Missing error about inability to access conflicting private properties on generic types involving intersections

🔎 Search Terms

accessibility private intersection never reduced conflicting

🕗 Version & Regression Information

• This changed in PR: https://github.com/microsoft/TypeScript/pull/37762 - the error was present before this PR, there was a test for it: https://github.com/microsoft/TypeScript/pull/37762/files#diff-ca0ed2db9207146d34393eb3428bf91872b53a7d882b1e010312ec6f02b9d08aL24

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=6.0.0-dev.20250817#code/MYGwhgzhAECC0G8BQ1oAcBOBLAbmALgKbRgBci0AZgPbXkB2ArgLYBGhG0AvgNxJdIkoSDABCiFOmx4iJcgmiswGchHzZ6Ac258BSfAE80xABoAeACrRCADyL0AJjFgA+aAF5oAbQteARGB+ALoANNAAFFYAPtCiAJT+gUFBPNAA9GnWGBjUGBCChsbQAJqW1naEjs7QMaJunr4BwakZWTkYBUbEAFpltvZOcNAAZLH10I1JLZn01G25APydRd0A+n0VVUOjdR4TicH+rId+wCcOzemZILQA1mEA7sTAYPTWOJXQmnPAGGAAXgYSI4SMBgIQoNAHIRCGhoIx6LdZg83phqMYMPgsBDlj0AIwbAbOcaTS6tDjtXHQboAJkJlUGuwaBxSV3mHX0XWpAGZ6VtYGELDTykSxntIiMJjSEk1Wa1ZuylpyVtz1lZ+gznILhRqtkyIlZRkKZUkjiczkF-Bc5dc7o9nq93p9vtBfgCga8HKDwZDobD4YjkaichisTigA

💻 Code

class A {
  private a: { foo: number };
}

class B {
  private a: { bar: string };
}

type X<T extends A> = [T["a"], (T | B)["a"]]; // errors

type Y<T extends A | B> = T["a"]; // error

type Z<T extends A & B> = T["a"]; // no error?

type Z_<T extends A & B> = T["a"]["b"]["c"]["d"]; // look, we can even go crazy and access deep unknown properties

type Z1<T extends A> = T["a"]; // error

type Z2<T extends B> = T["a"]; // error

type Z3<T extends A, T2 extends B> = (T & T2)["a"]; // no error?

type Z3_<T extends A, T2 extends B> = (T & T2)["a"]["b"]["c"]["d"]; // look, we can even go crazy and access deep unknown properties

🙁 Actual behavior

Z, Z_, Z3 and Z3_ have no errors

🙂 Expected behavior

I would expect the above type aliases to all contain errors

Additional information about the issue

somewhat related to https://github.com/microsoft/TypeScript/issues/62178

Beginne mit der bereitgestellten TypeScript Playground-Reproduktion und vergleiche die Aliase mit Beteiligung von Schnittmengen, privaten Eigenschaften und tiefen indizierten Zugriffen mit den Fällen, die bereits Fehler melden. Verfolge das Verhalten der Typprüfung rund um diese generischen Constraints und prüfe den zugehörigen Issue sowie den Regression-PR; fertig ist es, wenn Z, Z_, Z3 und Z3_ die erwarteten Zugriffsfehler erzeugen.