Merge pull request #820 from serde-rs/reexport

Re-export derives from serde

serde/Cargo.toml

@@ -17,6 +17,7 @@ travis-ci = { repository = "serde-rs/serde" }
 
 [features]
 default = ["std"]
+derive = ["serde_derive"]
 
 std = []
 unstable = []

serde/src/lib.rs

@@ -106,3 +106,50 @@ mod utils;
 // Generated code uses these to support no_std. Not public API.
 #[doc(hidden)]
 pub mod export;
+
+// Re-export #[derive(Serialize, Deserialize)].
+//
+// This is a workaround for https://github.com/rust-lang/cargo/issues/1286.
+// Without this re-export, crates that put Serde derives behind a cfg_attr would
+// need to use some silly feature name that depends on both serde and
+// serde_derive.
+//
+//     [features]
+//     serde-impls = ["serde", "serde_derive"]
+//
+//     [dependencies]
+//     serde = { version = "1.0", optional = true }
+//     serde_derive = { version = "1.0", optional = true }
+//
+//     # Used like this:
+//     # #[cfg(feature = "serde-impls")]
+//     # #[macro_use]
+//     # extern crate serde_derive;
+//     #
+//     # #[cfg_attr(feature = "serde-impls", derive(Serialize, Deserialize))]
+//     # struct S { /* ... */ }
+//
+// The re-exported derives allow crates to use "serde" as the name of their
+// Serde feature which is more intuitive.
+//
+//     [dependencies]
+//     serde = { version = "1.0", optional = true, features = ["derive"] }
+//
+//     # Used like this:
+//     # #[cfg(feature = "serde")]
+//     # #[macro_use]
+//     # extern crate serde;
+//     #
+//     # #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+//     # struct S { /* ... */ }
+//
+// The reason re-exporting is not enabled by default is that disabling it would
+// be annoying for crates that provide handwritten impls or data formats. They
+// would need to disable default features and then explicitly re-enable std.
+#[cfg(feature = "serde_derive")]
+#[allow(unused_imports)]
+#[macro_use]
+extern crate serde_derive;
+#[cfg(feature = "serde_derive")]
+#[doc(hidden)]
+pub use serde_derive::*;