False positive assignment error with generics when using --strictBindCallApply

[ulrichb]

TypeScript Version: 3.3.0-dev.20181207

Search Terms: bind generic strict

Code

class SomeClass {

    constructor() {
        this.genericMethod = this.genericMethod.bind(this);
        
        // TS2322: Type '(callback: (p: {}) => {}) => void' is not
        // assignable to type '<T>(callback: (p: T) => T) => void':
        this.genericWithCallback = this.genericWithCallback.bind(this);
    }

    genericMethod<T>(p: T): void { }

    genericWithCallback<T>(callback: (p: T) => T): void { }
}

Compile with tsc TypeScriptIssue.ts --target es6 --strictBindCallApply

Expected behavior:
No compile error

Actual behavior:

error TS2322: Type '(callback: (p: {}) => {}) => void' is not assignable to type '<T>(callback: (p: T) => T) => void'.
  Types of parameters 'callback' and 'callback' are incompatible.
    Types of parameters 'p' and 'p' are incompatible.
      Type '{}' is not assignable to type 'T'.

Playground Link: (no --strictBindCallApply flag available)

Related issues:

• Strict bind, call, and apply methods on functions #27028
• [3.2.0-rc] .bind with overloads causes compile error in strict mode (strictBindCallApply) #28582

[ahejlsberg]

This is a known and unfortunate design limitation. See comment here. We're thinking about ways to alleviate the issue.

[ulrichb]

@ahejlsberg Ah, okay. Didn't find that. Thanks for the link. I'll leave this issue open for discoverability.