test(types): restore TypeScript 5.9 to CI matrix#2464
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TS 5.9 tightened conditional-return-type assignability, which surfaced five errors in two helper modules where generic returns relied on flow narrowing through user-defined type guards. TypeScript does not propagate value-side narrowing back into a generic conditional return type, so each site needed either overloads or a typed cast. - callProp: replaced the conditional return with function overloads so no cast is required in the body. - computeGoal: rewrote as guarded returns, each branch cast to T. - getDefaultProp: return type widened to T[P] | undefined to match actual behaviour; existing callers already handled undefined. - toArray: replaced as-any with as-Arrify on the result. Restored 5.9 to the test-types matrix. Verified clean on tsc --noEmit against 5.0, 5.4, 5.7, 5.9. Closes #2441
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Summary
TypeScript 5.9 tightened conditional-return-type assignability, which broke five generic helpers in the core/shared packages. Each return type was correct in intent but unprovable to the compiler because TS does not propagate value-side narrowing through user-defined type guards back into a generic conditional return type. Patched each site with the most honest option available and restored 5.9 to the
test-typesmatrix.Approach
Per site, picked the cleanest fix:
callProp— replaced the single conditional-return signature with function overloads so no cast is needed in the body.computeGoal— rewrote as guarded returns, each branch cast to the declared return typeT.getDefaultProp— widened the return type toT[P] | undefinedto match actual behaviour. Existing callers (SpringValue,Controller,hasDefaultProp) already handle undefined viais.und,=== true, or!==.toArray— replacedas anywithas Arrify<Exclude<T, void>>on the result.as anywas deliberately avoided —as <ReturnType>keeps the structural compatibility check the compiler can still perform.Verification
tsc --noEmitclean on TS 5.0, 5.4, 5.7, 5.9. Unit suite passes (217 tests).Closes #2441