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Backport tsgo PR 3301 for testing #63328

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6 changes: 3 additions & 3 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -25499,12 +25499,12 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {

function getSingleCommonSupertype(types: Type[]) {
// First, find the leftmost type for which no type to the right is a strict supertype, and if that
// type is a strict supertype of all other candidates, return it. Otherwise, return the leftmost type
// for which no type to the right is a (regular) supertype.
// type is a strict supertype of all other candidates, return it. Otherwise, use asymmetric
// assignability as a tiebreaker (i.e. only switch candidates when the assignment is one-way).
const candidate = reduceLeft(types, (s, t) => isTypeStrictSubtypeOf(s, t) ? t : s)!;
return every(types, t => t === candidate || isTypeStrictSubtypeOf(t, candidate)) ?
candidate :
reduceLeft(types, (s, t) => isTypeSubtypeOf(s, t) ? t : s)!;
reduceLeft(types, (s, t) => isTypeAssignableTo(s, t) && !isTypeAssignableTo(t, s) ? t : s)!;
}

// Return the leftmost type for which no type to the right is a subtype.
Expand Down
48 changes: 48 additions & 0 deletions tests/baselines/reference/discriminatedUnionFlatMap.symbols
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@@ -0,0 +1,48 @@
//// [tests/cases/compiler/discriminatedUnionFlatMap.ts] ////

=== discriminatedUnionFlatMap.ts ===
// https://github.com/microsoft/typescript-go/issues/1057

export type InputOp = { op: "add" } | { op: "remove"; value?: Array<unknown> };
>InputOp : Symbol(InputOp, Decl(discriminatedUnionFlatMap.ts, 0, 0))
>op : Symbol(op, Decl(discriminatedUnionFlatMap.ts, 2, 23))
>op : Symbol(op, Decl(discriminatedUnionFlatMap.ts, 2, 39))
>value : Symbol(value, Decl(discriminatedUnionFlatMap.ts, 2, 53))
>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 2 more)

export type OutputOp = { op: "add" | "remove" };
>OutputOp : Symbol(OutputOp, Decl(discriminatedUnionFlatMap.ts, 2, 79))
>op : Symbol(op, Decl(discriminatedUnionFlatMap.ts, 3, 24))

export function f(operations: InputOp[]): OutputOp[] {
>f : Symbol(f, Decl(discriminatedUnionFlatMap.ts, 3, 48))
>operations : Symbol(operations, Decl(discriminatedUnionFlatMap.ts, 5, 18))
>InputOp : Symbol(InputOp, Decl(discriminatedUnionFlatMap.ts, 0, 0))
>OutputOp : Symbol(OutputOp, Decl(discriminatedUnionFlatMap.ts, 2, 79))

return operations.flatMap((operation) => {
>operations.flatMap : Symbol(Array.flatMap, Decl(lib.es2019.array.d.ts, --, --))
>operations : Symbol(operations, Decl(discriminatedUnionFlatMap.ts, 5, 18))
>flatMap : Symbol(Array.flatMap, Decl(lib.es2019.array.d.ts, --, --))
>operation : Symbol(operation, Decl(discriminatedUnionFlatMap.ts, 6, 31))

if (operation.op === "remove" && operation.value) {
>operation.op : Symbol(op, Decl(discriminatedUnionFlatMap.ts, 2, 23), Decl(discriminatedUnionFlatMap.ts, 2, 39))
>operation : Symbol(operation, Decl(discriminatedUnionFlatMap.ts, 6, 31))
>op : Symbol(op, Decl(discriminatedUnionFlatMap.ts, 2, 23), Decl(discriminatedUnionFlatMap.ts, 2, 39))
>operation.value : Symbol(value, Decl(discriminatedUnionFlatMap.ts, 2, 53))
>operation : Symbol(operation, Decl(discriminatedUnionFlatMap.ts, 6, 31))
>value : Symbol(value, Decl(discriminatedUnionFlatMap.ts, 2, 53))

return [].map(() => ({ op: "remove" }));
>[].map : Symbol(Array.map, Decl(lib.es5.d.ts, --, --))
>map : Symbol(Array.map, Decl(lib.es5.d.ts, --, --))
>op : Symbol(op, Decl(discriminatedUnionFlatMap.ts, 8, 34))

} else {
return [operation];
>operation : Symbol(operation, Decl(discriminatedUnionFlatMap.ts, 6, 31))
}
});
}

91 changes: 91 additions & 0 deletions tests/baselines/reference/discriminatedUnionFlatMap.types
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@@ -0,0 +1,91 @@
//// [tests/cases/compiler/discriminatedUnionFlatMap.ts] ////

=== discriminatedUnionFlatMap.ts ===
// https://github.com/microsoft/typescript-go/issues/1057

export type InputOp = { op: "add" } | { op: "remove"; value?: Array<unknown> };
>InputOp : InputOp
> : ^^^^^^^
>op : "add"
> : ^^^^^
>op : "remove"
> : ^^^^^^^^
>value : unknown[] | undefined
> : ^^^^^^^^^^^^^^^^^^^^^

export type OutputOp = { op: "add" | "remove" };
>OutputOp : OutputOp
> : ^^^^^^^^
>op : "add" | "remove"
> : ^^^^^^^^^^^^^^^^

export function f(operations: InputOp[]): OutputOp[] {
>f : (operations: InputOp[]) => OutputOp[]
> : ^ ^^ ^^^^^
>operations : InputOp[]
> : ^^^^^^^^^

return operations.flatMap((operation) => {
>operations.flatMap((operation) => { if (operation.op === "remove" && operation.value) { return [].map(() => ({ op: "remove" })); } else { return [operation]; } }) : InputOp[]
> : ^^^^^^^^^
>operations.flatMap : <U, This = undefined>(callback: (this: This, value: InputOp, index: number, array: InputOp[]) => U | readonly U[], thisArg?: This | undefined) => U[]
> : ^ ^^ ^^^^^^^^^^^^^^ ^^^ ^^^^^^^^ ^^^^^^^^^^^ ^^ ^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^
>operations : InputOp[]
> : ^^^^^^^^^
>flatMap : <U, This = undefined>(callback: (this: This, value: InputOp, index: number, array: InputOp[]) => U | readonly U[], thisArg?: This | undefined) => U[]
> : ^ ^^ ^^^^^^^^^^^^^^ ^^^ ^^^^^^^^ ^^^^^^^^^^^ ^^ ^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^
>(operation) => { if (operation.op === "remove" && operation.value) { return [].map(() => ({ op: "remove" })); } else { return [operation]; } } : (this: undefined, operation: InputOp) => InputOp[] | { op: "remove"; }[]
> : ^ ^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>operation : InputOp
> : ^^^^^^^

if (operation.op === "remove" && operation.value) {
>operation.op === "remove" && operation.value : false | unknown[] | undefined
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>operation.op === "remove" : boolean
> : ^^^^^^^
>operation.op : "add" | "remove"
> : ^^^^^^^^^^^^^^^^
>operation : InputOp
> : ^^^^^^^
>op : "add" | "remove"
> : ^^^^^^^^^^^^^^^^
>"remove" : "remove"
> : ^^^^^^^^
>operation.value : unknown[] | undefined
> : ^^^^^^^^^^^^^^^^^^^^^
>operation : { op: "remove"; value?: Array<unknown>; }
> : ^^^^^^ ^^^^^^^^^^ ^^^
>value : unknown[] | undefined
> : ^^^^^^^^^^^^^^^^^^^^^

return [].map(() => ({ op: "remove" }));
>[].map(() => ({ op: "remove" })) : { op: "remove"; }[]
> : ^^^^^^^^^^^^^^^^^^^
>[].map : <U>(callbackfn: (value: never, index: number, array: never[]) => U, thisArg?: any) => U[]
> : ^ ^^ ^^^ ^^^^^^^^^ ^^ ^^ ^^^^^^^^^^^^^^^^^ ^^^ ^^^^^^^^
>[] : never[]
> : ^^^^^^^
>map : <U>(callbackfn: (value: never, index: number, array: never[]) => U, thisArg?: any) => U[]
> : ^ ^^ ^^^ ^^^^^^^^^ ^^ ^^ ^^^^^^^^^^^^^^^^^ ^^^ ^^^^^^^^
>() => ({ op: "remove" }) : () => { op: "remove"; }
> : ^^^^^^^^^^^^^^^^^^^^^^^
>({ op: "remove" }) : { op: "remove"; }
> : ^^^^^^^^^^^^^^^^^
>{ op: "remove" } : { op: "remove"; }
> : ^^^^^^^^^^^^^^^^^
>op : "remove"
> : ^^^^^^^^
>"remove" : "remove"
> : ^^^^^^^^

} else {
return [operation];
>[operation] : InputOp[]
> : ^^^^^^^^^
>operation : InputOp
> : ^^^^^^^
}
});
}

18 changes: 18 additions & 0 deletions tests/cases/compiler/discriminatedUnionFlatMap.ts
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@@ -0,0 +1,18 @@
// @strict: true
// @noEmit: true
// @lib: es2019

// https://github.com/microsoft/typescript-go/issues/1057

export type InputOp = { op: "add" } | { op: "remove"; value?: Array<unknown> };
export type OutputOp = { op: "add" | "remove" };

export function f(operations: InputOp[]): OutputOp[] {
return operations.flatMap((operation) => {
if (operation.op === "remove" && operation.value) {
return [].map(() => ({ op: "remove" }));
} else {
return [operation];
}
});
}
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