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Missing error about inability to access conflicting private properties on generic types involving intersections #62294
Description
🔎 Search Terms
accessibility private intersection never reduced conflicting
🕗 Version & Regression Information
- This changed in PR: Reduce intersections with conflicting privates, elaborate on reasons #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
💻 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 #62178
Activity
hesam-oxe commentedon May 12, 2026
I'd like to investigate this. The issue is clear —
Z,Z_,Z3,and
Z3_should all error when accessing private properties onintersection types, consistent with the other cases.
I'll look at
checker.tsaround the indexed access type resolutionand the intersection reduction logic from #37762.
/assign
hesam-oxe commentedon Jun 11, 2026
Mateusz Burzyński (@Andarist) Ryan Cavanaugh (@RyanCavanaugh) Apologies for the delay — I was deep in
LLVM X86 backend fixes and OWASP security benchmarks and this
slipped through the cracks.
I've now opened PR #63548 with the fix. The check uses the
existing
isConflictingPrivatePropertyhelper that was alreadyused in
getReducedType— just wasn't being called in the indexedaccess path.
Ready for review! 🙏