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Don't try to narrow type of a symbol within RHS of its declaration #63006

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728064d
Don't try to narrow type of a symbol within RHS of its declaration
Andarist Jan 17, 2026
ba0d77c
Get rid of `NodeCheckFlags.InCheckIdentifier`
Andarist Jan 19, 2026
878c6b2
add tests
Andarist Jan 19, 2026
c5df8c5
Merge remote-tracking branch 'origin/main' into fix/destructured-vari…
Andarist Jan 19, 2026
d14ce8a
Merge remote-tracking branch 'origin/main' into fix/destructured-vari…
Andarist Jan 24, 2026
bc2d3f6
add test
Andarist Jan 24, 2026
6695c4a
Merge remote-tracking branch 'origin/main' into fix/destructured-vari…
Andarist Feb 4, 2026
dbf025b
add test
Andarist Feb 4, 2026
a16aaf0
add test
Andarist Feb 4, 2026
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29 changes: 12 additions & 17 deletions src/compiler/checker.ts
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Expand Up @@ -30853,7 +30853,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
function getNarrowedTypeOfSymbol(symbol: Symbol, location: Identifier) {
const type = getTypeOfSymbol(symbol);
const declaration = symbol.valueDeclaration;
if (declaration) {
if (declaration && !textRangeContainsPositionInclusive(getRootDeclaration(declaration), location.pos)) {
// If we have a non-rest binding element with no initializer declared as a const variable or a const-like
// parameter (a parameter for which there are no assignments in the function body), and if the parent type
// for the destructuring is a union type, one or more of the binding elements may represent discriminant
Expand Down Expand Up @@ -30881,23 +30881,18 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
const parent = declaration.parent.parent;
const rootDeclaration = getRootDeclaration(parent);
if (rootDeclaration.kind === SyntaxKind.VariableDeclaration && getCombinedNodeFlagsCached(rootDeclaration) & NodeFlags.Constant || rootDeclaration.kind === SyntaxKind.Parameter) {
const links = getNodeLinks(parent);
if (!(links.flags & NodeCheckFlags.InCheckIdentifier)) {
links.flags |= NodeCheckFlags.InCheckIdentifier;
const parentType = getTypeForBindingElementParent(parent, CheckMode.Normal);
const parentTypeConstraint = parentType && mapType(parentType, getBaseConstraintOrType);
links.flags &= ~NodeCheckFlags.InCheckIdentifier;
if (parentTypeConstraint && parentTypeConstraint.flags & TypeFlags.Union && !(rootDeclaration.kind === SyntaxKind.Parameter && isSomeSymbolAssigned(rootDeclaration))) {
const pattern = declaration.parent;
const narrowedType = getFlowTypeOfReference(pattern, parentTypeConstraint, parentTypeConstraint, /*flowContainer*/ undefined, location.flowNode);
if (narrowedType.flags & TypeFlags.Never) {
return neverType;
}
// Destructurings are validated against the parent type elsewhere. Here we disable tuple bounds
// checks because the narrowed type may have lower arity than the full parent type. For example,
// for the declaration [x, y]: [1, 2] | [3], we may have narrowed the parent type to just [3].
return getBindingElementTypeFromParentType(declaration, narrowedType, /*noTupleBoundsCheck*/ true);
const parentType = getTypeForBindingElementParent(parent, CheckMode.Normal);
const parentTypeConstraint = parentType && mapType(parentType, getBaseConstraintOrType);
if (parentTypeConstraint && parentTypeConstraint.flags & TypeFlags.Union && !(rootDeclaration.kind === SyntaxKind.Parameter && isSomeSymbolAssigned(rootDeclaration))) {
const pattern = declaration.parent;
const narrowedType = getFlowTypeOfReference(pattern, parentTypeConstraint, parentTypeConstraint, /*flowContainer*/ undefined, location.flowNode);
if (narrowedType.flags & TypeFlags.Never) {
return neverType;
}
// Destructurings are validated against the parent type elsewhere. Here we disable tuple bounds
// checks because the narrowed type may have lower arity than the full parent type. For example,
// for the declaration [x, y]: [1, 2] | [3], we may have narrowed the parent type to just [3].
return getBindingElementTypeFromParentType(declaration, narrowedType, /*noTupleBoundsCheck*/ true);
}
}
}
Expand Down
3 changes: 1 addition & 2 deletions src/compiler/types.ts
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Expand Up @@ -6240,8 +6240,7 @@ export const enum NodeCheckFlags {
ConstructorReference = 1 << 29, // Binding to a class constructor inside of the class's body.
ContainsClassWithPrivateIdentifiers = 1 << 20, // Marked on all block-scoped containers containing a class with private identifiers.
ContainsSuperPropertyInStaticInitializer = 1 << 21, // Marked on all block-scoped containers containing a static initializer with 'super.x' or 'super[x]'.
InCheckIdentifier = 1 << 22,
PartiallyTypeChecked = 1 << 23, // Node has been partially type checked
PartiallyTypeChecked = 1 << 22, // Node has been partially type checked

/** These flags are LazyNodeCheckFlags and can be calculated lazily by `hasNodeCheckFlag` */
LazyFlags = SuperInstance
Expand Down
24 changes: 24 additions & 0 deletions tests/baselines/reference/dependentDestructuredVariablesNoCrash1.errors.txt
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@@ -0,0 +1,24 @@
dependentDestructuredVariablesNoCrash1.ts(3,10): error TS7010: 'f', which lacks return-type annotation, implicitly has an 'any' return type.
dependentDestructuredVariablesNoCrash1.ts(5,12): error TS1015: Parameter cannot have question mark and initializer.
dependentDestructuredVariablesNoCrash1.ts(5,12): error TS2488: Type '(() => any) | undefined' must have a '[Symbol.iterator]()' method that returns an iterator.
dependentDestructuredVariablesNoCrash1.ts(5,20): error TS7022: 'undefined' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer.
dependentDestructuredVariablesNoCrash1.ts(5,45): error TS2373: Parameter '[first, undefined]' cannot reference identifier 'undefined' declared after it.


==== dependentDestructuredVariablesNoCrash1.ts (5 errors) ====
// https://github.com/microsoft/TypeScript/issues/63044

function f()
~
!!! error TS7010: 'f', which lacks return-type annotation, implicitly has an 'any' return type.

function f([first, undefined]?: () => any = undefined) {}
~~~~~~~~~~~~~~~~~~
!!! error TS1015: Parameter cannot have question mark and initializer.
~~~~~~~~~~~~~~~~~~
!!! error TS2488: Type '(() => any) | undefined' must have a '[Symbol.iterator]()' method that returns an iterator.
~~~~~~~~~
!!! error TS7022: 'undefined' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer.
~~~~~~~~~
!!! error TS2373: Parameter '[first, undefined]' cannot reference identifier 'undefined' declared after it.

18 changes: 18 additions & 0 deletions tests/baselines/reference/dependentDestructuredVariablesNoCrash1.js
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@@ -0,0 +1,18 @@
//// [tests/cases/conformance/controlFlow/dependentDestructuredVariablesNoCrash1.ts] ////

//// [dependentDestructuredVariablesNoCrash1.ts]
// https://github.com/microsoft/TypeScript/issues/63044

function f()

function f([first, undefined]?: () => any = undefined) {}


//// [dependentDestructuredVariablesNoCrash1.js]
"use strict";
// https://github.com/microsoft/TypeScript/issues/63044
function f([first, undefined] = undefined) { }


//// [dependentDestructuredVariablesNoCrash1.d.ts]
declare function f(): any;
14 changes: 14 additions & 0 deletions tests/baselines/reference/dependentDestructuredVariablesNoCrash1.symbols
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@@ -0,0 +1,14 @@
//// [tests/cases/conformance/controlFlow/dependentDestructuredVariablesNoCrash1.ts] ////

=== dependentDestructuredVariablesNoCrash1.ts ===
// https://github.com/microsoft/TypeScript/issues/63044

function f()
>f : Symbol(f, Decl(dependentDestructuredVariablesNoCrash1.ts, 0, 0), Decl(dependentDestructuredVariablesNoCrash1.ts, 2, 12))

function f([first, undefined]?: () => any = undefined) {}
>f : Symbol(f, Decl(dependentDestructuredVariablesNoCrash1.ts, 0, 0), Decl(dependentDestructuredVariablesNoCrash1.ts, 2, 12))
>first : Symbol(first, Decl(dependentDestructuredVariablesNoCrash1.ts, 4, 12))
>undefined : Symbol(undefined, Decl(dependentDestructuredVariablesNoCrash1.ts, 4, 18))
>undefined : Symbol(undefined, Decl(dependentDestructuredVariablesNoCrash1.ts, 4, 18))

19 changes: 19 additions & 0 deletions tests/baselines/reference/dependentDestructuredVariablesNoCrash1.types
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//// [tests/cases/conformance/controlFlow/dependentDestructuredVariablesNoCrash1.ts] ////

=== dependentDestructuredVariablesNoCrash1.ts ===
// https://github.com/microsoft/TypeScript/issues/63044

function f()
>f : () => any
> : ^^^^^^^^^

function f([first, undefined]?: () => any = undefined) {}
>f : () => any
> : ^^^^^^^^^
>first : any
> : ^^^
>undefined : any
> : ^^^
>undefined : any
> : ^^^

25 changes: 25 additions & 0 deletions tests/baselines/reference/dependentDestructuredVariablesNoCrash2.errors.txt
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dependentDestructuredVariablesNoCrash2.ts(3,9): error TS7010: '(Missing)', which lacks return-type annotation, implicitly has an 'any' return type.
dependentDestructuredVariablesNoCrash2.ts(3,10): error TS1003: Identifier expected.
dependentDestructuredVariablesNoCrash2.ts(3,11): error TS2488: Type 'string | undefined' must have a '[Symbol.iterator]()' method that returns an iterator.
dependentDestructuredVariablesNoCrash2.ts(3,11): error TS2371: A parameter initializer is only allowed in a function or constructor implementation.
dependentDestructuredVariablesNoCrash2.ts(3,12): error TS7022: 'undefined' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer.
dependentDestructuredVariablesNoCrash2.ts(3,54): error TS2373: Parameter '[undefined, unknown]' cannot reference identifier 'undefined' declared after it.


==== dependentDestructuredVariablesNoCrash2.ts (6 errors) ====
// https://github.com/microsoft/TypeScript/issues/63091

function ([undefined, unknown]: string | undefined = undefined)

!!! error TS7010: '(Missing)', which lacks return-type annotation, implicitly has an 'any' return type.
~
!!! error TS1003: Identifier expected.
~~~~~~~~~~~~~~~~~~~~
!!! error TS2488: Type 'string | undefined' must have a '[Symbol.iterator]()' method that returns an iterator.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
!!! error TS2371: A parameter initializer is only allowed in a function or constructor implementation.
~~~~~~~~~
!!! error TS7022: 'undefined' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer.
~~~~~~~~~
!!! error TS2373: Parameter '[undefined, unknown]' cannot reference identifier 'undefined' declared after it.

15 changes: 15 additions & 0 deletions tests/baselines/reference/dependentDestructuredVariablesNoCrash2.js
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//// [tests/cases/conformance/controlFlow/dependentDestructuredVariablesNoCrash2.ts] ////

//// [dependentDestructuredVariablesNoCrash2.ts]
// https://github.com/microsoft/TypeScript/issues/63091

function ([undefined, unknown]: string | undefined = undefined)


//// [dependentDestructuredVariablesNoCrash2.js]
"use strict";
// https://github.com/microsoft/TypeScript/issues/63091


//// [dependentDestructuredVariablesNoCrash2.d.ts]
declare function ([undefined, unknown]?: string | undefined): any;
11 changes: 11 additions & 0 deletions tests/baselines/reference/dependentDestructuredVariablesNoCrash2.symbols
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//// [tests/cases/conformance/controlFlow/dependentDestructuredVariablesNoCrash2.ts] ////

=== dependentDestructuredVariablesNoCrash2.ts ===
// https://github.com/microsoft/TypeScript/issues/63091

function ([undefined, unknown]: string | undefined = undefined)
> : Symbol((Missing), Decl(dependentDestructuredVariablesNoCrash2.ts, 0, 0))
>undefined : Symbol(undefined, Decl(dependentDestructuredVariablesNoCrash2.ts, 2, 11))
>unknown : Symbol(unknown, Decl(dependentDestructuredVariablesNoCrash2.ts, 2, 21))
>undefined : Symbol(undefined, Decl(dependentDestructuredVariablesNoCrash2.ts, 2, 11))

15 changes: 15 additions & 0 deletions tests/baselines/reference/dependentDestructuredVariablesNoCrash2.types
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//// [tests/cases/conformance/controlFlow/dependentDestructuredVariablesNoCrash2.ts] ////

=== dependentDestructuredVariablesNoCrash2.ts ===
// https://github.com/microsoft/TypeScript/issues/63091

function ([undefined, unknown]: string | undefined = undefined)
> : ([undefined, unknown]?: string | undefined) => any
> : ^ ^^^ ^^^^^^^^
>undefined : any
> : ^^^
>unknown : any
> : ^^^
>undefined : any
> : ^^^

26 changes: 26 additions & 0 deletions tests/baselines/reference/dependentDestructuredVariablesNoCrash3.errors.txt
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dependentDestructuredVariablesNoCrash3.ts(3,7): error TS2488: Type 'boolean' must have a '[Symbol.iterator]()' method that returns an iterator.
dependentDestructuredVariablesNoCrash3.ts(3,30): error TS7022: 'string' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer.
dependentDestructuredVariablesNoCrash3.ts(3,69): error TS2582: Cannot find name 'test'. Do you need to install type definitions for a test runner? Try `npm i --save-dev @types/jest` or `npm i --save-dev @types/mocha`.
dependentDestructuredVariablesNoCrash3.ts(3,86): error TS2448: Block-scoped variable 'string' used before its declaration.
dependentDestructuredVariablesNoCrash3.ts(3,95): error TS1109: Expression expected.
dependentDestructuredVariablesNoCrash3.ts(3,97): error TS2339: Property 'ranges' does not exist on type 'boolean'.


==== dependentDestructuredVariablesNoCrash3.ts (6 errors) ====
// https://github.com/microsoft/TypeScript/issues/63093

const [r0Def, r0, r1Def, as, string, r1, r2, r3Def, r3]: boolean = (test as number < string > ).ranges();
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
!!! error TS2488: Type 'boolean' must have a '[Symbol.iterator]()' method that returns an iterator.
~~~~~~
!!! error TS7022: 'string' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer.
~~~~
!!! error TS2582: Cannot find name 'test'. Do you need to install type definitions for a test runner? Try `npm i --save-dev @types/jest` or `npm i --save-dev @types/mocha`.
~~~~~~
!!! error TS2448: Block-scoped variable 'string' used before its declaration.
!!! related TS2728 dependentDestructuredVariablesNoCrash3.ts:3:30: 'string' is declared here.
~
!!! error TS1109: Expression expected.
~~~~~~
!!! error TS2339: Property 'ranges' does not exist on type 'boolean'.

16 changes: 16 additions & 0 deletions tests/baselines/reference/dependentDestructuredVariablesNoCrash3.js
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//// [tests/cases/conformance/controlFlow/dependentDestructuredVariablesNoCrash3.ts] ////

//// [dependentDestructuredVariablesNoCrash3.ts]
// https://github.com/microsoft/TypeScript/issues/63093

const [r0Def, r0, r1Def, as, string, r1, r2, r3Def, r3]: boolean = (test as number < string > ).ranges();


//// [dependentDestructuredVariablesNoCrash3.js]
"use strict";
// https://github.com/microsoft/TypeScript/issues/63093
const [r0Def, r0, r1Def, as, string, r1, r2, r3Def, r3] = (test < string > ).ranges();


//// [dependentDestructuredVariablesNoCrash3.d.ts]
declare const r0Def: any, r0: any, r1Def: any, as: any, string: any, r1: any, r2: any, r3Def: any, r3: any;
17 changes: 17 additions & 0 deletions tests/baselines/reference/dependentDestructuredVariablesNoCrash3.symbols
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//// [tests/cases/conformance/controlFlow/dependentDestructuredVariablesNoCrash3.ts] ////

=== dependentDestructuredVariablesNoCrash3.ts ===
// https://github.com/microsoft/TypeScript/issues/63093

const [r0Def, r0, r1Def, as, string, r1, r2, r3Def, r3]: boolean = (test as number < string > ).ranges();
>r0Def : Symbol(r0Def, Decl(dependentDestructuredVariablesNoCrash3.ts, 2, 7))
>r0 : Symbol(r0, Decl(dependentDestructuredVariablesNoCrash3.ts, 2, 13))
>r1Def : Symbol(r1Def, Decl(dependentDestructuredVariablesNoCrash3.ts, 2, 17))
>as : Symbol(as, Decl(dependentDestructuredVariablesNoCrash3.ts, 2, 24))
>string : Symbol(string, Decl(dependentDestructuredVariablesNoCrash3.ts, 2, 28))
>r1 : Symbol(r1, Decl(dependentDestructuredVariablesNoCrash3.ts, 2, 36))
>r2 : Symbol(r2, Decl(dependentDestructuredVariablesNoCrash3.ts, 2, 40))
>r3Def : Symbol(r3Def, Decl(dependentDestructuredVariablesNoCrash3.ts, 2, 44))
>r3 : Symbol(r3, Decl(dependentDestructuredVariablesNoCrash3.ts, 2, 51))
>string : Symbol(string, Decl(dependentDestructuredVariablesNoCrash3.ts, 2, 28))

45 changes: 45 additions & 0 deletions tests/baselines/reference/dependentDestructuredVariablesNoCrash3.types
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//// [tests/cases/conformance/controlFlow/dependentDestructuredVariablesNoCrash3.ts] ////

=== dependentDestructuredVariablesNoCrash3.ts ===
// https://github.com/microsoft/TypeScript/issues/63093

const [r0Def, r0, r1Def, as, string, r1, r2, r3Def, r3]: boolean = (test as number < string > ).ranges();
>r0Def : any
> : ^^^
>r0 : any
> : ^^^
>r1Def : any
> : ^^^
>as : any
> : ^^^
>string : any
> : ^^^
>r1 : any
> : ^^^
>r2 : any
> : ^^^
>r3Def : any
> : ^^^
>r3 : any
> : ^^^
>(test as number < string > ).ranges() : any
> : ^^^
>(test as number < string > ).ranges : any
> : ^^^
>(test as number < string > ) : boolean
> : ^^^^^^^
>test as number < string > : boolean
> : ^^^^^^^
>test as number < string : boolean
> : ^^^^^^^
>test as number : number
> : ^^^^^^
>test : any
> : ^^^
>string : any
> : ^^^
> : any
> : ^^^
>ranges : any
> : ^^^

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