Merge pull request #2966 from dtolnay/noserdecore

Enforce derive cannot be used against serde_core

serde/Cargo.toml

@@ -34,14 +34,6 @@ rustdoc-args = [
     "--extern-html-root-url=std=https://doc.rust-lang.org",
 ]
 
-# This cfg cannot be enabled, but it still forces Cargo to keep serde_derive's
-# version in lockstep with serde's, even if someone depends on the two crates
-# separately with serde's "derive" feature disabled. Every serde_derive release
-# is compatible with exactly one serde release because the generated code
-# involves nonpublic APIs which are not bound by semver.
-[target.'cfg(any())'.dependencies]
-serde_derive = { version = "=1.0.219", path = "../serde_derive" }
-
 
 ### FEATURES #################################################################
 

serde/src/lib.rs

@@ -256,3 +256,9 @@ extern crate serde_derive;
 #[cfg(feature = "serde_derive")]
 #[cfg_attr(docsrs, doc(cfg(feature = "derive")))]
 pub use serde_derive::{Deserialize, Serialize};
+
+#[macro_export]
+#[doc(hidden)]
+macro_rules! __require_serde_not_serde_core {
+    () => {};
+}

serde_core/Cargo.toml

@@ -29,6 +29,14 @@ rustdoc-args = [
     "--extern-html-root-url=std=https://doc.rust-lang.org",
 ]
 
+# This cfg cannot be enabled, but it still forces Cargo to keep serde_derive's
+# version in lockstep with serde's, even if someone depends on the two crates
+# separately with serde's "derive" feature disabled. Every serde_derive release
+# is compatible with exactly one serde release because the generated code
+# involves nonpublic APIs which are not bound by semver.
+[target.'cfg(any())'.dependencies]
+serde_derive = { version = "=1.0.219", path = "../serde_derive" }
+
 
 ### FEATURES #################################################################
 

serde_core/src/lib.rs

@@ -266,3 +266,13 @@ mod seed;
 
 #[cfg(all(not(feature = "std"), no_core_error))]
 mod std_error;
+
+#[macro_export]
+#[doc(hidden)]
+macro_rules! __require_serde_not_serde_core {
+    () => {
+        ::core::compile_error!(
+            "Serde derive requires a dependency on the serde crate, not serde_core"
+        );
+    };
+}

serde_derive/src/dummy.rs

@@ -22,6 +22,9 @@ pub fn wrap_in_const(serde_path: Option<&syn::Path>, code: TokenStream) -> Token
         )]
         const _: () = {
             #use_serde
+
+            _serde::__require_serde_not_serde_core!();
+
             #code
         };
     }