[3.2.0-rc] .bind with overloads causes compile error in strict mode (strictBindCallApply)

[eamodio]

TypeScript Version: 3.2.0-rc

Search Terms:
strictBindCallApply, bind, overload

Code

class Logger {
 static debug(message: string, ...params: any[]): void;
 static debug(context: object | undefined, message: string, ...params: any[]): void;
 static debug(contextOrMessage: object | string | undefined, ...params: any[]): void {
 // ...
 }

 static log(message: string, ...params: any[]): void;
 static log(context: object | undefined, message: string, ...params: any[]): void;
 static log(contextOrMessage: object | string | undefined, ...params: any[]): void {
 // ...
 }
}

// @log decorator
function log(debug: boolean) {
 // ...
 const logFn = debug ? Logger.debug.bind(Logger) : Logger.log.bind(Logger);

 // ...

 // Errors with Argument of type 'string' is not assignable to parameter of type 'object | undefined'
 // NOTE: This doesn't error without the .bind() call above
 logFn("message", 1, 2, 3);
}

Expected behavior:

Not exactly sure, but not an error

Actual behavior:

Error -- see playground link

Playground Link:

http://www.typescriptlang.org/play/index.html#src=class%20Logger%20%7B%0D%0A%20%20static%20debug(message%3A%20string%2C%20...params%3A%20any%5B%5D)%3A%20void%3B%0D%0A%20%20static%20debug(context%3A%20object%20%7C%20undefined%2C%20message%3A%20string%2C%20...params%3A%20any%5B%5D)%3A%20void%3B%0D%0A%20%20static%20debug(contextOrMessage%3A%20object%20%7C%20string%20%7C%20undefined%2C%20...params%3A%20any%5B%5D)%3A%20void%20%7B%0D%0A%20%20%20%20%2F%2F%20...%0D%0A%20%20%7D%0D%0A%0D%0A%20%20static%20log(message%3A%20string%2C%20...params%3A%20any%5B%5D)%3A%20void%3B%0D%0A%20%20static%20log(context%3A%20object%20%7C%20undefined%2C%20message%3A%20string%2C%20...params%3A%20any%5B%5D)%3A%20void%3B%0D%0A%20%20static%20log(contextOrMessage%3A%20object%20%7C%20string%20%7C%20undefined%2C%20...params%3A%20any%5B%5D)%3A%20void%20%7B%0D%0A%20%20%20%20%2F%2F%20...%0D%0A%20%20%7D%0D%0A%7D%0D%0A%0D%0A%2F%2F%20%40log%20decorator%0D%0Afunction%20log(debug%3A%20boolean)%20%7B%0D%0A%20%20%2F%2F%20...%0D%0A%20%20const%20logFn%20%3D%20debug%20%3F%20Logger.debug.bind(Logger)%20%3A%20Logger.log.bind(Logger)%3B%0D%0A%0D%0A%20%20%2F%2F%20...%0D%0A%0D%0A%20%20%2F%2F%20Errors%20with%20Argument%20of%20type%20'string'%20is%20not%20assignable%20to%20parameter%20of%20type%20'object%20%7C%20undefined'%0D%0A%20%20%2F%2F%20NOTE%3A%20This%20doesn't%20error%20without%20the%20.bind()%20call%20above%0D%0A%20%20logFn(%22message%22%2C%201%2C%202%2C%203)%3B%0D%0A%7D

Related Issues:
#28567

[ahejlsberg]

This is a known (and somewhat unfortunate) limitation of --strictBindCallApply. The stricter checking looses fidelity on generic or overloaded functions. See comment here. Specifically, for overloaded functions we always pick the last overload.

Daniel Rosenwasser (@DanielRosenwasser) Reminder that we should document these limitations in the blog post for the final release.

[ahejlsberg]

Eric Amodio (@eamodio) In terms of workarounds for this issue, you can (a) turn off --strictBindCallApply, (b) swap the overloads, or (c) use a type assertion:

const logFn = (debug ? Logger.debug.bind(Logger) : Logger.log.bind(Logger)) as typeof Logger.log;

[eamodio]

Anders Hejlsberg (@ahejlsberg) Thanks for the reply! I opted for the type assertion and to be the safest I used the following to catch if one of the methods changes signature out of sync with the other.

const logFn = (debug ? Logger.debug.bind(Logger) : Logger.log.bind(Logger)) as (typeof Logger.debug | typeof Logger.log);