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Dedupe identical object literal types before subtype reduction #64729

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0144957
Dedupe identical object literal types before subtype reduction
gadcam Oct 10, 2026
822cd37
Only use already resolved members for the shape key; add regression test
gadcam Oct 10, 2026
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63 changes: 63 additions & 0 deletions tsc/internal/checker/checker.go
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if cached := c.subtypeReductionCache[key]; cached != nil {
return cached
}
if hasObjectTypes {
types = c.removeIdenticalObjectLiteralTypes(types)
}
// We assume that redundant primitive types have already been removed from the types array and that there
// are no any and unknown types in the array. Thus, the only possible supertypes for primitive types are empty
// object types, and if none of those are present we can exclude primitive types from the subtype check.
Expand Down
return types
}

// removeIdenticalObjectLiteralTypes removes object literal types with the same shape as an earlier type in the list.
// The pairwise loop in removeSubtypes would keep only the first of them anyway, but at a quadratic cost for large
// arrays of records such as imported JSON files.
func (c *Checker) removeIdenticalObjectLiteralTypes(types []*Type) []*Type {
var seen map[CacheHashKey]struct{}
return core.Filter(types, func(t *Type) bool {
key, ok := c.getObjectLiteralShapeKey(t)
if !ok {
return true
}
if _, ok := seen[key]; ok {
return false
}
if seen == nil {
seen = make(map[CacheHashKey]struct{})
}
seen[key] = struct{}{}
return true
})
}

func (c *Checker) getObjectLiteralShapeKey(t *Type) (CacheHashKey, bool) {
// Only use members that are already resolved, so that computing the key never triggers resolution.
if t.flags&TypeFlagsObject == 0 || !isObjectLiteralType(t) || t.objectFlags&ObjectFlagsMembersResolved == 0 {
return CacheHashKey{}, false
}
resolved := t.AsStructuredType()
if len(resolved.signatures) != 0 || len(resolved.indexInfos) != 0 {
return CacheHashKey{}, false
}
var b keyBuilder
b.writeUint32(uint32(t.objectFlags & (ObjectFlagsFreshLiteral | ObjectFlagsJSLiteral | ObjectFlagsContainsSpread | ObjectFlagsObjectLiteralPatternWithComputedProperties)))
b.writeInt(len(resolved.properties))
for _, p := range resolved.properties {
propType := c.getResolvedTypeOfObjectLiteralProperty(p)
if propType == nil {
return CacheHashKey{}, false
}
b.writeInt(len(p.Name()))
b.writeString(p.Name())
b.writeUint32(uint32(p.Flags()))
b.writeUint32(uint32(p.CheckFlags()))
b.writeType(propType)
}
return b.hash(), true
}

// getResolvedTypeOfObjectLiteralProperty returns the type of a plain object literal property only if it is already
// resolved (see #46981).
func (c *Checker) getResolvedTypeOfObjectLiteralProperty(p *ast.Symbol) *Type {
if p.Flags()&(ast.SymbolFlagsAccessor|ast.SymbolFlagsMethod) != 0 ||
p.CheckFlags()&(ast.CheckFlagsDeferredType|ast.CheckFlagsInstantiated|ast.CheckFlagsMapped|ast.CheckFlagsReverseMapped) != 0 {
return nil
}
if links := c.valueSymbolLinks.TryGet(p); links != nil {
return links.resolvedType
}
return nil
}

func (c *Checker) intersectTypes(type1 *Type, type2 *Type) *Type {
switch {
case type1 == nil:
94 changes: 94 additions & 0 deletions ...tdata/baselines/reference/compiler/arrayLiteralIdenticalObjectLiteralsSubtypeReduction.js
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//// [tests/cases/compiler/arrayLiteralIdenticalObjectLiteralsSubtypeReduction.ts] ////

//// [data.json]
[
{ "code": "#f3dc00", "label": "526-G", "name": "Saharagelb" },
{ "code": "#f6ca00", "label": "527-G", "name": "Buttergelb" },
{ "name": "Primelgelb", "label": "504-G", "code": "#ffbe00" },
{ "name": "Rapsgelb", "label": 505, "code": "#ffb000" },
{ "code": "#ff9a00", "label": "506-G", "name": "Maisgelb" },
{ "code": "#ff8200", "label": "507-G", "name": null },
{ "code": "#ff6c00", "label": "508-G", "name": null, "extra": true },
{ "name": "Orangegelb", "label": 509, "code": "#ff5a00" }
]

//// [main.ts]
// https://github.com/microsoft/TypeScript/issues/48364
import data from "./data.json";

export const fromJson = data;

declare const o: { x: number };
declare const n: number;

export const differentOrder = [{ a: 1, b: "" }, { b: "", a: 1 }, { a: 2, b: "x" }];
export const optionalProperties = [{ a: 1, b: n > 0 ? "" : undefined }, { a: 2, b: n > 0 ? "x" : undefined }];
export const spreads = [{ ...o }, { ...o }, { ...o, y: "" }];
export const methods = [{ m() { return 1; } }, { m() { return 2; } }, { m() { return ""; } }];
export const accessors = [{ get a() { return 1; } }, { get a() { return 2; } }, { a: 3 }];
export const constAssertion = [{ a: 1 }, { a: 1 }, { a: 2 }] as const;


//// [main.js]
// https://github.com/microsoft/TypeScript/issues/48364
import data from "./data.json";
export const fromJson = data;
export const differentOrder = [{ a: 1, b: "" }, { b: "", a: 1 }, { a: 2, b: "x" }];
export const optionalProperties = [{ a: 1, b: n > 0 ? "" : undefined }, { a: 2, b: n > 0 ? "x" : undefined }];
export const spreads = [{ ...o }, { ...o }, { ...o, y: "" }];
export const methods = [{ m() { return 1; } }, { m() { return 2; } }, { m() { return ""; } }];
export const accessors = [{ get a() { return 1; } }, { get a() { return 2; } }, { a: 3 }];
export const constAssertion = [{ a: 1 }, { a: 1 }, { a: 2 }];


//// [main.d.ts]
export declare const fromJson: ({
code: string;
label: string;
name: string;
extra?: undefined;
} | {
name: string;
label: number;
code: string;
extra?: undefined;
} | {
code: string;
label: string;
name: null;
extra?: undefined;
} | {
code: string;
label: string;
name: null;
extra: boolean;
})[];
export declare const differentOrder: {
a: number;
b: string;
}[];
export declare const optionalProperties: {
a: number;
b: string | undefined;
}[];
export declare const spreads: ({
x: number;
} | {
x: number;
y: string;
})[];
export declare const methods: ({
m(): number;
} | {
m(): string;
})[];
export declare const accessors: {
readonly a: number;
}[];
export declare const constAssertion: readonly [{
readonly a: 1;
}, {
readonly a: 1;
}, {
readonly a: 2;
}];
109 changes: 109 additions & 0 deletions .../baselines/reference/compiler/arrayLiteralIdenticalObjectLiteralsSubtypeReduction.symbols
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//// [tests/cases/compiler/arrayLiteralIdenticalObjectLiteralsSubtypeReduction.ts] ////

=== /data.json ===
[
{ "code": "#f3dc00", "label": "526-G", "name": "Saharagelb" },
>"code" : Symbol("code", Decl(data.json, 1, 5))
>"label" : Symbol("label", Decl(data.json, 1, 24))
>"name" : Symbol("name", Decl(data.json, 1, 42))

{ "code": "#f6ca00", "label": "527-G", "name": "Buttergelb" },
>"code" : Symbol("code", Decl(data.json, 2, 5))
>"label" : Symbol("label", Decl(data.json, 2, 24))
>"name" : Symbol("name", Decl(data.json, 2, 42))

{ "name": "Primelgelb", "label": "504-G", "code": "#ffbe00" },
>"name" : Symbol("name", Decl(data.json, 3, 5))
>"label" : Symbol("label", Decl(data.json, 3, 27))
>"code" : Symbol("code", Decl(data.json, 3, 45))

{ "name": "Rapsgelb", "label": 505, "code": "#ffb000" },
>"name" : Symbol("name", Decl(data.json, 4, 5))
>"label" : Symbol("label", Decl(data.json, 4, 25))
>"code" : Symbol("code", Decl(data.json, 4, 39))

{ "code": "#ff9a00", "label": "506-G", "name": "Maisgelb" },
>"code" : Symbol("code", Decl(data.json, 5, 5))
>"label" : Symbol("label", Decl(data.json, 5, 24))
>"name" : Symbol("name", Decl(data.json, 5, 42))

{ "code": "#ff8200", "label": "507-G", "name": null },
>"code" : Symbol("code", Decl(data.json, 6, 5))
>"label" : Symbol("label", Decl(data.json, 6, 24))
>"name" : Symbol("name", Decl(data.json, 6, 42))

{ "code": "#ff6c00", "label": "508-G", "name": null, "extra": true },
>"code" : Symbol("code", Decl(data.json, 7, 5))
>"label" : Symbol("label", Decl(data.json, 7, 24))
>"name" : Symbol("name", Decl(data.json, 7, 42))
>"extra" : Symbol("extra", Decl(data.json, 7, 56))

{ "name": "Orangegelb", "label": 509, "code": "#ff5a00" }
>"name" : Symbol("name", Decl(data.json, 8, 5))
>"label" : Symbol("label", Decl(data.json, 8, 27))
>"code" : Symbol("code", Decl(data.json, 8, 41))

]

=== /main.ts ===
// https://github.com/microsoft/TypeScript/issues/48364
import data from "./data.json";
>data : Symbol(data, Decl(main.ts, 1, 6))

export const fromJson = data;
>fromJson : Symbol(fromJson, Decl(main.ts, 3, 12))
>data : Symbol(data, Decl(main.ts, 1, 6))

declare const o: { x: number };
>o : Symbol(o, Decl(main.ts, 5, 13))
>x : Symbol(x, Decl(main.ts, 5, 18))

declare const n: number;
>n : Symbol(n, Decl(main.ts, 6, 13))

export const differentOrder = [{ a: 1, b: "" }, { b: "", a: 1 }, { a: 2, b: "x" }];
>differentOrder : Symbol(differentOrder, Decl(main.ts, 8, 12))
>a : Symbol(a, Decl(main.ts, 8, 32))
>b : Symbol(b, Decl(main.ts, 8, 38))
>b : Symbol(b, Decl(main.ts, 8, 49))
>a : Symbol(a, Decl(main.ts, 8, 56))
>a : Symbol(a, Decl(main.ts, 8, 66))
>b : Symbol(b, Decl(main.ts, 8, 72))

export const optionalProperties = [{ a: 1, b: n > 0 ? "" : undefined }, { a: 2, b: n > 0 ? "x" : undefined }];
>optionalProperties : Symbol(optionalProperties, Decl(main.ts, 9, 12))
>a : Symbol(a, Decl(main.ts, 9, 36))
>b : Symbol(b, Decl(main.ts, 9, 42))
>n : Symbol(n, Decl(main.ts, 6, 13))
>undefined : Symbol(undefined)
>a : Symbol(a, Decl(main.ts, 9, 73))
>b : Symbol(b, Decl(main.ts, 9, 79))
>n : Symbol(n, Decl(main.ts, 6, 13))
>undefined : Symbol(undefined)

export const spreads = [{ ...o }, { ...o }, { ...o, y: "" }];
>spreads : Symbol(spreads, Decl(main.ts, 10, 12))
>o : Symbol(o, Decl(main.ts, 5, 13))
>o : Symbol(o, Decl(main.ts, 5, 13))
>o : Symbol(o, Decl(main.ts, 5, 13))
>y : Symbol(y, Decl(main.ts, 10, 51))

export const methods = [{ m() { return 1; } }, { m() { return 2; } }, { m() { return ""; } }];
>methods : Symbol(methods, Decl(main.ts, 11, 12))
>m : Symbol(m, Decl(main.ts, 11, 25))
>m : Symbol(m, Decl(main.ts, 11, 48))
>m : Symbol(m, Decl(main.ts, 11, 71))

export const accessors = [{ get a() { return 1; } }, { get a() { return 2; } }, { a: 3 }];
>accessors : Symbol(accessors, Decl(main.ts, 12, 12))
>a : Symbol(a, Decl(main.ts, 12, 27))
>a : Symbol(a, Decl(main.ts, 12, 54))
>a : Symbol(a, Decl(main.ts, 12, 81))

export const constAssertion = [{ a: 1 }, { a: 1 }, { a: 2 }] as const;
>constAssertion : Symbol(constAssertion, Decl(main.ts, 13, 12))
>a : Symbol(a, Decl(main.ts, 13, 32))
>a : Symbol(a, Decl(main.ts, 13, 42))
>a : Symbol(a, Decl(main.ts, 13, 52))
>const : Symbol(const)

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