[Timur Vural (timurzvural)]

Fixes #65069.

Bug

In 7.1, a destructured parameter with a default like = [] loses its contextual type and reports TS7031 on binding elements. The object form (= {}) is #64974; this PR covers the array form and also guards object padding the same way.

type F = (input?: [string?, number?]) => number;
export const f: F = ([a, b] = []) => (a ? 1 : 0) + (b ?? 0);

Fix

In checkDeclarationInitializer, only call padTupleType / padObjectLiteralType when getContextualTypeForVariableLikeDeclaration(root, ContextFlagsNone) == nil. Padding invents any-typed missing elements and must not override a contextual parameter type.

Tests

Extended objectBindingPatternDefaultMissingElements.ts (and baselines) with array/= [] cases from #65069 and an object/= {} case.

Related

• Fixes 7.1: array-destructured parameter with a = [] default loses its contextual type (TS7031) #65069
• Also covers the object side of 7.1: destructured parameter with a = {} default loses its contextual type (TS7031) #64974 (open fix(64974): fix contextual typing for destructured parameter defaults #64978 only guards objects today)
• Overlaps with fix(65011): preserve contextual types for destructured parameter defaults #65016

AI assistance disclosure

This PR was authored with assistance from Cursor Agent. I have read and understand the change and am prepared to discuss and revise it in review.

[Copilot]

🟢 Approval recommended

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What changed in this PR

Fixes #65069 by preserving contextual types for array-destructured parameter defaults in the native TypeScript checker. The same guard also addresses object defaults from #64974.

Changes:

• Skip tuple and object padding when the parameter has a contextual type.
• Add regression cases for object defaults, array defaults, callbacks, and nested/rest destructuring.
• Update type, symbol, and diagnostic baselines.

File	Description
tsc/​testdata/​tests/​cases/​compiler/​objectBindingPatternDefaultMissingElements.ts	Adds contextual-typing regression cases.
tsc/​testdata/​baselines/​reference/​compiler/​objectBindingPatternDefaultMissingElements.types	Records preserved binding-element types.
tsc/​testdata/​baselines/​reference/​compiler/​objectBindingPatternDefaultMissingElements.symbols	Records symbols for the added cases.
tsc/​testdata/​baselines/​reference/​compiler/​objectBindingPatternDefaultMissingElements.errors.txt	Records expected assignment errors that verify contextual typing.
tsc/​internal/​checker/​checker.go	Guards object and tuple padding with a contextual-type check.

_{Review effort: Balanced}