Bug: Accessing private statics in a class via its derived class is allowed

Description

class FooBase {
    private static privateStatic: string = "";

    testBase(): void {
        console.log(FooBase.privateStatic);

        // Should error, but doesn't
        console.log(Foo.privateStatic);
   }
}

class Foo extends FooBase {
    test() {
        // Should error, and does
        console.log(Foo.privateStatic);
    }
}

Contributor guide

Tech stack

typescript

Domain

tooling

Issue type

bug

DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.

3

Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.

1-3 hours

Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.

stale

ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.

clear

Prerequisites

Basic TypeScriptAccess modifiersTypeScript compiler building process

Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.

50

Research direction

The issue is in the TypeScript checker, specifically in how private static members are accessed from derived classes. The expected fix is to ensure that a base class cannot access a derived class's private static member. Look at the accessibility checking logic in checker.ts, around the handling of property access expressions. The bug is that when accessing Foo.privateStatic from FooBase, the checker incorrectly allows it because it considers FooBase as the declaring class for the purpose of private access. The fix should involve ensuring that the declaring class is exactly the class where the member is defined, not any base class. There are no linked PRs, but the discussion in the issue may provide additional insights.