When callling graphql-core's execute() function with variable_values which do not pass validation -- for example, including an unexpected key in the variable_values dictionary -- the current behavior is that an ExecutionResult object is returned from the function, with the associated GraphQLError present inside it. Instead, this should be treated as a Request error, according to the spec, meaning that a GraphQLError should be raised from execute().

The GraphQL spec states:

Request errors
Request errors are raised before execution begins. This may occur due to a parse grammar or validation error in the requested document, an inability to determine which operation to execute, or invalid input values for variables.

This means that it is incorrect for the coerce_variable_values function to be returning a GraphQLError inside an ExecutionResult:

doing so means that a response payload is returned containing both an "errors" key and a null "data" key. Again, this a violation of the spec:

If a request error is raised, execution does not begin and the data entry in the response must not be present. The errors entry must include the error.