Include the Rust type name in WrongType

Author: sfackler

tokio-postgres/src/row.rs

@@ -164,7 +164,10 @@ impl Row {
 
         let ty = self.columns()[idx].type_();
         if !T::accepts(ty) {
-            return Err(Error::from_sql(Box::new(WrongType::new(ty.clone())), idx));
+            return Err(Error::from_sql(
+                Box::new(WrongType::new::<T>(ty.clone())),
+                idx,
+            ));
         }
 
         let buf = self.ranges[idx].clone().map(|r| &self.body.buffer()[r]);

tokio-postgres/src/types/mod.rs

@@ -68,7 +68,7 @@ where
     T: ToSql,
 {
     if !T::accepts(ty) {
-        return Err(Box::new(WrongType(ty.clone())));
+        return Err(Box::new(WrongType::new::<T>(ty.clone())));
     }
     v.to_sql(ty, out)
 }
@@ -91,6 +91,7 @@ mod type_gen;
 
 #[cfg(feature = "with-serde_json-1")]
 pub use crate::types::serde_json_1::Json;
+use std::any::type_name;
 
 /// A Postgres type.
 #[derive(PartialEq, Eq, Clone, Debug)]
@@ -206,23 +207,29 @@ impl Error for WasNull {}
 /// An error indicating that a conversion was attempted between incompatible
 /// Rust and Postgres types.
 #[derive(Debug)]
-pub struct WrongType(Type);
+pub struct WrongType {
+    postgres: Type,
+    rust: &'static str,
+}
 
 impl fmt::Display for WrongType {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(
             fmt,
-            "cannot convert to or from a Postgres value of type `{}`",
-            self.0
+            "cannot convert between the Rust type `{}` and the Postgres type `{}`",
+            self.rust, self.postgres,
         )
     }
 }
 
 impl Error for WrongType {}
 
 impl WrongType {
-    pub(crate) fn new(ty: Type) -> WrongType {
-        WrongType(ty)
+    pub(crate) fn new<T>(ty: Type) -> WrongType {
+        WrongType {
+            postgres: ty,
+            rust: type_name::<T>(),
+        }
     }
 }