microsoft
Fix compiler crash on generics overload resolution failure
Fixes #61524
Replace Debug.fail() calls with proper error generation to prevent TypeScript compiler crashes when overload resolution fails for complex generic constraints, for example JSX elements.
Problem
The TypeScript compiler crashes with "Debug Failure. No error for last overload signature" when resolving certain complex generic constraints, e.g., JSX element types. This regression has existed since TypeScript 3.6 and affects many React/JSX projects.
Root Cause
When getSignatureApplicabilityError() returns no diagnostics for overload candidates, the compiler calls Debug.fail() instead of handling the edge case gracefully, causing an immediate crash.
Solution
- Replace
Debug.fail()calls with fallback diagnostic generation - Generate appropriate error messages for unhandled overload resolution cases
- Ensure compiler continues execution without crashing
Note
This change doesn’t fix the core logic of type inference. Ideally, that core should be fixed, but this pull request only addresses the compiler crash.
Related to #61524, #60229, #48636, #33133
I think this is just papering over a bug somewhere else. IIRC the intent of these debug fails are to assert that the previous steps added an error.
@jakebailey Thank you for your comment. Are you saying that the core issue lies in type inference, or somewhere else? It makes sense from a language-processor perspective, but in our project the crash occurs during type checking, and it has been blocking us from upgrading from v5.6.3; this suggests the problem first appeared in v5.7.
If it's a regression, I would consider bisecting with https://www.npmjs.com/package/every-ts
I don't think this is a regression. It appears that the problem still occurs on the latest main branch.
But you said it wasn't broken in 5.5, so there is a commit in between where this broke.
But, https://github.com/microsoft/TypeScript/issues/61524#issuecomment-2780342066 seems to imply there's already a PR for this?