Sandbox::https://github.com/microsoft/TypeScript/pull/64671

dev (Konan69) · 2026-10-07T15:51:09Z

#64043 made padObjectLiteralType pad every binding element missing from a parameter's default object literal, using the element's own type, which is implicitly any when the element has no initializer. For an annotated or contextually typed parameter this reports TS7031 on an element that already has a type, and for nested patterns it also replaces that type with any:

type Options = (options?: { recursive?: boolean }) => void;
export const f: Options = ({ recursive } = {}) => {
    const proof: string = recursive; // TS2322: boolean | undefined is not assignable to string
};
// and on the line above: TS7031 Binding element 'recursive' implicitly has an 'any' type.

interface Outer { inner?: { b?: number } }
export function g({ inner: { b } = {} }: Outer) {} // TS7031 on 'b'

Change

padObjectLiteralType now resolves the type the pattern destructures from the parameter's annotation or its contextual signature, walking nested object patterns by property name, and does not pad an element that this type has. Elements the type does not have are padded and reported exactly as before, so a parameter with no type anywhere keeps its TS7031, which is what #64043 intended. The lookup (getDeclaredTypeOfParameterBindingPattern) never consults an initializer.

The first version of this PR only suppressed the diagnostic. The review pointed out that a nested contextually typed element then stayed any silently; that was right, and this version fixes the type as well as the diagnostic.

Relation to #64440

I saw the draft in #64440 after starting this. It skips the padding only when every element of the pattern resolves through the contextual type. This PR decides per element, which differs in one case I could find:

export const partial: (options?: { known?: number }) => void = ({ known, unknown } = {}) => {};

	`known`	`unknown`
7.0.2	no error	TS2339
#64440 (built locally)	TS7031, although its type is `number \| undefined`	TS2339, TS7031
this PR	no error	TS2339, TS7031

On every other case below the two give the same result. Please close this if you prefer to finish #64440.

Tests

Added to objectBindingPatternDefaultMissingElements, each with an assignment to string so the errors baseline shows the element's type:

contextually typed by a function type, by a callback argument, by an interface method;
a nested pattern under a contextual type;
the partial case above;
the two annotated nested forms from TS7031 false positive for nested object binding pattern with = {} default in an annotated parameter (regression from #64043) #64431.

go test ./internal/testrunner -run TestLocal and go test ./internal/checker/... pass; the only baselines that change are that test's, and its 5 intended TS7031 errors are unchanged. I have not run hereby lint or the submodule tests.

How we found it

We were evaluating type checkers and build tooling for a large TypeScript monorepo (an AI product: 17 projects, Effect 4). A checker that tracks current main reported 3 lines that 7.0.2 does not, all this error, on an object literal implementing an SDK interface (mkdir: (path, { recursive } = {}) => ...). Bisecting the nightlies gave 7.1.0-dev.20260922.1 as the last good and 7.1.0-dev.20260923.1 as the first bad; 6.0.3 and 7.0.2 accept the code.

For reference, the whole-repo check on that monorepo, cold, 17 projects with declarations, on a 16-core machine:

	Time	Peak memory (largest process)
`tsc` 7.0.2, `--checkers 1`	28.3 s	1.97 GB
`tsc` 7.0.2, default checkers	19.1 s	3.08 GB

AI disclosure

This patch was written with an AI coding tool. I have read it, I understand it, and I will handle the review myself.

Copilot

🟡 Changes recommended

Nested contextual bindings can remain implicitly any while their diagnostic is suppressed.

1 open finding

Avoid suppressing TS7031 when nested context does not provide a type · New

What changed in this PR

Prevents false TS7031 diagnostics for typed binding elements with default object literals.

Changes:

Gates implicit-any reporting on root parameter typing.
Adds contextual and annotated regression cases with baselines.

File	Description
`tsc/internal/checker/checker.go`	Adjusts implicit-any reporting.
`tsc/testdata/tests/cases/compiler/objectBindingPatternDefaultMissingElements.ts`	Adds regression cases.
`tsc/testdata/baselines/reference/compiler/objectBindingPatternDefaultMissingElements.types`	Updates type baseline.
`tsc/testdata/baselines/reference/compiler/objectBindingPatternDefaultMissingElements.symbols`	Updates symbol baseline.
`tsc/testdata/baselines/reference/compiler/objectBindingPatternDefaultMissingElements.errors.txt`	Updates diagnostic baseline.

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dev (Konan69) · 2026-10-07T16:46:38Z

+	// gets its binding element types from the annotation and a contextually typed one from the
+	// contextual signature, so the implicit any error would contradict the element's own type.
+	root := ast.GetRootDeclaration(pattern.Parent)
+	reportErrors := !(ast.IsParameterDeclaration(root) && (root.Type() != nil || c.getContextuallyTypedParameterType(root) != nil))


Good catch, that was right. The new commit resolves each element through the annotation or contextual type and skips the padding for it, so the nested case is boolean | undefined again, and the test now asserts the types.

padObjectLiteralType pads every binding element missing from a parameter's default object literal with the element's own type, which is implicitly any when the element has no initializer. For an annotated or contextually typed parameter that replaces the type the annotation or the contextual signature gives the element, and reports TS7031 on an element that has a type: type Options = (options?: { recursive?: boolean }) => void; const f: Options = ({ recursive } = {}) => {}; // ~~~~~~~~~ TS7031, but recursive is boolean | undefined Resolve the type the pattern destructures from the annotation or the contextual signature, through nested patterns, and leave out of the padding each element that type has. Elements it does not have are padded and reported as before.

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Copilot AI balanced review requested due to automatic review settings October 7, 2026 15:51

typescript-automation Bot assigned Ryan Cavanaugh (RyanCavanaugh) Oct 7, 2026

typescript-automation Bot added the For Uncommitted Bug PR for untriaged, rejected, closed or missing bug label Oct 7, 2026

dev (Konan69) mentioned this pull request Oct 7, 2026

TS7031 false positive for nested object binding pattern with = {} default in an annotated parameter (regression from #64043) #64431

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Copilot started reviewing on behalf of dev (Konan69) October 7, 2026 15:52 View session

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dev (Konan69) force-pushed the fix/contextual-binding-default-implicit-any branch from c435387 to 42826db Compare October 7, 2026 16:23

dev (Konan69) changed the title ~~Do not report implicit any for typed binding elements missing from a default~~ Do not pad binding elements that the parameter's type already types Oct 7, 2026

dev (Konan69) mentioned this pull request Oct 7, 2026

checker: do not pad binding elements that the parameter's type already types pingdotgg/ts-rust#17

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Theo Browne (t3dotgg) mentioned this pull request Oct 7, 2026

TS7031 on a contextually typed parameter with a destructured = {} default pingdotgg/ts-rust#16

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Do not pad binding elements that the parameter's type already types - #64671

Do not pad binding elements that the parameter's type already types#64671
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Relation to #64440

Tests

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dev (Konan69) commented Oct 7, 2026 •

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