S>,
+    S: ScalarValue,
+{
+    fn from_input_value(v: &InputValue<S>) -> Option<Nullable<T>> {
+        match v {
+            &InputValue::Null => Some(Self::ExplicitNull),
+            v => v.convert().map(Self::Some),
+        }
+    }
+
+    fn from_implicit_null() -> Self {
+        Self::ImplicitNull
+    }
+}
+
+impl<S, T> ToInputValue<S> for Nullable<T>
+where
+    T: ToInputValue<S>,
+    S: ScalarValue,
+{
+    fn to_input_value(&self) -> InputValue<S> {
+        match *self {
+            Self::Some(ref v) => v.to_input_value(),
+            _ => InputValue::null(),
+        }
+    }
+}
+
+impl<S, T> IsInputType<S> for Nullable<T>
+where
+    T: IsInputType<S>,
+    S: ScalarValue,
+{
+}

juniper_codegen/src/impl_object.rs

@@ -46,6 +46,13 @@ fn create(
 
     let top_attrs = &_impl.attrs;
 
+    let scalar = _impl
+        .attrs
+        .scalar
+        .as_ref()
+        .map(|s| quote!( #s ))
+        .unwrap_or_else(|| quote!(::juniper::DefaultScalarValue));
+
     let fields = _impl
         .methods
         .iter()
@@ -87,10 +94,6 @@ fn create(
                                 .apply(&arg_name)
                         });
 
-                    let expect_text = format!(
-                        "Internal error: missing argument {} - validation must have failed",
-                        &final_name
-                    );
                     let mut_modifier = if is_mut { quote!(mut) } else { quote!() };
 
                     if final_name.starts_with("__") {
@@ -109,7 +112,7 @@ fn create(
                     let resolver = quote!(
                         let #mut_modifier #arg_ident = args
                             .get::<#ty>(#final_name)
-                            .expect(#expect_text);
+                            .unwrap_or_else(::juniper::FromInputValue::<#scalar>::from_implicit_null);
                     );
 
                     let field_type = util::GraphQLTypeDefinitionFieldArg {

juniper_codegen/src/util/mod.rs

@@ -1701,7 +1701,10 @@ impl GraphQLTypeDefiniton {
             })
             .collect::<Vec<_>>();
 
-        let from_inputs = self.fields.iter().map(|field| {
+        let from_inputs = self
+            .fields
+            .iter()
+            .map(|field| {
                 let field_ident = &field.resolver_code;
                 let field_name = &field.name;
 
@@ -1721,14 +1724,12 @@ impl GraphQLTypeDefiniton {
                         match obj.get(#field_name) {
                             #from_input_default
                             Some(ref v) => ::juniper::FromInputValue::from_input_value(v).unwrap(),
-                        None => {
+                            None => ::juniper::FromInputValue::<#scalar>::from_implicit_null(),
-                            ::juniper::FromInputValue::from_input_value(&::juniper::InputValue::<#scalar>::null())
-                            .unwrap()
-                        },
                         }
                     },
                 )
-        }).collect::<Vec<_>>();
+            })
+            .collect::<Vec<_>>();
 
         let to_inputs = self
             .fields