Seal `Deserialize` trait

Fixes #81

2 files changed, 9 insertions, 2 deletions

diff --git a/serde_dhall/src/lib.rs b/serde_dhall/src/lib.rs
index 2863788..d8a94d1 100644
--- a/serde_dhall/src/lib.rs
+++ b/serde_dhall/src/lib.rs
@@ -179,6 +179,8 @@ pub mod value {
         }
     }
 
+    impl super::de::sealed::Sealed for Value {}
+
     impl super::de::Deserialize for Value {
         fn from_dhall(v: &Value) -> Result<Self> {
             Ok(v.clone())
@@ -225,14 +227,17 @@ pub mod de {
         }
     }
 
+    pub(crate) mod sealed {
+        pub trait Sealed {}
+    }
+
     /// A data structure that can be deserialized from a Dhall expression
     ///
     /// This is automatically implemented for any type that [serde][serde]
     /// can deserialize.
     ///
     /// This trait cannot be implemented manually.
-    // TODO: seal trait
-    pub trait Deserialize: Sized {
+    pub trait Deserialize: sealed::Sealed + Sized {
         /// See [serde_dhall::from_str][crate::from_str]
         fn from_dhall(v: &Value) -> Result<Self>;
     }
diff --git a/serde_dhall/src/serde.rs b/serde_dhall/src/serde.rs
index cf5efc4..99b9014 100644
--- a/serde_dhall/src/serde.rs
+++ b/serde_dhall/src/serde.rs
@@ -6,6 +6,8 @@ use dhall::syntax::ExprKind;
 use crate::de::{Deserialize, Error, Result};
 use crate::Value;
 
+impl<'a, T> crate::de::sealed::Sealed for T where T: serde::Deserialize<'a> {}
+
 impl<'a, T> Deserialize for T
 where
     T: serde::Deserialize<'a>,