[ffe] Expose EvaluationFailure

This is required to allow tracers return more precise error codes.

Author: dd-oleksii

datadog-ffe/src/rules_based/error.rs

@@ -29,7 +29,7 @@ pub enum EvaluationError {
 /// default assignment.
 #[derive(thiserror::Error, Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
 #[serde(rename_all = "SCREAMING_SNAKE_CASE")]
-pub(crate) enum EvaluationFailure {
+pub enum EvaluationFailure {
     /// True evaluation error that should be returned to the user.
     #[error(transparent)]
     Error(EvaluationError),

datadog-ffe/src/rules_based/eval/eval_assignment.rs

@@ -20,13 +20,13 @@ pub fn get_assignment(
     subject: &EvaluationContext,
     expected_type: Option<VariationType>,
     now: DateTime<Utc>,
-) -> Result<Option<Assignment>, EvaluationError> {
+) -> Result<Assignment, EvaluationFailure> {
     let Some(config) = configuration else {
         log::trace!(
             flag_key,
             targeting_key = subject.targeting_key();
             "returning default assignment because of: {}", EvaluationFailure::ConfigurationMissing);
-        return Ok(None);
+        return Err(EvaluationFailure::ConfigurationMissing);
     };
 
     config.eval_flag(flag_key, subject, expected_type, now)
@@ -39,28 +39,26 @@ impl Configuration {
         context: &EvaluationContext,
         expected_type: Option<VariationType>,
         now: DateTime<Utc>,
-    ) -> Result<Option<Assignment>, EvaluationError> {
+    ) -> Result<Assignment, EvaluationFailure> {
         let result = self
             .flags
             .compiled
             .eval_flag(flag_key, context, expected_type, now);
 
-        match result {
+        match &result {
             Ok(assignment) => {
                 log::trace!(
-                flag_key,
-                targeting_key = context.targeting_key(),
-                assignment:serde = assignment.value;
-                "evaluated a flag");
-                Ok(Some(assignment))
+                    flag_key,
+                    targeting_key = context.targeting_key(),
+                    assignment:serde = assignment.value;
+                    "evaluated a flag");
             }
 
             Err(EvaluationFailure::ConfigurationMissing) => {
                 log::warn!(
-                flag_key,
-                targeting_key = context.targeting_key();
-                "evaluating a flag before flags configuration has been fetched");
-                Ok(None)
+                    flag_key,
+                    targeting_key = context.targeting_key();
+                    "evaluating a flag before flags configuration has been fetched");
             }
 
             Err(EvaluationFailure::Error(err)) => {
@@ -69,19 +67,16 @@ impl Configuration {
                     targeting_key = context.targeting_key();
                     "error occurred while evaluating a flag: {err}",
                 );
-                Err(err)
             }
-
-            // Non-Error failures are considered normal conditions and usually don't need extra
-            // attention, so we remap them to Ok(None) before returning to the user.
             Err(err) => {
                 log::trace!(
                     flag_key,
                     targeting_key = context.targeting_key();
                     "returning default assignment because of: {err}");
-                Ok(None)
             }
         }
+
+        result
     }
 }
 
@@ -281,8 +276,7 @@ mod tests {
                     &subject,
                     Some(test_case.variation_type),
                     now,
-                )
-                .unwrap_or(None);
+                );
 
                 let result_assingment = result
                     .as_ref()

datadog-ffe/src/rules_based/mod.rs

@@ -12,7 +12,7 @@ mod ufc;
 
 pub use attributes::Attribute;
 pub use configuration::Configuration;
-pub use error::EvaluationError;
+pub use error::{EvaluationError, EvaluationFailure};
 pub use eval::{get_assignment, EvaluationContext};
 pub use str::Str;
 pub use timestamp::{now, Timestamp};