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Merged
merged 2 commits into from
Sep 28, 2025
+182 −7
Merged

Types with extra properties are never subtypes of fresh object literals #1759

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444fc87
Types with extra properties are never subtypes of fresh object literals
ahejlsberg Sep 28, 2025
eeba5ca
Add tests
ahejlsberg Sep 28, 2025
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11 changes: 4 additions & 7 deletions internal/checker/relater.go
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Original file line number Diff line number Diff line change
Expand Up @@ -4153,16 +4153,13 @@ func (r *Relater) propertiesRelatedTo(source *Type, target *Type, reportErrors b
}
return TernaryFalse
}
if isObjectLiteralType(target) {
if target.objectFlags&ObjectFlagsFreshLiteral != 0 {
for _, sourceProp := range excludeProperties(r.c.getPropertiesOfType(source), excludedProperties) {
if r.c.getPropertyOfObjectType(target, sourceProp.Name) == nil {
sourceType := r.c.getTypeOfSymbol(sourceProp)
if sourceType.flags&TypeFlagsUndefined == 0 {
if reportErrors {
r.reportError(diagnostics.Property_0_does_not_exist_on_type_1, r.c.symbolToString(sourceProp), r.c.TypeToString(target))
}
return TernaryFalse
if reportErrors {
r.reportError(diagnostics.Property_0_does_not_exist_on_type_1, r.c.symbolToString(sourceProp), r.c.TypeToString(target))
}
return TernaryFalse
}
}
}
Comment on lines +4156 to 4165
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Copilot AI Sep 28, 2025

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The excess property checking logic has been simplified but the removal of the undefined type check may be too broad. The previous logic if sourceType.flags&TypeFlagsUndefined == 0 ensured that undefined properties weren't considered excess properties, which might be important for optional property handling. Consider whether this check should be preserved to maintain correct behavior for optional properties.

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This is intended.

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65 changes: 65 additions & 0 deletions testdata/baselines/reference/compiler/freshObjectLiteralSubtype.symbols
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@@ -0,0 +1,65 @@
//// [tests/cases/compiler/freshObjectLiteralSubtype.ts] ////

=== freshObjectLiteralSubtype.ts ===
function f1() {
>f1 : Symbol(f1, Decl(freshObjectLiteralSubtype.ts, 0, 0))

if (!!true) {
return { valid: true }
>valid : Symbol(valid, Decl(freshObjectLiteralSubtype.ts, 2, 16))
}
return f2()
>f2 : Symbol(f2, Decl(freshObjectLiteralSubtype.ts, 7, 13))
}

declare const f2: () => { valid: boolean, msg?: undefined }
>f2 : Symbol(f2, Decl(freshObjectLiteralSubtype.ts, 7, 13))
>valid : Symbol(valid, Decl(freshObjectLiteralSubtype.ts, 7, 25))
>msg : Symbol(msg, Decl(freshObjectLiteralSubtype.ts, 7, 41))

f1().msg
>f1().msg : Symbol(msg, Decl(freshObjectLiteralSubtype.ts, 7, 41))
>f1 : Symbol(f1, Decl(freshObjectLiteralSubtype.ts, 0, 0))
>msg : Symbol(msg, Decl(freshObjectLiteralSubtype.ts, 7, 41))

// Repro from https://github.com/microsoft/typescript-go/issues/1742

function validate() {
>validate : Symbol(validate, Decl(freshObjectLiteralSubtype.ts, 9, 8))

if(Math.random() > 0.5) {
>Math.random : Symbol(Math.random, Decl(lib.es5.d.ts, --, --))
>Math : Symbol(Math, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>random : Symbol(Math.random, Decl(lib.es5.d.ts, --, --))

return utilValidate();
>utilValidate : Symbol(utilValidate, Decl(freshObjectLiteralSubtype.ts, 18, 2))
}
return { valid: true };
>valid : Symbol(valid, Decl(freshObjectLiteralSubtype.ts, 17, 12))

};


declare function utilValidate(): {
>utilValidate : Symbol(utilValidate, Decl(freshObjectLiteralSubtype.ts, 18, 2))

valid: boolean;
>valid : Symbol(valid, Decl(freshObjectLiteralSubtype.ts, 21, 34))

msg?: undefined;
>msg : Symbol(msg, Decl(freshObjectLiteralSubtype.ts, 22, 19))

} | {
valid: boolean;
>valid : Symbol(valid, Decl(freshObjectLiteralSubtype.ts, 24, 5))

msg: string;
>msg : Symbol(msg, Decl(freshObjectLiteralSubtype.ts, 25, 19))
}

validate().msg; // Error in TSGO
>validate().msg : Symbol(msg, Decl(freshObjectLiteralSubtype.ts, 22, 19), Decl(freshObjectLiteralSubtype.ts, 25, 19))
>validate : Symbol(validate, Decl(freshObjectLiteralSubtype.ts, 9, 8))
>msg : Symbol(msg, Decl(freshObjectLiteralSubtype.ts, 22, 19), Decl(freshObjectLiteralSubtype.ts, 25, 19))

80 changes: 80 additions & 0 deletions testdata/baselines/reference/compiler/freshObjectLiteralSubtype.types
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@@ -0,0 +1,80 @@
//// [tests/cases/compiler/freshObjectLiteralSubtype.ts] ////

=== freshObjectLiteralSubtype.ts ===
function f1() {
>f1 : () => { valid: boolean; msg?: undefined; }

if (!!true) {
>!!true : true
>!true : false
>true : true

return { valid: true }
>{ valid: true } : { valid: boolean; }
>valid : boolean
>true : true
}
return f2()
>f2() : { valid: boolean; msg?: undefined; }
>f2 : () => { valid: boolean; msg?: undefined; }
}

declare const f2: () => { valid: boolean, msg?: undefined }
>f2 : () => { valid: boolean; msg?: undefined; }
>valid : boolean
>msg : undefined

f1().msg
>f1().msg : undefined
>f1() : { valid: boolean; msg?: undefined; }
>f1 : () => { valid: boolean; msg?: undefined; }
>msg : undefined

// Repro from https://github.com/microsoft/typescript-go/issues/1742

function validate() {
>validate : () => { valid: boolean; msg?: undefined; } | { valid: boolean; msg: string; }

if(Math.random() > 0.5) {
>Math.random() > 0.5 : boolean
>Math.random() : number
>Math.random : () => number
>Math : Math
>random : () => number
>0.5 : 0.5

return utilValidate();
>utilValidate() : { valid: boolean; msg?: undefined; } | { valid: boolean; msg: string; }
>utilValidate : () => { valid: boolean; msg?: undefined; } | { valid: boolean; msg: string; }
}
return { valid: true };
>{ valid: true } : { valid: boolean; }
>valid : boolean
>true : true

};


declare function utilValidate(): {
>utilValidate : () => { valid: boolean; msg?: undefined; } | { valid: boolean; msg: string; }

valid: boolean;
>valid : boolean

msg?: undefined;
>msg : undefined

} | {
valid: boolean;
>valid : boolean

msg: string;
>msg : string
}

validate().msg; // Error in TSGO
>validate().msg : string | undefined
>validate() : { valid: boolean; msg?: undefined; } | { valid: boolean; msg: string; }
>validate : () => { valid: boolean; msg?: undefined; } | { valid: boolean; msg: string; }
>msg : string | undefined

33 changes: 33 additions & 0 deletions testdata/tests/cases/compiler/freshObjectLiteralSubtype.ts
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@@ -0,0 +1,33 @@
// @strict: true
// @noEmit: true

function f1() {
if (!!true) {
return { valid: true }
}
return f2()
}

declare const f2: () => { valid: boolean, msg?: undefined }

f1().msg

// Repro from https://github.com/microsoft/typescript-go/issues/1742

function validate() {
if(Math.random() > 0.5) {
return utilValidate();
}
return { valid: true };
};


declare function utilValidate(): {
valid: boolean;
msg?: undefined;
} | {
valid: boolean;
msg: string;
}

validate().msg; // Error in TSGO
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