Input Object Type Validation 2021 Spec

https://spec.graphql.org/June2018/#sec-Input-Objects

Type Validation

1. An Input Object type must define one or more input fields.
2. For each input field of an Input Object type
   a. The input field must have a unique name within that Input Object type; no two input fields may share the same name.
   b. The input field must not have a name which begins with the characters "__" (two underscores).
3. The input field must accept a type where IsInputType(inputFieldType) returns true.

Already Implemented:

1. https://github.com/ChilliCream/hotchocolate/blob/c1eb36cf3542572372847c5e38f4bc349bc22bfa/src/HotChocolate/Core/src/Types/Types/FieldCollection.cs#L58

2. b. https://github.com/ChilliCream/hotchocolate/blob/c1eb36cf3542572372847c5e38f4bc349bc22bfa/src/HotChocolate/Core/src/Types/Configuration/Validation/ComplexOutputTypeValidationHelper.cs#L37