Export codegen from main juniper crate

Use a trick for re-exporting proc-macros to supply juniper_derive as a
dependency of juniper.

Users will now just have to depend on juniper directly.

juniper/Cargo.toml

@@ -20,16 +20,25 @@ harness = false
 path = "benches/bench.rs"
 
 [features]
+codegen = ["juniper_codegen"]
 nightly = []
 expose-test-schema = []
-default = ["chrono", "url", "uuid"]
+default = [
+    "codegen",
+    "chrono",
+    "url",
+    "uuid"
+]
 
 [dependencies]
+juniper_codegen = { version = "0.8.1", path = "../juniper_codegen" , optional = true}
+
 fnv = "1.0.3"
-chrono = { version = "^0.4.0", optional = true }
 ordermap = { version = "^0.2.11", features = ["serde-1"] }
 serde = { version = "^1.0.8" }
 serde_derive = {version="^1.0.8" }
+
+chrono = { version = "^0.4.0", optional = true }
 serde_json = { version="^1.0.2", optional = true }
 url = { version = "^1.5.1", optional = true }
 uuid = { version = "0.5.1", optional = true }

juniper/src/lib.rs

@@ -136,6 +136,17 @@ extern crate url;
 #[cfg(any(test, feature = "uuid"))]
 extern crate uuid;
 
+// If the "codegen" feature is enabled, depend on juniper_codegen and re-export everything in it.
+// This allows users to just depend on juniper and get the derive funcationality automatically.
+#[cfg(feature = "codegen")]
+#[allow(unused_imports)]
+#[macro_use]
+extern crate juniper_codegen;
+
+#[cfg(feature = "codegen")]
+#[doc(hidden)]
+pub use juniper_codegen::*;
+
 use std::borrow::Cow;
 
 #[macro_use]

juniper_codegen/Cargo.toml

@@ -11,8 +11,8 @@ repository = "https://github.com/graphql-rust/juniper"
 proc-macro = true
 
 [dependencies]
-syn = "0.11.11"
-quote = "0.3.15"
+syn = "0.11"
+quote = "0.3"
 
 [badges]
 travis-ci = { repository = "graphql-rust/juniper" }

juniper_tests/Cargo.toml

@@ -4,8 +4,7 @@ version = "0.1.0"
 
 [dependencies]
 juniper = { path = "../juniper" }
-juniper_codegen = { path = "../juniper_codegen" }
-serde_json = { version = "^1.0.2" }
+serde_json = { version = "1" }
 
 [dev-dependencies]
 fnv = "1.0.3"

juniper_tests/src/lib.rs

@@ -1,7 +1,5 @@
 #[macro_use]
 extern crate juniper;
-#[macro_use]
-extern crate juniper_codegen;
 extern crate serde_json;
 
 #[cfg(test)]