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Fix crash in declaration emit with nested binding patterns#63154

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DanielRosenwasser merged 3 commits intomainfrom
copilot/fix-nested-binding-pattern-crash
Feb 18, 2026
Merged

Fix crash in declaration emit with nested binding patterns#63154
DanielRosenwasser merged 3 commits intomainfrom
copilot/fix-nested-binding-pattern-crash

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Copilot AI commented Feb 17, 2026 •
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Fixes crash when emitting declarations for parameter properties with nested binding patterns:

// @declaration: true
export class C {
  constructor(public [[x]]: any[]) {}  // Previously crashed, now emits correctly
}

Root cause: walkBindingPattern recursively processed nested patterns but continued execution, attempting to use the binding pattern as an Identifier, causing Cannot read properties of undefined (reading 'id').

Fix: Add continue after recursive call to skip identifier handling for nested patterns.

Changes:

  • src/compiler/transformers/declarations.ts: Add continue statement in walkBindingPattern when encountering nested binding patterns
  • tests/cases/compiler/declarationEmitNestedBindingPattern.ts: Add test coverage for various nested binding pattern scenarios (array, object, mixed, multiple levels)
Original prompt

This section details on the original issue you should resolve

<issue_title>Crash for declaration emit with nested binding pattern</issue_title>
<issue_description>```ts
// @declaration: true

export class C {
constructor(public [[x]]: any[]) {}
}

TypeError: Cannot read properties of undefined (reading 'id')
at getSymbolId (D:\TypeScript\node_modules\typescript\lib_tsc.js:45937:15)
at Object.serializeTypeOfDeclaration (D:\TypeScript\node_modules\typescript\lib_tsc.js:50200:82)
at inferTypeOfDeclaration (D:\TypeScript\node_modules\typescript\lib_tsc.js:131867:21)
at Object.serializeTypeOfDeclaration (D:\TypeScript\node_modules\typescript\lib_tsc.js:131677:16)
at D:\TypeScript\node_modules\typescript\lib_tsc.js:50332:213
at withContext (D:\TypeScript\node_modules\typescript\lib_tsc.js:50427:29)
at Object.serializeTypeForDeclaration (D:\TypeScript\node_modules\typescript\lib_tsc.js:50332:114)
at Object.createTypeOfDeclaration (D:\TypeScript\node_modules\typescript\lib_tsc.js:86719:24)
at ensureType (D:\TypeScript\node_modules\typescript\lib_tsc.js:112711:27)
at walkBindingPattern (D:\TypeScript\node_modules\typescript\lib_tsc.js:113594:19)


## Comments on the Issue (you are @copilot in this section)

<comments>
<comment_new><author>@DanielRosenwasser</author><body>
Basically we just need to adjust `walkBindingPattern` to continue when it hits a binding pattern. Would be good to get some more tests with different types of binding patterns at different levels.</body></comment_new>
</comments>

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@typescript-bot typescript-bot added the For Uncommitted Bug PR for untriaged, rejected, closed or missing bug label Feb 17, 2026
Copilot AI and others added 2 commits February 17, 2026 22:50
@DanielRosenwasser
Fix crash for declaration emit with nested binding pattern
5d03b8c 
- Added continue statement when walking nested binding patterns
- Added comprehensive test cases covering various nested binding patterns

Co-authored-by: DanielRosenwasser <972891+DanielRosenwasser@users.noreply.github.com>
@DanielRosenwasser
Remove unnecessary type assertion to fix lint error
4b568b5 
Co-authored-by: DanielRosenwasser <972891+DanielRosenwasser@users.noreply.github.com>
Copilot AI changed the title [WIP] Fix crash for declaration emit with nested binding pattern Fix crash in declaration emit with nested binding patterns Feb 17, 2026
@DanielRosenwasser DanielRosenwasser marked this pull request as ready for review February 18, 2026 00:20
@DanielRosenwasser DanielRosenwasser mentioned this pull request Feb 18, 2026
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Copilot AI reviewed Feb 18, 2026
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Pull request overview

Fixes a crash in the declaration emit transformer when encountering nested binding patterns inside (invalid-but-emitted) parameter properties, ensuring the emitter no longer attempts to treat a BindingPattern as an Identifier.

Changes:

  • Adjust walkBindingPattern to continue after recursively processing nested binding patterns, preventing incorrect identifier handling.
  • Add a compiler test covering nested array/object/mixed binding patterns in parameter properties and capture new baselines.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

File Description
src/compiler/transformers/declarations.ts Prevents crash in parameter-property declaration emit by skipping identifier path for nested binding patterns.
tests/cases/compiler/declarationEmitNestedBindingPattern.ts Adds regression coverage for multiple nested binding pattern shapes/levels.
tests/baselines/reference/declarationEmitNestedBindingPattern.* Baselines validating no crash and stable emit/type/symbol/error outputs.

@DanielRosenwasser DanielRosenwasser added this pull request to the merge queue Feb 18, 2026
Merged via the queue into main with commit ad04bf7 Feb 18, 2026
29 checks passed
@DanielRosenwasser DanielRosenwasser deleted the copilot/fix-nested-binding-pattern-crash branch February 18, 2026 00:45
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@jakebailey jakebailey jakebailey approved these changes

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@DanielRosenwasser DanielRosenwasser DanielRosenwasser approved these changes

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Crash for declaration emit with nested binding pattern

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