execution: Preserve extensions in parseValue errors

Previously, the only fields observed on an error thrown by (for example)
parseValue were `message` and `originalError`. Now, if an error has no
`originalError`, it is itself used as the original error.

Addresses an issue raised in
apollographql/apollo-server#7178

src/execution/__tests__/variables-test.ts

@@ -5,6 +5,8 @@ import { expectJSON } from '../../__testUtils__/expectJSON.js';
 
 import { inspect } from '../../jsutils/inspect.js';
 
+import { GraphQLError } from '../../error/GraphQLError.js';
+
 import { Kind } from '../../language/kinds.js';
 import { parse } from '../../language/parser.js';
 
@@ -29,6 +31,11 @@ import { getVariableValues } from '../values.js';
 const TestComplexScalar = new GraphQLScalarType({
   name: 'ComplexScalar',
   parseValue(value) {
+    if (value === 'ThrowAnError') {
+      throw new GraphQLError('parseValue throws', {
+        extensions: { custom: 'extension' },
+      });
+    }
     expect(value).to.equal('SerializedValue');
     return 'DeserializedValue';
   },
@@ -366,6 +373,22 @@ describe('Execute: Handles inputs', () => {
         });
       });
 
+      it('propagates GraphQLError from parseValue', () => {
+        const params = { input: { c: 'foo', d: 'ThrowAnError' } };
+        const result = executeQuery(doc, params);
+
+        expectJSON(result).toDeepEqual({
+          errors: [
+            {
+              message:
+                'Variable "$input" got invalid value "ThrowAnError" at "input.d"; parseValue throws',
+              locations: [{ column: 16, line: 2 }],
+              extensions: { custom: 'extension' },
+            },
+          ],
+        });
+      });
+
       it('errors on null for nested non-null', () => {
         const params = { input: { a: 'foo', b: 'bar', c: null } };
         const result = executeQuery(doc, params);

src/execution/values.ts

@@ -131,7 +131,7 @@ function coerceVariableValues(
         onError(
           new GraphQLError(prefix + '; ' + error.message, {
             nodes: varDefNode,
-            originalError: error.originalError,
+            originalError: error.originalError ?? error,
           }),
         );
       },