[Timur Vural (timurzvural)]

Bug

In 7.1, a destructured parameter with a default like = {} (or = []) loses its contextual type and reports TS7031 on binding elements. This worked in 5.9 and 7.0.

Example (also fails for the same shape in .ts):

/** @returns {Adapter} */
export function make() {
  return {
    async structure(c, { signal } = {}) {
      signal?.throwIfAborted()
      return [c]
    },
  }
}

Root cause

checkDeclarationInitializer always called padObjectLiteralType / padTupleType for parameter binding patterns. Padding invents any-typed missing properties and overrides the contextual parameter type.

Fix

Only pad when getContextualTypeForVariableLikeDeclaration(root, ContextFlagsNone) == nil, for both object and array binding patterns.

Tests

• Extended objectBindingPatternDefaultMissingElements.ts (+ baselines) with cases from 7.1: destructured parameter with a = {} default loses its contextual type (TS7031) #64974 / Regression in 7.1: contextual parameter type is lost for a destructuring pattern with a default (TS7031) #65011
• New contextualDestructuredParameterDefault.ts (+ symbols/types baselines) covering the JSDoc @returns method, cast, and .ts annotation shapes from Regression in 7.1: contextual parameter type is lost for a destructuring pattern with a default (TS7031) #65011

Related

• Fixes Regression in 7.1: contextual parameter type is lost for a destructuring pattern with a default (TS7031) #65011
• Also covers 7.1: destructured parameter with a = {} default loses its contextual type (TS7031) #64974
• Similar to open fix(64974): fix contextual typing for destructured parameter defaults #64978; this alternative also guards array padding and adds the Regression in 7.1: contextual parameter type is lost for a destructuring pattern with a default (TS7031) #65011 JSDoc / contextual cases

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

No active review issues block approval of the contextual-typing regression fix.

No open issues 🎉

What changed in this PR

Fixes the TypeScript 7.1 regression in #65011 and #64974 where destructured parameter defaults lose contextual types and incorrectly report TS7031.

Changes:

• Skips object and tuple padding when the parameter already has a contextual type.
• Adds regression cases and baselines covering TypeScript callbacks, nested destructuring, array patterns, and JSDoc contextual typing.

File	Description
tsc/​testdata/​tests/​cases/​compiler/​objectBindingPatternDefaultMissingElements.ts	Expands contextual typing and destructuring coverage.
tsc/​testdata/​tests/​cases/​compiler/​contextualDestructuredParameterDefault.ts	Adds JSDoc and TypeScript cases from #65011.
tsc/​testdata/​baselines/​reference/​compiler/​objectBindingPatternDefaultMissingElements.types	Records inferred types for expanded cases.
tsc/​testdata/​baselines/​reference/​compiler/​objectBindingPatternDefaultMissingElements.symbols	Records symbol bindings for expanded cases.
tsc/​testdata/​baselines/​reference/​compiler/​objectBindingPatternDefaultMissingElements.errors.txt	Records expected diagnostics for negative cases.
tsc/​testdata/​baselines/​reference/​compiler/​contextualDestructuredParameterDefault.types	Records preserved contextual parameter types.
tsc/​testdata/​baselines/​reference/​compiler/​contextualDestructuredParameterDefault.symbols	Records symbols for the new regression cases.
tsc/​internal/​checker/​checker.go	Guards parameter initializer padding against overriding contextual types.

_{Review effort: Balanced}