Switch aggregate to iterating directly within Is and As

trace.go

@@ -454,35 +454,26 @@ func (r aggregate) Error() string {
 	return output
 }
 
-// Unwrap implements `errors.Unwrap` in a somewhat unusual way to support
-// `errors.Is` and `errors.As`.
-//
-// One might expect Unwrap to return the error at the head of the slice, but,
-// instead we return the slice excluding the head. This, in combination with
-// `aggregate.Is` re-invoking `errors.Is` on the head of the slice essentially
-// allows for the original `errors.Is` to navigate the tree of error chains
-// created by `aggregate`.
-//
-// Reading the implementation for `errors.Is` and `errors.As` should provide
-// some further explanation.
-func (r aggregate) Unwrap() error {
-	if len(r) == 1 {
-		return nil
-	}
-
-	return r[1:]
-}
-
-// Is implements the errors.Is interface by re-invoking errors.Is on the error
-// at the head of the slice.
+// Is implements the `Is` interface, by iterating through each error in the
+// aggregate and invoking `errors.Is`.
 func (r aggregate) Is(t error) bool {
-	return errors.Is(r[0], t)
+	for _, err := range r {
+		if errors.Is(err, t) {
+			return true
+		}
+	}
+	return false
 }
 
-// As implements the errors.As interface by re-invoking errors.As on the error
-// at the head of the slice.
+// As implements the `As` interface, by iterating through each error in the
+// aggregate and invoking `errors.As`.
 func (r aggregate) As(t interface{}) bool {
-	return errors.As(r[0], t)
+	for _, err := range r {
+		if errors.As(err, t) {
+			return true
+		}
+	}
+	return false
 }
 
 // Errors obtains the list of errors this aggregate combines