typescript-tuple-rest-spread-bug

Compile error bug related to spreading tuple types for rest parameters

This bug is related to the features described in this (merged) pull request: microsoft/TypeScript#24897

Description

This issue was discovered when implementing a type-safe event emitter class.

• index.ts defines an unimplemented EventEmitter that includes 4 functions which should be equivalent (except for the eventName parameter).
• test.ts consumes the EventEmitter class and calls the various functions to test type-safety.

An Events interface is used to define the supported events by mapping the event name to a tuple type for the parameters of the event listener. This interface is passed through a generic parameter E in the Test class and then passed through a generic parameter E in the EventEmitter class.

The unexpected behavior occurs on lines 29 and 33 (in test.ts). Despite the events producing two boolean values, a listener function should be able to define 1 parameter and only have access to the first parameter passed.

The unexpected behavior only occurs when the Events interface type has to pass through 2 generic class parameters. If line 14 is uncommented, and line 13 is commented then all unexpected behavior is resolved.