7.1: destructured parameter with a = {} default loses its contextual type (TS7031) #64974

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1. jltrv commented on Oct 27, 2026

   

   Jacques Latrive (jltrv)

   on Oct 27, 2026

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   Two more variants of the same regression, both fine on 7.0.2 and both still failing on 7.1.0-dev.20261027.1.

   1. Explicitly annotated parameter, no contextual typing. A pattern nested under a property with a = {} default loses the declared type:

   type Options = { inner?: { x?: string; y?: string } };
   
   export function f({ inner: { x, y } = {} }: Options) {
     return `${x}${y}`;
   }
   
   // Top-level pattern with an annotation and a `= {}` default: no error on any version
   export function g({ x, y }: { x?: string; y?: string } = {}) {
     return `${x}${y}`;
   }

   2. Non-empty object literal default. Only the properties missing from the initializer are flagged:

   type Props = { a: boolean; b?: string };
   type Fn = (props: Props) => string;
   
   export const h: Fn = ({ a, b } = { a: false }) => `${a}${b}`;

   tsconfig.json: { "compilerOptions": { "strict": true, "target": "es2022", "module": "nodenext", "noEmit": true } }

   Version	Result
   6.0.2, 7.0.2	no errors
   7.1.0-beta, 7.1.0-dev.20261027.1	error TS7031: Binding element 'x' implicitly has an 'any' type. and the same for y (1), and for b (2)

   So it looks like 7.1 types a binding element missing from an object-literal initializer as implicit any instead of taking the type from the declared or contextual parameter type. An annotation on the parameter itself (g) is still honoured.

   For scale: in our codebase this accounts for all 65 new errors between 7.0.2 and 7.1.0-beta, across 23 files. They're a mix of these two forms, the contextually typed callbacks from the original report, and array.map(({ a, b } = {}) => …) callbacks.