Symbol type is incorrectly generalized when used as ... | microsoft/TypeScript

TypeScript Version: 3.7.5

Search Terms: symbol infer type

Expected behavior:

Symbol const uniqueSymbol = Symbol() when used as property value in an object literal is inferred as unique type typeof uniqueSymbol.

Actual behavior:

Symbol const uniqueSymbol = Symbol() when used as property value in an object literal is inferred as general type symbol.

Related Issues:

Code

const uniqueSymbol = Symbol()

// Example of incorrect inference (unique symbol is generalized to type `symbol`)

const foo = {
  prop: uniqueSymbol,
}

type Foo = typeof foo  // { prop: symbol }

// Workarounds for incorrect behavior

const bar = {
  prop: uniqueSymbol as typeof uniqueSymbol,
}

type Bar = typeof bar // { prop: typeof uniqueSymbol }

const genericFactory = <T>(value: T) => ({ prop: value })

const baz = genericFactory(uniqueSymbol)

type Baz = typeof baz // { prop: typeof uniqueSymbol }

Output

"use strict";
const uniqueSymbol = Symbol();
// Example of incorrect inference (unique symbol is generalized to type `symbol`)
const foo = {
    prop: uniqueSymbol,
};
// Workarounds for incorrect behavior
const bar = {
    prop: uniqueSymbol,
};
const genericFactory = (value) => ({ prop: value });
const baz = genericFactory(uniqueSymbol);

Compiler Options

{
  "compilerOptions": {
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "strictPropertyInitialization": true,
    "strictBindCallApply": true,
    "noImplicitThis": true,
    "noImplicitReturns": true,
    "useDefineForClassFields": false,
    "alwaysStrict": true,
    "allowUnreachableCode": false,
    "allowUnusedLabels": false,
    "downlevelIteration": false,
    "noEmitHelpers": false,
    "noLib": false,
    "noStrictGenericChecks": false,
    "noUnusedLocals": false,
    "noUnusedParameters": false,
    "esModuleInterop": true,
    "preserveConstEnums": false,
    "removeComments": false,
    "skipLibCheck": false,
    "checkJs": false,
    "allowJs": false,
    "declaration": true,
    "experimentalDecorators": false,
    "emitDecoratorMetadata": false,
    "target": "ES2017",
    "module": "ESNext"
  }
}

Playground Link: Provided

Symbol type is incorrectly generalized when used as a property value of an object literal

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Symbol type is incorrectly generalized when used as a property value of an object literal

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Bắt đầu từ đâu

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