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[experiment] tsgo compat changes #62556

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185d2cb
tsgo compat changes
jakebailey Oct 6, 2025
a44a434
Accept baselines
jakebailey Oct 6, 2025
d163960
Update fourslash tests
jakebailey Oct 6, 2025
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413 changes: 403 additions & 10 deletions src/compiler/checker.ts
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10 changes: 6 additions & 4 deletions src/compiler/core.ts
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Expand Up @@ -1209,7 +1209,7 @@ export function binarySearchKey<T, U>(array: readonly T[], key: U, keySelector:
while (low <= high) {
const middle = low + ((high - low) >> 1);
const midKey = keySelector(array[middle], middle);
switch (keyComparer(midKey, key)) {
switch (Math.sign(keyComparer(midKey, key))) {
case Comparison.LessThan:
low = middle + 1;
break;
Expand Down Expand Up @@ -1967,9 +1967,11 @@ export function equateStringsCaseSensitive(a: string, b: string): boolean {
return equateValues(a, b);
}

function compareComparableValues(a: string | undefined, b: string | undefined): Comparison;
function compareComparableValues(a: number | undefined, b: number | undefined): Comparison;
function compareComparableValues(a: string | number | undefined, b: string | number | undefined) {
/** @internal */
export function compareComparableValues(a: string | undefined, b: string | undefined): Comparison;
/** @internal */
export function compareComparableValues(a: number | undefined, b: number | undefined): Comparison;
export function compareComparableValues(a: string | number | undefined, b: string | number | undefined) {
return a === b ? Comparison.EqualTo :
a === undefined ? Comparison.LessThan :
b === undefined ? Comparison.GreaterThan :
Expand Down
5 changes: 5 additions & 0 deletions src/compiler/corePublic.ts
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Expand Up @@ -5,6 +5,11 @@ export const versionMajorMinor = "6.0";
/** The version of the TypeScript compiler release */
export const version: string = `${versionMajorMinor}.0-dev`;

const tsgoCompatEnv = typeof process !== "undefined" && process.env ? process.env.TSGO_COMPAT : undefined;

/** @internal */
export const TSGO_COMPAT: boolean = tsgoCompatEnv ? tsgoCompatEnv === "true" : true;

/**
* Type of objects whose values are all of the same type.
* The `in` and `for-in` operators can *not* be safely used,
Expand Down
73 changes: 41 additions & 32 deletions src/compiler/types.ts
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Expand Up @@ -6319,42 +6319,49 @@ export interface SerializedTypeEntry {
trackedSymbols: readonly TrackedSymbol[] | undefined;
}

// Note that for types of different kinds, the numeric values of TypeFlags determine the order
// computed by the CompareTypes function and therefore the order of constituent types in union types.
// Since union type processing often bails out early when a result is known, it is important to order
// TypeFlags in increasing order of potential type complexity. In particular, indexed access and
// conditional types should sort last as those types are potentially recursive and possibly infinite.

// dprint-ignore
export const enum TypeFlags {
Any = 1 << 0,
Unknown = 1 << 1,
String = 1 << 2,
Number = 1 << 3,
Boolean = 1 << 4,
Enum = 1 << 5, // Numeric computed enum member value
BigInt = 1 << 6,
StringLiteral = 1 << 7,
NumberLiteral = 1 << 8,
BooleanLiteral = 1 << 9,
EnumLiteral = 1 << 10, // Always combined with StringLiteral, NumberLiteral, or Union
BigIntLiteral = 1 << 11,
ESSymbol = 1 << 12, // Type of symbol primitive introduced in ES6
UniqueESSymbol = 1 << 13, // unique symbol
Void = 1 << 14,
Undefined = 1 << 15,
Null = 1 << 16,
Never = 1 << 17, // Never type
TypeParameter = 1 << 18, // Type parameter
Object = 1 << 19, // Object type
Union = 1 << 20, // Union (T | U)
Intersection = 1 << 21, // Intersection (T & U)
Index = 1 << 22, // keyof T
IndexedAccess = 1 << 23, // T[K]
Conditional = 1 << 24, // T extends U ? X : Y
Substitution = 1 << 25, // Type parameter substitution
NonPrimitive = 1 << 26, // intrinsic object type
TemplateLiteral = 1 << 27, // Template literal type
StringMapping = 1 << 28, // Uppercase/Lowercase type
Undefined = 1 << 2,
Null = 1 << 3,
Void = 1 << 4,
String = 1 << 5,
Number = 1 << 6,
BigInt = 1 << 7,
Boolean = 1 << 8,
ESSymbol = 1 << 9, // Type of symbol primitive introduced in ES6
StringLiteral = 1 << 10,
NumberLiteral = 1 << 11,
BigIntLiteral = 1 << 12,
BooleanLiteral = 1 << 13,
UniqueESSymbol = 1 << 14, // unique symbol
EnumLiteral = 1 << 15, // Always combined with StringLiteral, NumberLiteral, or Union
Enum = 1 << 16, // Numeric computed enum member value (must be right after EnumLiteral, see getSortOrderFlags)
NonPrimitive = 1 << 17, // intrinsic object type
Never = 1 << 18, // Never type
TypeParameter = 1 << 19, // Type parameter
Object = 1 << 20, // Object type
Index = 1 << 21, // keyof T
TemplateLiteral = 1 << 22, // Template literal type
StringMapping = 1 << 23, // Uppercase/Lowercase type
Substitution = 1 << 24, // Type parameter substitution
IndexedAccess = 1 << 25, // T[K]
Conditional = 1 << 26, // T extends U ? X : Y
Union = 1 << 27, // Union (T | U)
Intersection = 1 << 28, // Intersection (T & U)
/** @internal */
Reserved1 = 1 << 29, // Used by union/intersection type construction
/** @internal */
Reserved2 = 1 << 30, // Used by union/intersection type construction

/** @internal */
Reserved3 = 1 << 31,
/** @internal */
AnyOrUnknown = Any | Unknown,
/** @internal */
Expand Down Expand Up @@ -6538,14 +6545,16 @@ export const enum ObjectFlags {
PropagatingFlags = ContainsWideningType | ContainsObjectOrArrayLiteral | NonInferrableType,
/** @internal */
InstantiatedMapped = Mapped | Instantiated,
// Object flags that uniquely identify the kind of ObjectType
/** @internal */
ObjectTypeKindMask = ClassOrInterface | Reference | Tuple | Anonymous | Mapped | ReverseMapped | EvolvingArray,


// Flags that require TypeFlags.Object
ContainsSpread = 1 << 21, // Object literal contains spread operation
ObjectRestType = 1 << 22, // Originates in object rest declaration
InstantiationExpressionType = 1 << 23, // Originates in instantiation expression

// Object flags that uniquely identify the kind of ObjectType
/** @internal */
ObjectTypeKindMask = ClassOrInterface | Reference | Tuple | Anonymous | Mapped | ReverseMapped | EvolvingArray | InstantiationExpressionType | SingleSignatureType,

/** @internal */
IsClassInstanceClone = 1 << 24, // Type is a clone of a class instance type
// Flags that require TypeFlags.Object and ObjectFlags.Reference
Expand Down
4 changes: 2 additions & 2 deletions tests/baselines/reference/TypeGuardWithArrayUnion.types
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Expand Up @@ -13,13 +13,13 @@ class Message {
function saySize(message: Message | Message[]) {
>saySize : (message: Message | Message[]) => number
> : ^ ^^ ^^^^^^^^^^^
>message : Message | Message[]
>message : Message[] | Message
> : ^^^^^^^^^^^^^^^^^^^

if (message instanceof Array) {
>message instanceof Array : boolean
> : ^^^^^^^
>message : Message | Message[]
>message : Message[] | Message
> : ^^^^^^^^^^^^^^^^^^^
>Array : ArrayConstructor
> : ^^^^^^^^^^^^^^^^
Expand Down
22 changes: 11 additions & 11 deletions tests/baselines/reference/TypeGuardWithEnumUnion.types
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Expand Up @@ -20,7 +20,7 @@ function f1(x: Color | string) {
if (typeof x === "number") {
>typeof x === "number" : boolean
> : ^^^^^^^
>typeof x : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
>typeof x : "bigint" | "boolean" | "function" | "number" | "object" | "string" | "symbol" | "undefined"
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>x : string | Color
> : ^^^^^^^^^^^^^^
Expand Down Expand Up @@ -53,15 +53,15 @@ function f1(x: Color | string) {
function f2(x: Color | string | string[]) {
>f2 : (x: Color | string | string[]) => void
> : ^ ^^ ^^^^^^^^^
>x : string | Color | string[]
>x : string | string[] | Color
> : ^^^^^^^^^^^^^^^^^^^^^^^^^

if (typeof x === "object") {
>typeof x === "object" : boolean
> : ^^^^^^^
>typeof x : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
>typeof x : "bigint" | "boolean" | "function" | "number" | "object" | "string" | "symbol" | "undefined"
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>x : string | Color | string[]
>x : string | string[] | Color
> : ^^^^^^^^^^^^^^^^^^^^^^^^^
>"object" : "object"
> : ^^^^^^^^
Expand All @@ -79,9 +79,9 @@ function f2(x: Color | string | string[]) {
if (typeof x === "number") {
>typeof x === "number" : boolean
> : ^^^^^^^
>typeof x : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
>typeof x : "bigint" | "boolean" | "function" | "number" | "object" | "string" | "symbol" | "undefined"
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>x : string | Color | string[]
>x : string | string[] | Color
> : ^^^^^^^^^^^^^^^^^^^^^^^^^
>"number" : "number"
> : ^^^^^^^^
Expand Down Expand Up @@ -110,9 +110,9 @@ function f2(x: Color | string | string[]) {
if (typeof x === "string") {
>typeof x === "string" : boolean
> : ^^^^^^^
>typeof x : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
>typeof x : "bigint" | "boolean" | "function" | "number" | "object" | "string" | "symbol" | "undefined"
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>x : string | Color | string[]
>x : string | string[] | Color
> : ^^^^^^^^^^^^^^^^^^^^^^^^^
>"string" : "string"
> : ^^^^^^^^
Expand All @@ -129,13 +129,13 @@ function f2(x: Color | string | string[]) {
}
else {
var b = x;
>b : Color | string[]
>b : string[] | Color
> : ^^^^^^^^^^^^^^^^
>x : Color | string[]
>x : string[] | Color
> : ^^^^^^^^^^^^^^^^

var b: Color | string[];
>b : Color | string[]
>b : string[] | Color
> : ^^^^^^^^^^^^^^^^
}
}
Expand Down
4 changes: 2 additions & 2 deletions tests/baselines/reference/ambientExportDefaultErrors.types
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Expand Up @@ -41,7 +41,7 @@ declare module "indirect" {
> : ^^^^^^^^^^^^^^^^^^^^^^^^^

export default typeof Foo.default;
>typeof Foo.default : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
>typeof Foo.default : "bigint" | "boolean" | "function" | "number" | "object" | "string" | "symbol" | "undefined"
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>Foo.default : number
> : ^^^^^^
Expand All @@ -58,7 +58,7 @@ declare module "indirect2" {
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^

export = typeof Foo2;
>typeof Foo2 : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
>typeof Foo2 : "bigint" | "boolean" | "function" | "number" | "object" | "string" | "symbol" | "undefined"
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>Foo2 : number
> : ^^^^^^
Expand Down
2 changes: 1 addition & 1 deletion tests/baselines/reference/anonymousClassExpression1.types
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Expand Up @@ -8,7 +8,7 @@ function f() {
return typeof class {} === "function";
>typeof class {} === "function" : boolean
> : ^^^^^^^
>typeof class {} : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
>typeof class {} : "bigint" | "boolean" | "function" | "number" | "object" | "string" | "symbol" | "undefined"
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>class {} : typeof (Anonymous class)
> : ^^^^^^^^^^^^^^^^^^^^^^^^
Expand Down
94 changes: 47 additions & 47 deletions tests/baselines/reference/api/typescript.d.ts
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Expand Up @@ -6591,53 +6591,53 @@ declare namespace ts {
enum TypeFlags {
Any = 1,
Unknown = 2,
String = 4,
Number = 8,
Boolean = 16,
Enum = 32,
BigInt = 64,
StringLiteral = 128,
NumberLiteral = 256,
BooleanLiteral = 512,
EnumLiteral = 1024,
BigIntLiteral = 2048,
ESSymbol = 4096,
UniqueESSymbol = 8192,
Void = 16384,
Undefined = 32768,
Null = 65536,
Never = 131072,
TypeParameter = 262144,
Object = 524288,
Union = 1048576,
Intersection = 2097152,
Index = 4194304,
IndexedAccess = 8388608,
Conditional = 16777216,
Substitution = 33554432,
NonPrimitive = 67108864,
TemplateLiteral = 134217728,
StringMapping = 268435456,
Literal = 2944,
Unit = 109472,
Freshable = 2976,
StringOrNumberLiteral = 384,
PossiblyFalsy = 117724,
StringLike = 402653316,
NumberLike = 296,
BigIntLike = 2112,
BooleanLike = 528,
EnumLike = 1056,
ESSymbolLike = 12288,
VoidLike = 49152,
UnionOrIntersection = 3145728,
StructuredType = 3670016,
TypeVariable = 8650752,
InstantiableNonPrimitive = 58982400,
InstantiablePrimitive = 406847488,
Instantiable = 465829888,
StructuredOrInstantiable = 469499904,
Narrowable = 536624127,
Undefined = 4,
Null = 8,
Void = 16,
String = 32,
Number = 64,
BigInt = 128,
Boolean = 256,
ESSymbol = 512,
StringLiteral = 1024,
NumberLiteral = 2048,
BigIntLiteral = 4096,
BooleanLiteral = 8192,
UniqueESSymbol = 16384,
EnumLiteral = 32768,
Enum = 65536,
NonPrimitive = 131072,
Never = 262144,
TypeParameter = 524288,
Object = 1048576,
Index = 2097152,
TemplateLiteral = 4194304,
StringMapping = 8388608,
Substitution = 16777216,
IndexedAccess = 33554432,
Conditional = 67108864,
Union = 134217728,
Intersection = 268435456,
Literal = 15360,
Unit = 97292,
Freshable = 80896,
StringOrNumberLiteral = 3072,
PossiblyFalsy = 15868,
StringLike = 12583968,
NumberLike = 67648,
BigIntLike = 4224,
BooleanLike = 8448,
EnumLike = 98304,
ESSymbolLike = 16896,
VoidLike = 20,
UnionOrIntersection = 402653184,
StructuredType = 403701760,
TypeVariable = 34078720,
InstantiableNonPrimitive = 117964800,
InstantiablePrimitive = 14680064,
Instantiable = 132644864,
StructuredOrInstantiable = 536346624,
Narrowable = 536575971,
}
type DestructuringPattern = BindingPattern | ObjectLiteralExpression | ArrayLiteralExpression;
interface Type {
Expand Down
20 changes: 12 additions & 8 deletions tests/baselines/reference/arityAndOrderCompatibility01.errors.txt
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Expand Up @@ -11,14 +11,16 @@ arityAndOrderCompatibility01.ts(23,5): error TS2322: Type '{ 0: string; 1: numbe
arityAndOrderCompatibility01.ts(24,5): error TS2322: Type '[string, number]' is not assignable to type '[number]'.
Source has 2 element(s) but target allows only 1.
arityAndOrderCompatibility01.ts(25,5): error TS2322: Type 'StrNum' is not assignable to type '[number]'.
Types of property '0' are incompatible.
Type 'string' is not assignable to type 'number'.
The types returned by 'pop()' are incompatible between these types.
Type 'string | number' is not assignable to type 'number'.
Type 'string' is not assignable to type 'number'.
arityAndOrderCompatibility01.ts(26,5): error TS2322: Type '{ 0: string; 1: number; length: 2; }' is not assignable to type '[number]'.
arityAndOrderCompatibility01.ts(27,5): error TS2322: Type '[string, number]' is not assignable to type '[string]'.
Source has 2 element(s) but target allows only 1.
arityAndOrderCompatibility01.ts(28,5): error TS2322: Type 'StrNum' is not assignable to type '[string]'.
Types of property 'length' are incompatible.
Type '2' is not assignable to type '1'.
The types returned by 'pop()' are incompatible between these types.
Type 'string | number' is not assignable to type 'string'.
Type 'number' is not assignable to type 'string'.
arityAndOrderCompatibility01.ts(29,5): error TS2322: Type '{ 0: string; 1: number; length: 2; }' is not assignable to type '[string]'.
arityAndOrderCompatibility01.ts(30,5): error TS2322: Type '[string, number]' is not assignable to type '[number, string]'.
Type at position 0 in source is not compatible with type at position 0 in target.
Expand Down Expand Up @@ -78,8 +80,9 @@ arityAndOrderCompatibility01.ts(32,5): error TS2322: Type '{ 0: string; 1: numbe
var l2: [number] = y;
~~
!!! error TS2322: Type 'StrNum' is not assignable to type '[number]'.
!!! error TS2322: Types of property '0' are incompatible.
!!! error TS2322: Type 'string' is not assignable to type 'number'.
!!! error TS2322: The types returned by 'pop()' are incompatible between these types.
!!! error TS2322: Type 'string | number' is not assignable to type 'number'.
!!! error TS2322: Type 'string' is not assignable to type 'number'.
var l3: [number] = z;
~~
!!! error TS2322: Type '{ 0: string; 1: number; length: 2; }' is not assignable to type '[number]'.
Expand All @@ -90,8 +93,9 @@ arityAndOrderCompatibility01.ts(32,5): error TS2322: Type '{ 0: string; 1: numbe
var m2: [string] = y;
~~
!!! error TS2322: Type 'StrNum' is not assignable to type '[string]'.
!!! error TS2322: Types of property 'length' are incompatible.
!!! error TS2322: Type '2' is not assignable to type '1'.
!!! error TS2322: The types returned by 'pop()' are incompatible between these types.
!!! error TS2322: Type 'string | number' is not assignable to type 'string'.
!!! error TS2322: Type 'number' is not assignable to type 'string'.
var m3: [string] = z;
~~
!!! error TS2322: Type '{ 0: string; 1: number; length: 2; }' is not assignable to type '[string]'.
Expand Down
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