Responding to comments

cedar-policy-core/src/entities/json/err.rs

@@ -76,7 +76,7 @@ pub enum JsonDeserializationError {
         got: Box<Either<serde_json::Value, Expr>>,
     },
     /// A field that needs to be an extension value, was some other JSON value
-    #[error("{ctx}, expected an extension value, but got `{got}`")]
+    #[error("{ctx}, expected an extension value, but got `{}`", display_json_value(.got.as_ref()))]
     ExpectedExtnValue {
         /// Context of this error
         ctx: Box<JsonDeserializationErrorContext>,

cedar-policy-core/src/entities/json/value.rs

@@ -484,6 +484,9 @@ impl<'e> ValueParser<'e> {
         ctx: impl Fn() -> JsonDeserializationErrorContext + Clone,
     ) -> Result<RestrictedExpr, JsonDeserializationError> {
         match extnjson {
+            ExtnValueJson::ExplicitExprEscape { __expr } => {
+                Err(JsonDeserializationError::ExprTag(Box::new(ctx())))
+            }
             ExtnValueJson::ExplicitExtnEscape { __extn }
             | ExtnValueJson::ImplicitExtnEscape(__extn) => {
                 // reuse the same logic that parses CedarValueJson
@@ -617,6 +620,8 @@ pub enum EntityUidJson {
 #[derive(Debug, Clone, PartialEq, Eq, Deserialize, Serialize)]
 #[serde(untagged)]
 pub enum ExtnValueJson {
+    /// This was removed in 3.0 as is here to give nice error messages
+    ExplicitExprEscape { __expr: String },
     /// Explicit `__extn` escape; see notes on `CedarValueJson::ExtnEscape`
     ExplicitExtnEscape {
         /// JSON object containing the extension-constructor call

cedar-policy/CHANGELOG.md

@@ -21,7 +21,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Changed
 
 - Removed `__expr` escape from Cedar JSON formats
-<<<<<<< HEAD
 - Rename `cedar_policy_core::est::EstToAstError` to `cedar_policy_core::est::FromJsonError`.
 - Rename `cedar_policy_core::entities::JsonDeserializationError::ExtensionsError` to `cedar_policy_core::entities::JsonDeserializationError::FailedExtensionsFunctionLookup`.
 - Rename variants in `cedar_policy::SchemaError`.