No check for access modifier for non-trivial class properties

[danielrentz]

TypeScript Version: 3.7.2

Search Terms: private computed property

Expected behavior:

TypeScript should check the access modifier of class properties with "weird" names that look like computed properties but are given literally (e.g. property names with dashes).

I understand that there is an intended bypass for "real" computed properties where the index is a non-constant expression (https://github.com/Microsoft/TypeScript/blob/master/doc/spec.md#413-property-access). But properties explicitly defined in the class should be checked when accessed literally (see playground example).

Actually, TypeScript even acts a little inconsistent: It fails if trying to access a class property that does not exist, but passes accessing private properties from outside.

Actual behavior:

TypeScript fails for undefined properties, but not for existing private properties.

Related Issues: #26328

Code

class C {
    public p1 = 1;
    private p2 = 1;
    public ["p-1"] = 1;
    private ["p-2"] = 1;
}

const c = new C;
console.log(c.p0); // error (ok)
console.log(c.p1);
console.log(c.p2); // error (ok)
console.log(c["p-0"]); // error (ok)
console.log(c["p-1"]);
console.log(c["p-2"]); // no error!

Compiler Options

{
  "compilerOptions": {
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "strictPropertyInitialization": true,
    "strictBindCallApply": true,
    "noImplicitThis": true,
    "noImplicitReturns": true,
    "useDefineForClassFields": false,
    "alwaysStrict": true,
    "allowUnreachableCode": false,
    "allowUnusedLabels": false,
    "downlevelIteration": false,
    "noEmitHelpers": false,
    "noLib": false,
    "noStrictGenericChecks": false,
    "noUnusedLocals": false,
    "noUnusedParameters": false,
    "esModuleInterop": true,
    "preserveConstEnums": false,
    "removeComments": false,
    "skipLibCheck": false,
    "checkJs": false,
    "allowJs": false,
    "declaration": true,
    "experimentalDecorators": false,
    "emitDecoratorMetadata": false,
    "target": "ES2017",
    "module": "ESNext"
  }
}

Playground Link: Provided

[ajafff]

How is this different from #26328?

[danielrentz]

From #26328: const n = a[nameN]; with nameN being a variable (well in real-life). This issue is specifically about object["literal"]. And ... about undefined vs. private properties behaving differently.

[RyanCavanaugh]

This is longstanding behavior to allow (ugh) the access of these properties. It'd be a very substantial breaking change at this point and we don't intend to invoke that pain.