Expose More Information About Expression Parsing Errors

core/player/src/expressions/parser.ts

@@ -2,7 +2,12 @@
 /**
  * An expression to AST parser based on JSEP: http://jsep.from.so/
  */
-import type { ExpressionNode, ExpressionNodeType, NodeLocation } from './types';
+import type {
+  ErrorWithLocation,
+  ExpressionNode,
+  ExpressionNodeType,
+  NodeLocation,
+} from './types';
 import { ExpNodeOpaqueIdentifier } from './types';
 
 const PERIOD_CODE = 46; // '.'
@@ -62,16 +67,8 @@ const binaryOps: Record<string, number> = {
   '%': 14,
 };
 
-interface ErrorWithLocation extends Error {
-  /** The place in the string where the error occurs */
-  index: number;
-
-  /** a helpful description */
-  description: string;
-}
-
 /** Wrap the message and index in an error and throw it */
-function throwError(message: string, index: number) {
+function throwError(message: string, index: number): ErrorWithLocation {
   const err = new Error(`${message} at character ${index}`);
 
   (err as ErrorWithLocation).index = index;

core/player/src/expressions/types.ts

@@ -231,3 +231,11 @@ export type ExpressionNode =
   | ObjectNode;
 
 export type ExpressionNodeType = ExpressionNode['type'];
+
+export interface ErrorWithLocation extends Error {
+  /** The place in the string where the error occurs */
+  index: number;
+
+  /** a helpful description */
+  description: string;
+}

core/player/src/expressions/utils.ts

@@ -1,5 +1,6 @@
 import { isExpressionNode } from './types';
 import type {
+  ErrorWithLocation,
   ExpressionHandler,
   ExpressionNode,
   ExpressionObjectType,
@@ -148,3 +149,13 @@
     'value' in expr
   );
 }
+
+/**
+ * Type guard for ErrorWithLocation
+ */
+export function isErrorWithLocation(error: Error): error is ErrorWithLocation {
+  return (
+    (error as ErrorWithLocation).index !== undefined &&
+    (error as ErrorWithLocation).description !== undefined
+  );
+}