Move serde warning to Environment::new to make it more visible

Author: mitsuhiko

minijinja/src/environment.rs

@@ -85,6 +85,15 @@ impl<'source> Environment<'source> {
     /// the default filters, tests and globals loaded.  If you do not want any
     /// default configuration you can use the alternative
     /// [`empty`](Environment::empty) method.
+    #[cfg_attr(
+        not(feature = "serde"),
+        deprecated(
+            since = "2.0.4",
+            note = "Attempted to instanciate an environment with serde.  Future \
+        versions of MiniJinja will require enabling the 'serde' feature to use \
+        serde types.  To silence this warning add 'serde' to the list of features of minijinja."
+        )
+    )]
     pub fn new() -> Environment<'source> {
         Environment {
             templates: TemplateStore::new(TemplateConfig::new(Arc::new(

minijinja/src/lib.rs

@@ -246,23 +246,6 @@ pub use self::value::Value;
 pub use self::macros::__context;
 pub use self::vm::State;
 
-// forwards compatibility
-#[cfg(not(feature = "serde"))]
-const _: () = {
-    #[deprecated(
-        since = "2.0.4",
-        note = "Future versions of MiniJinja will require enabling \
-        the 'serde' feature to use serde types.  To silence this warning \
-        add 'serde' to the list of features of minijinja."
-    )]
-    #[allow(unused)]
-    fn enable_implicit_serde_support() {}
-
-    fn trigger_warning() {
-        enable_implicit_serde_support();
-    }
-};
-
 /// This module gives access to the low level machinery.
 ///
 /// This module is only provided by the `unstable_machinery` feature and does not