`get self(): this` in an interface crashes the checker (6.0 regression)

[tonyboho]

🔎 Search Terms

getConditionalFlowTypeOfType, getAnnotatedAccessorType, Cannot read properties of undefined (reading 'flags'), accessor this type

🕗 Version & Regression Information

• Crashes in 6.0.3 and nightly (6.0.0-dev.20260416); 5.9.3 is clean — a 6.0 regression

💻 Code

interface I {
    get self(): this
}

🙁 Actual behavior

tsc crashes:

TypeError: Cannot read properties of undefined (reading 'flags')
    at getConditionalFlowTypeOfType (typescript/lib/_tsc.js:65892:23)
    at getTypeFromTypeNode (typescript/lib/_tsc.js:68622:12)
    at getAnnotatedAccessorType (typescript/lib/_tsc.js:62162:20)
    at getTypeOfAccessors (typescript/lib/_tsc.js:62180:99)
    at checkAccessorDeclarationDiagnostics (typescript/lib/_tsc.js:87089:26)

Any this nested inside the accessor's return type annotation triggers it too (get pair(): [this, string]). A method or property signature with the same this type is fine.

🙂 Expected behavior

No crash (5.9 checks this without errors).

Additional information about the issue

No response

[RyanCavanaugh]

Doesn't repro in 7.0; marking as Fixed.

I don't think this meets the bar for a 6.0 patch - readonly self: this; is an OK workaround since it seems extremely unlikely you would have a setter in this case.

[tonyboho]

Shouldn't it be pinned with a test, to avoid regressions in the future?

[RyanCavanaugh]

Feel free to send a PR with a test, no objections to that