Add changelog

CHANGELOG.md

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+Change log
+==========
+
+## 0.6.0 – Unreleased
+
+TL;DR: Many big changes in how context types work and how they
+interact with the executor. Not too much to worry about if you're only
+using the macros and not deriving `GraphQLType` directly.
+
+### Breaking changes
+
+* The `executor` argument in all resolver methods is now
+  immutable. The executor instead uses interior mutability to store
+  errors in a thread-safe manner.
+
+  This change could open up for asynchronous or multi-threaded
+  execution: you can today use something like rayon in your resolve
+  methods to let child nodes be concurrently resolved.
+
+  **How to fix:** All field resolvers that looked like `field
+   name(&mut executor` now should say `field name(&executor`.
+
+* The context type of `GraphQLType` is moved to an associated type;
+  meaning it's no longer generic. This only affects people who
+  implement the trait manually, _not_ macro users.
+
+  This greatly simplifies a lot of code by ensuring that there only
+  can be one `GraphQLType` implementation for any given Rust
+  type. However, it has the downside that support for generic contexts
+  previously used in scalars, has been removed. Instead, use the new
+  context conversion features to accomplish the same task.
+
+  **How to fix:** Instead of `impl GraphQLType<MyContext> for ...`,
+   you use `impl GraphQLType for ... { type Context = MyContext;`.
+
+* All context types must derive the `Context` marker trait. This is
+  part of an overarching change to allow different types to use
+  different contexts.
+
+  **How to fix:** If you have written e.g. `graphql_object!(MyType:
+   MyContext ...)` you will need to add `impl Context for MyContext
+   {}`. Simple as that.
+
+
+### Added
+
+* Support for different contexts for different types. As GraphQL
+  schemas tend to get large, narrowing down the context type to
+  exactly what a given type needs is great for
+  encapsulation. Similarly, letting different subsystems use different
+  resources thorugh the context is also useful for the same reasons.
+
+  Juniper supports two different methods of doing this, depending on
+  your needs: if you have two contexts where one can be converted into
+  the other _without any extra knowledge_, you can implement the new
+  `FromContext` trait. This is useful if you have multiple crates or
+  modules that all belong to the same GraphQL schema:
+
+  ```rust
+
+  struct TopContext {
+    db: DatabaseConnection,
+    session: WebSession,
+    current_user: User,
+  }
+
+  struct ModuleOneContext {
+    db: DatabaseConnection, // This module only requires a database connection
+  }
+
+  impl Context for TopContext {}
+  impl Context for ModuleOneContext {}
+
+  impl FromContext<TopContext> for ModuleOneContext {
+    fn from(ctx: &TopContext) -> ModuleOneContext {
+      ModuleOneContext {
+        db: ctx.db.clone()
+      }
+    }
+  }
+
+  graphql_object!(Query: TopContext |&self| {
+    field item(&executor) -> Item {
+      executor.context().db.get_item()
+    }
+  });
+
+  // The `Item` type uses another context type - conversion is automatic
+  graphql_object!(Item: ModuleOneContext |&self| {
+    // ...
+  });
+
+  ```
+
+  The other way is to manually perform the conversion in a field
+  resolver. This method is preferred when the child context needs
+  extra knowledge than what exists in the parent context:
+
+  ```rust
+
+  // Each entity has its own context
+  struct TopContext {
+    entities: HashMap<i64, EntityContext>,
+    db: DatabaseConnection,
+  }
+
+  struct EntityContext {
+    // fields
+  }
+
+  impl Context for TopContext {}
+  impl Context for EntityContext {}
+
+  graphql_object!(Query: TopContext |&self| {
+    // By returning a tuple (&Context, GraphQLType), you can tell the executor
+    // to switch out the context for the returned value. You can wrap the
+    // tuple in Option<>, FieldResult<>, FieldResult<Option<>>, or just return
+    // the tuple without wrapping it.
+    field entity(&executor, key: i64) -> Option<(&EntityContext, Entity)> {
+      executor.context().entities.get(&key)
+        .map(|ctx| (ctx, executor.context().db.get_entity(key)))
+    }
+  });
+
+  graphql_object!(Entity: EntityContext |&self| {
+    // ...
+  });
+
+  ```
+
+## [0.5.3] – 2016-12-05
+
+### Added
+
+* `jtry!`: Helper macro to produce `FieldResult`s from regular
+  `Result`s. Wherever you would be using `try!` in a regular function
+  or method, you can use `jtry!` in a field resolver:
+
+  ```rust
+  graphql_object(MyType: Database |&self| {
+    field count(&executor) -> FieldResult<i64> {
+      let txn = jtry!(executor.context().transaction());
+
+      let count = jtry!(txn.execute("SELECT COUNT(*) FROM user"));
+
+      Ok(count[0][0])
+    }
+  });
+  ```
+
+### Changes
+
+* Relax context type trait requirements for the iron handler: your
+  contexts no longer have to be `Send + Sync`.
+
+* `RootNode` is now `Send` and `Sync` if both the mutation and query
+  types implement `Send` and `Sync`.
+
+### Bugfixes
+
+* `return` statements inside field resolvers no longer cause syntax
+  errors.
+
+
+
+## 0.5.2 – 2016-11-13
+
+### Added
+
+* Support for marking fields and enum values deprecated.
+* `input_object!` helper macro
+
+### Changes
+
+* The included example server now uses the simple Star Wars schema
+  used in query/introspection tests.
+
+### Bugfixes
+
+* The query validators - particularly ones concerned with validation
+  of input data and variables - have been improved significantly. A
+  large number of test cases have been added.
+
+* Macro syntax stability has also been improved. All syntactical edge
+  cases of the macros have gotten tests to verify their correctness.
+
+
+[0.5.3]: https://github.com/mhallin/juniper/compare/0.5.2...0.5.3