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ahejlsberg merged 9 commits into from
Apr 30, 2026
Merged

Fix checks for disallowed property/accessor duplicate declarations #3672

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9704812
Fix checks for disallowed property/accessor duplicate declarations
ahejlsberg Apr 30, 2026
32e7dcd
Accept new baselines
ahejlsberg Apr 30, 2026
b8a0a55
Accessors take precedence over properties
ahejlsberg Apr 30, 2026
dee9069
Disallow duplicate method/property declarations in object literals
ahejlsberg Apr 30, 2026
714ae7d
Accept new baselines
ahejlsberg Apr 30, 2026
4aeb37c
Update submoduleAccepted.txt
ahejlsberg Apr 30, 2026
9b0938e
Generate enums
ahejlsberg Apr 30, 2026
bc129e1
Add regression test
ahejlsberg Apr 30, 2026
4afaaa4
Move new diffs to accepted bucket
ahejlsberg Apr 30, 2026
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8 changes: 4 additions & 4 deletions _packages/native-preview/src/enums/symbolFlags.enum.ts
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Expand Up @@ -44,7 +44,7 @@ export enum SymbolFlags {
FunctionScopedVariableExcludes = Value & ~FunctionScopedVariable,
BlockScopedVariableExcludes = Value,
ParameterExcludes = Value,
PropertyExcludes = Value & ~Property,
PropertyExcludes = Value & ~(Property | Accessor),
EnumMemberExcludes = Value | Type,
FunctionExcludes = Value & ~(Function | ValueModule | Class),
ClassExcludes = (Value | Type) & ~(ValueModule | Interface | Function),
Expand All @@ -54,9 +54,9 @@ export enum SymbolFlags {
ValueModuleExcludes = Value & ~(Function | Class | RegularEnum | ValueModule),
NamespaceModuleExcludes = None,
MethodExcludes = Value & ~Method,
GetAccessorExcludes = Value & ~SetAccessor,
SetAccessorExcludes = Value & ~GetAccessor,
AccessorExcludes = Value,
GetAccessorExcludes = Value & ~(SetAccessor | Property),
SetAccessorExcludes = Value & ~(GetAccessor | Property),
AccessorExcludes = Value & ~Property,
TypeParameterExcludes = Type & ~TypeParameter,
TypeAliasExcludes = Type,
AliasExcludes = Alias,
Expand Down
8 changes: 4 additions & 4 deletions _packages/native-preview/src/enums/symbolFlags.ts
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Expand Up @@ -44,7 +44,7 @@ export var SymbolFlags: any;
SymbolFlags[SymbolFlags["FunctionScopedVariableExcludes"] = 111550] = "FunctionScopedVariableExcludes";
SymbolFlags[SymbolFlags["BlockScopedVariableExcludes"] = 111551] = "BlockScopedVariableExcludes";
SymbolFlags[SymbolFlags["ParameterExcludes"] = 111551] = "ParameterExcludes";
SymbolFlags[SymbolFlags["PropertyExcludes"] = 111547] = "PropertyExcludes";
SymbolFlags[SymbolFlags["PropertyExcludes"] = 13243] = "PropertyExcludes";
SymbolFlags[SymbolFlags["EnumMemberExcludes"] = 900095] = "EnumMemberExcludes";
SymbolFlags[SymbolFlags["FunctionExcludes"] = 110991] = "FunctionExcludes";
SymbolFlags[SymbolFlags["ClassExcludes"] = 899503] = "ClassExcludes";
Expand All @@ -54,9 +54,9 @@ export var SymbolFlags: any;
SymbolFlags[SymbolFlags["ValueModuleExcludes"] = 110735] = "ValueModuleExcludes";
SymbolFlags[SymbolFlags["NamespaceModuleExcludes"] = 0] = "NamespaceModuleExcludes";
SymbolFlags[SymbolFlags["MethodExcludes"] = 103359] = "MethodExcludes";
SymbolFlags[SymbolFlags["GetAccessorExcludes"] = 46015] = "GetAccessorExcludes";
SymbolFlags[SymbolFlags["SetAccessorExcludes"] = 78783] = "SetAccessorExcludes";
SymbolFlags[SymbolFlags["AccessorExcludes"] = 111551] = "AccessorExcludes";
SymbolFlags[SymbolFlags["GetAccessorExcludes"] = 46011] = "GetAccessorExcludes";
SymbolFlags[SymbolFlags["SetAccessorExcludes"] = 78779] = "SetAccessorExcludes";
SymbolFlags[SymbolFlags["AccessorExcludes"] = 111547] = "AccessorExcludes";
SymbolFlags[SymbolFlags["TypeParameterExcludes"] = 526824] = "TypeParameterExcludes";
SymbolFlags[SymbolFlags["TypeAliasExcludes"] = 788968] = "TypeAliasExcludes";
SymbolFlags[SymbolFlags["AliasExcludes"] = 2097152] = "AliasExcludes";
Expand Down
8 changes: 4 additions & 4 deletions internal/ast/symbolflags.go
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Expand Up @@ -56,7 +56,7 @@ const (
SymbolFlagsBlockScopedVariableExcludes = SymbolFlagsValue

SymbolFlagsParameterExcludes = SymbolFlagsValue
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These exclusion-mask changes are subtle and directly impact binding/merging semantics (especially around property/accessor merging being allowed in the binder and rejected later in the checker). Please add a short comment near these constants explaining the rationale and the intended invariants (e.g., “binder allows property+accessor merge; checker reports duplicates within the same declaration”), so future modifications don’t inadvertently revert the intended behavior.

Suggested change
SymbolFlagsParameterExcludes = SymbolFlagsValue
SymbolFlagsParameterExcludes = SymbolFlagsValue
// Binder intentionally allows property+accessor merges by not excluding Property/Accessor
// here; duplicate/conflicting declarations within the same declaration are reported later
// by the checker. Keep these masks aligned so future changes do not tighten binder merging.

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SymbolFlagsPropertyExcludes = SymbolFlagsValue & ^SymbolFlagsProperty
SymbolFlagsPropertyExcludes = SymbolFlagsValue & ^(SymbolFlagsProperty | SymbolFlagsAccessor)
SymbolFlagsEnumMemberExcludes = SymbolFlagsValue | SymbolFlagsType
SymbolFlagsFunctionExcludes = SymbolFlagsValue & ^(SymbolFlagsFunction | SymbolFlagsValueModule | SymbolFlagsClass)
SymbolFlagsClassExcludes = (SymbolFlagsValue | SymbolFlagsType) & ^(SymbolFlagsValueModule | SymbolFlagsInterface | SymbolFlagsFunction) // class-interface mergability done in checker.ts
Expand All @@ -66,9 +66,9 @@ const (
SymbolFlagsValueModuleExcludes = SymbolFlagsValue & ^(SymbolFlagsFunction | SymbolFlagsClass | SymbolFlagsRegularEnum | SymbolFlagsValueModule)
SymbolFlagsNamespaceModuleExcludes = SymbolFlagsNone
SymbolFlagsMethodExcludes = SymbolFlagsValue & ^SymbolFlagsMethod
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These exclusion-mask changes are subtle and directly impact binding/merging semantics (especially around property/accessor merging being allowed in the binder and rejected later in the checker). Please add a short comment near these constants explaining the rationale and the intended invariants (e.g., “binder allows property+accessor merge; checker reports duplicates within the same declaration”), so future modifications don’t inadvertently revert the intended behavior.

Suggested change
SymbolFlagsMethodExcludes = SymbolFlagsValue & ^SymbolFlagsMethod
SymbolFlagsMethodExcludes = SymbolFlagsValue & ^SymbolFlagsMethod
// Binder intentionally allows property+accessor merges by excluding accessors from
// other value declarations but not from properties. The checker later reports duplicate
// or otherwise invalid combinations within the same declaration.

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SymbolFlagsGetAccessorExcludes = SymbolFlagsValue & ^SymbolFlagsSetAccessor
SymbolFlagsSetAccessorExcludes = SymbolFlagsValue & ^SymbolFlagsGetAccessor
SymbolFlagsAccessorExcludes = SymbolFlagsValue
SymbolFlagsGetAccessorExcludes = SymbolFlagsValue & ^(SymbolFlagsSetAccessor | SymbolFlagsProperty)
SymbolFlagsSetAccessorExcludes = SymbolFlagsValue & ^(SymbolFlagsGetAccessor | SymbolFlagsProperty)
SymbolFlagsAccessorExcludes = SymbolFlagsValue & ^SymbolFlagsProperty
SymbolFlagsTypeParameterExcludes = SymbolFlagsType & ^SymbolFlagsTypeParameter
SymbolFlagsTypeAliasExcludes = SymbolFlagsType
SymbolFlagsAliasExcludes = SymbolFlagsAlias
Expand Down
2 changes: 1 addition & 1 deletion internal/binder/binder.go
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Expand Up @@ -665,7 +665,7 @@ func (b *Binder) bind(node *ast.Node) bool {
case ast.KindCallSignature, ast.KindConstructSignature, ast.KindIndexSignature:
b.declareSymbolAndAddToSymbolTable(node, ast.SymbolFlagsSignature, ast.SymbolFlagsNone)
case ast.KindMethodDeclaration, ast.KindMethodSignature:
b.bindPropertyOrMethodOrAccessor(node, ast.SymbolFlagsMethod|getOptionalSymbolFlagForNode(node), core.IfElse(ast.IsObjectLiteralMethod(node), ast.SymbolFlagsPropertyExcludes, ast.SymbolFlagsMethodExcludes))
b.bindPropertyOrMethodOrAccessor(node, ast.SymbolFlagsMethod|getOptionalSymbolFlagForNode(node), core.IfElse(ast.IsObjectLiteralMethod(node), ast.SymbolFlagsValue, ast.SymbolFlagsMethodExcludes))
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Switching object-literal methods to use ast.SymbolFlagsValue as the exclude mask is a behavioral change that can affect merging between object-literal methods and same-named properties/accessors (and therefore inferred object literal types and diagnostics). Please add/extend a baseline test that covers at least { a() {}, get a() { ... } } and { a() {}, a: 1 } to ensure the binder+checker combination still produces the intended error codes and inferred member type.

Suggested change
b.bindPropertyOrMethodOrAccessor(node, ast.SymbolFlagsMethod|getOptionalSymbolFlagForNode(node), core.IfElse(ast.IsObjectLiteralMethod(node), ast.SymbolFlagsValue, ast.SymbolFlagsMethodExcludes))
b.bindPropertyOrMethodOrAccessor(node, ast.SymbolFlagsMethod|getOptionalSymbolFlagForNode(node), ast.SymbolFlagsMethodExcludes)

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@ahejlsberg ahejlsberg Apr 30, 2026

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The tests already show the effects of this change (i.e. method names must be unique in object literals).

case ast.KindFunctionDeclaration:
b.bindFunctionDeclaration(node)
case ast.KindConstructor:
Expand Down
33 changes: 20 additions & 13 deletions internal/checker/checker.go
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Expand Up @@ -3081,7 +3081,7 @@ func (c *Checker) checkObjectTypeForDuplicateDeclarations(node *ast.Node, checkP
var staticNames map[string]int
var privateNames map[string]int
nodeInAmbientContext := node.Flags&ast.NodeFlagsAmbient != 0
checkProperty := func(symbol *ast.Symbol, isStatic bool) {
checkPropertyOrAccessor := func(symbol *ast.Symbol, kind int, isStatic bool) {
if len(symbol.Declarations) > 1 {
var names map[string]int
if isStatic {
Expand All @@ -3095,19 +3095,24 @@ func (c *Checker) checkObjectTypeForDuplicateDeclarations(node *ast.Node, checkP
}
names = instanceNames
}
if state := names[symbol.Name]; state != 2 {
if state == 1 {
c.reportDuplicateMemberErrors(node, symbol.Name, true, isStatic, diagnostics.Duplicate_identifier_0)
}
names[symbol.Name] = state + 1
state := names[symbol.Name]
switch {
case state == 0:
// On first occurrence just record the kind
names[symbol.Name] = kind
case state == 1 || state == 2 && kind != 2:
// Error on second property or combination of property and accessor
c.reportDuplicateMemberErrors(node, symbol.Name, true, isStatic, diagnostics.Duplicate_identifier_0)
// Record that errors have been reported
names[symbol.Name] = 3
}
}
}
for _, member := range node.Members() {
if ast.IsConstructorDeclaration(member) {
for _, param := range member.Parameters() {
if ast.IsParameterPropertyDeclaration(param, member) && !ast.IsBindingPattern(param.Name()) {
checkProperty(c.getSymbolOfDeclaration(param), false /*isStatic*/)
checkPropertyOrAccessor(c.getSymbolOfDeclaration(param), 1, false /*isStatic*/)
}
}
} else {
Expand All @@ -3117,10 +3122,12 @@ func (c *Checker) checkObjectTypeForDuplicateDeclarations(node *ast.Node, checkP
if !nodeInAmbientContext && isStatic && symbol != nil && symbol.Name == "prototype" {
c.error(member.Name(), diagnostics.Static_property_0_conflicts_with_built_in_property_Function_0_of_constructor_function_1, symbol.Name, c.symbolToString(c.getSymbolOfDeclaration(node)))
}
// When a property has multiple declarations, check that only one of those declarations is in this object
// type declaration (multiple merged object types are permitted to each declare the same property).
// Check that this object type declaration doesn't contain multiple declarations of the same property,
// or accessor and property declarations with the same name.
if ast.IsPropertyDeclaration(member) && !ast.HasAccessorModifier(member) || ast.IsPropertySignatureDeclaration(member) {
checkProperty(symbol, isStatic)
checkPropertyOrAccessor(symbol, 1, isStatic)
} else if ast.IsAccessor(member) || ast.IsPropertyDeclaration(member) && ast.HasAccessorModifier(member) {
checkPropertyOrAccessor(symbol, 2, isStatic)
}
// Check that each private identifier is used only for instance members or only for static members. It is an
// error for an instance and a static member to have the same private identifier.
Expand Down Expand Up @@ -16118,6 +16125,9 @@ func (c *Checker) getTypeOfSymbol(symbol *ast.Symbol) *Type {
if symbol.CheckFlags&ast.CheckFlagsReverseMapped != 0 {
return c.getTypeOfReverseMappedSymbol(symbol)
}
if symbol.Flags&ast.SymbolFlagsAccessor != 0 {
return c.getTypeOfAccessors(symbol)
}
if symbol.Flags&(ast.SymbolFlagsVariable|ast.SymbolFlagsProperty) != 0 {
return c.getTypeOfVariableOrParameterOrProperty(symbol)
}
Expand All @@ -16127,9 +16137,6 @@ func (c *Checker) getTypeOfSymbol(symbol *ast.Symbol) *Type {
if symbol.Flags&ast.SymbolFlagsEnumMember != 0 {
return c.getTypeOfEnumMember(symbol)
}
if symbol.Flags&ast.SymbolFlagsAccessor != 0 {
return c.getTypeOfAccessors(symbol)
}
if symbol.Flags&ast.SymbolFlagsAlias != 0 {
return c.getTypeOfAlias(symbol)
}
Expand Down
84 changes: 31 additions & 53 deletions testdata/baselines/reference/compiler/duplicateIdentifierChecks.errors.txt
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Expand Up @@ -58,14 +58,8 @@ duplicateIdentifierChecks.ts(114,9): error TS2300: Duplicate identifier 'x'.
duplicateIdentifierChecks.ts(115,9): error TS2300: Duplicate identifier 'x'.
duplicateIdentifierChecks.ts(116,9): error TS1118: An object literal cannot have multiple get/set accessors with the same name.
duplicateIdentifierChecks.ts(116,9): error TS2300: Duplicate identifier 'x'.
duplicateIdentifierChecks.ts(120,9): error TS2300: Duplicate identifier 'x'.
duplicateIdentifierChecks.ts(121,5): error TS1119: An object literal cannot have property and accessor with the same name.
duplicateIdentifierChecks.ts(121,5): error TS2300: Duplicate identifier 'x'.
duplicateIdentifierChecks.ts(122,9): error TS2300: Duplicate identifier 'x'.
duplicateIdentifierChecks.ts(126,9): error TS2300: Duplicate identifier 'x'.
duplicateIdentifierChecks.ts(127,5): error TS1119: An object literal cannot have property and accessor with the same name.
duplicateIdentifierChecks.ts(127,5): error TS2300: Duplicate identifier 'x'.
duplicateIdentifierChecks.ts(128,9): error TS2300: Duplicate identifier 'x'.
duplicateIdentifierChecks.ts(132,9): error TS2300: Duplicate identifier 'x'.
duplicateIdentifierChecks.ts(133,5): error TS1119: An object literal cannot have property and accessor with the same name.
duplicateIdentifierChecks.ts(133,5): error TS2300: Duplicate identifier 'x'.
Expand All @@ -74,12 +68,12 @@ duplicateIdentifierChecks.ts(138,9): error TS2300: Duplicate identifier 'x'.
duplicateIdentifierChecks.ts(139,5): error TS1119: An object literal cannot have property and accessor with the same name.
duplicateIdentifierChecks.ts(139,5): error TS2300: Duplicate identifier 'x'.
duplicateIdentifierChecks.ts(140,9): error TS2300: Duplicate identifier 'x'.
duplicateIdentifierChecks.ts(146,9): error TS2300: Duplicate identifier 'foo'.
duplicateIdentifierChecks.ts(147,5): error TS2300: Duplicate identifier 'foo'.
duplicateIdentifierChecks.ts(148,9): error TS2300: Duplicate identifier 'foo'.
duplicateIdentifierChecks.ts(152,9): error TS2300: Duplicate identifier '[foo]'.
duplicateIdentifierChecks.ts(153,5): error TS2300: Duplicate identifier '[foo]'.
duplicateIdentifierChecks.ts(154,9): error TS2300: Duplicate identifier '[foo]'.
duplicateIdentifierChecks.ts(146,9): error TS2300: Duplicate identifier '[foo]'.
duplicateIdentifierChecks.ts(147,5): error TS2300: Duplicate identifier '[foo]'.
duplicateIdentifierChecks.ts(148,9): error TS2300: Duplicate identifier '[foo]'.
duplicateIdentifierChecks.ts(152,9): error TS2300: Duplicate identifier 'foo'.
duplicateIdentifierChecks.ts(153,5): error TS2300: Duplicate identifier 'foo'.
duplicateIdentifierChecks.ts(154,9): error TS2300: Duplicate identifier 'foo'.
duplicateIdentifierChecks.ts(158,9): error TS2300: Duplicate identifier '[foo]'.
duplicateIdentifierChecks.ts(159,9): error TS2300: Duplicate identifier '[foo]'.
duplicateIdentifierChecks.ts(160,9): error TS2300: Duplicate identifier '[foo]'.
Expand All @@ -91,15 +85,15 @@ duplicateIdentifierChecks.ts(171,5): error TS2300: Duplicate identifier 'foo'.
duplicateIdentifierChecks.ts(175,5): error TS2300: Duplicate identifier 'foo'.
duplicateIdentifierChecks.ts(176,5): error TS2300: Duplicate identifier 'foo'.
duplicateIdentifierChecks.ts(177,5): error TS2300: Duplicate identifier 'foo'.
duplicateIdentifierChecks.ts(181,9): error TS2300: Duplicate identifier 'foo'.
duplicateIdentifierChecks.ts(182,5): error TS2300: Duplicate identifier 'foo'.
duplicateIdentifierChecks.ts(183,9): error TS2300: Duplicate identifier 'foo'.
duplicateIdentifierChecks.ts(187,5): error TS2300: Duplicate identifier 'foo'.
duplicateIdentifierChecks.ts(188,9): error TS2300: Duplicate identifier 'foo'.
duplicateIdentifierChecks.ts(189,9): error TS2300: Duplicate identifier 'foo'.
duplicateIdentifierChecks.ts(193,9): error TS2300: Duplicate identifier 'foo'.
duplicateIdentifierChecks.ts(194,9): error TS2300: Duplicate identifier 'foo'.
duplicateIdentifierChecks.ts(195,5): error TS2300: Duplicate identifier 'foo'.
duplicateIdentifierChecks.ts(181,9): error TS2300: Duplicate identifier '[foo]'.
duplicateIdentifierChecks.ts(182,5): error TS2300: Duplicate identifier '[foo]'.
duplicateIdentifierChecks.ts(183,9): error TS2300: Duplicate identifier '[foo]'.
duplicateIdentifierChecks.ts(187,5): error TS2300: Duplicate identifier '[foo]'.
duplicateIdentifierChecks.ts(188,9): error TS2300: Duplicate identifier '[foo]'.
duplicateIdentifierChecks.ts(189,9): error TS2300: Duplicate identifier '[foo]'.
duplicateIdentifierChecks.ts(193,9): error TS2300: Duplicate identifier '[foo]'.
duplicateIdentifierChecks.ts(194,9): error TS2300: Duplicate identifier '[foo]'.
duplicateIdentifierChecks.ts(195,5): error TS2300: Duplicate identifier '[foo]'.
duplicateIdentifierChecks.ts(201,9): error TS2300: Duplicate identifier '[sym]'.
duplicateIdentifierChecks.ts(202,5): error TS2300: Duplicate identifier '[sym]'.
duplicateIdentifierChecks.ts(203,9): error TS2300: Duplicate identifier '[sym]'.
Expand All @@ -108,7 +102,7 @@ duplicateIdentifierChecks.ts(208,5): error TS2300: Duplicate identifier '[sym]'.
duplicateIdentifierChecks.ts(209,9): error TS2300: Duplicate identifier '[sym]'.


==== duplicateIdentifierChecks.ts (108 errors) ====
==== duplicateIdentifierChecks.ts (102 errors) ====
// Every member declaration in the following should produce a duplicate identifier error.

interface I1 {
Expand Down Expand Up @@ -349,30 +343,18 @@ duplicateIdentifierChecks.ts(209,9): error TS2300: Duplicate identifier '[sym]'.

const o5 = {
get x() { return 0 },
~
!!! error TS2300: Duplicate identifier 'x'.
x: 0,
~
!!! error TS1119: An object literal cannot have property and accessor with the same name.
~
!!! error TS2300: Duplicate identifier 'x'.
set x(value: number) { }
~
!!! error TS2300: Duplicate identifier 'x'.
}

const o6 = {
set x(value: number) { },
~
!!! error TS2300: Duplicate identifier 'x'.
x: 0,
~
!!! error TS1119: An object literal cannot have property and accessor with the same name.
~
!!! error TS2300: Duplicate identifier 'x'.
get x() { return 0 }
~
!!! error TS2300: Duplicate identifier 'x'.
}

const o7 = {
Expand Down Expand Up @@ -408,29 +390,25 @@ duplicateIdentifierChecks.ts(209,9): error TS2300: Duplicate identifier '[sym]'.
interface I10 {
get [foo](): number;
~~~~~
!!! error TS2300: Duplicate identifier 'foo'.
!!! error TS2300: Duplicate identifier '[foo]'.
[foo]: number;
~~~~~
!!! error TS2300: Duplicate identifier 'foo'.
!!! error TS2300: Duplicate identifier '[foo]'.
set [foo](value: number);
~~~~~
!!! error TS2300: Duplicate identifier 'foo'.
!!! error TS2300: Duplicate identifier '[foo]'.
}

interface I11 {
get [foo](): number;
~~~~~
!!! error TS2300: Duplicate identifier '[foo]'.
!!! related TS6203 duplicateIdentifierChecks.ts:153:5: '[foo]' was also declared here.
!!! error TS2300: Duplicate identifier 'foo'.
foo: number;
~~~
!!! error TS2300: Duplicate identifier '[foo]'.
!!! related TS6203 duplicateIdentifierChecks.ts:152:9: '[foo]' was also declared here.
!!! related TS6204 duplicateIdentifierChecks.ts:154:9: and here.
!!! error TS2300: Duplicate identifier 'foo'.
set [foo](value: number);
~~~~~
!!! error TS2300: Duplicate identifier '[foo]'.
!!! related TS6203 duplicateIdentifierChecks.ts:153:5: '[foo]' was also declared here.
!!! error TS2300: Duplicate identifier 'foo'.
}

interface I12 {
Expand Down Expand Up @@ -485,37 +463,37 @@ duplicateIdentifierChecks.ts(209,9): error TS2300: Duplicate identifier '[sym]'.
declare class C10 {
get [foo](): number;
~~~~~
!!! error TS2300: Duplicate identifier 'foo'.
!!! error TS2300: Duplicate identifier '[foo]'.
[foo]: number;
~~~~~
!!! error TS2300: Duplicate identifier 'foo'.
!!! error TS2300: Duplicate identifier '[foo]'.
set [foo](value: number);
~~~~~
!!! error TS2300: Duplicate identifier 'foo'.
!!! error TS2300: Duplicate identifier '[foo]'.
}

declare class C11 {
[foo]: number;
~~~~~
!!! error TS2300: Duplicate identifier 'foo'.
!!! error TS2300: Duplicate identifier '[foo]'.
get [foo](): number;
~~~~~
!!! error TS2300: Duplicate identifier 'foo'.
!!! error TS2300: Duplicate identifier '[foo]'.
set [foo](value: number);
~~~~~
!!! error TS2300: Duplicate identifier 'foo'.
!!! error TS2300: Duplicate identifier '[foo]'.
}

declare class C12 {
get [foo](): number;
~~~~~
!!! error TS2300: Duplicate identifier 'foo'.
!!! error TS2300: Duplicate identifier '[foo]'.
set [foo](value: number);
~~~~~
!!! error TS2300: Duplicate identifier 'foo'.
!!! error TS2300: Duplicate identifier '[foo]'.
[foo]: number;
~~~~~
!!! error TS2300: Duplicate identifier 'foo'.
!!! error TS2300: Duplicate identifier '[foo]'.
}

const sym = Symbol();
Expand Down
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