Change in type inference for `Object.entries()`

[printfn]

function foo(x?: object) {
    return Object.entries(x || {})
        .sort(([k1, v1], [k2, v2]) => v1.name.localeCompare(v2.name));
}

This passes typechecking in 5.8.3 but fails in b00279c. While tsc infers v1 and v2 as any, tsgo infers them as unknown.

tsconfig.json

{
	"compilerOptions": {
		"target": "ES2020",
		"useDefineForClassFields": true,
		"lib": ["esnext", "dom", "dom.iterable"],
		"module": "ESNext",
		"skipLibCheck": true,

		"moduleResolution": "Bundler",
		"allowImportingTsExtensions": true,
		"isolatedModules": true,
		"verbatimModuleSyntax": true,
		"moduleDetection": "force",
		"noEmit": true,
		"jsx": "react-jsx",
		"esModuleInterop": true,
		"allowJs": false,

		"strict": true,
		"forceConsistentCasingInFileNames": true,
		"noFallthroughCasesInSwitch": true,
		"sourceMap": false,
		"noImplicitAny": true,
		"checkJs": false,
		"strictBindCallApply": true,
		"strictFunctionTypes": true,
		"noImplicitThis": true,
		"alwaysStrict": true,
		"noUncheckedIndexedAccess": true,
		"useUnknownInCatchVariables": true,
		"strictNullChecks": true
	},
	"include": ["*.ts"]
}

[Andarist]

It's a type ordering issue again. A shorter repro is this:

function foo(x?: object) {
  const reduced = x || {}; // Strada: object; Corsa: {};
}

And the problem with {} and object is that they are mutually strict subtypes of each other. So depending on the order of the types a different type might get eliminated by removeSubtypes and thus a different result gets returned.

But then they don't quite behave the same way for the purpose of other relationship checks. So if this argument gets checked against the param type of the first overload instantiated candidate ({ [s: string]: unknown; } | ArrayLike<unknown>) we get different results:

type Target = { [s: string]: unknown; } | ArrayLike<unknown>
const a: Target = {} as {} // ok
const b: Target = {} as object // error

In other words, in Corsa that || reduced to {} and that made the first overload to be selected, while in Strada || is reduced to object here and the first overload can't be matched so it selects the second one.

[ahejlsberg]

Hmm, this seems like something we want to fix. In Strada, object always has a lower type ID than {} and other object types and is therefore always first in the union constituent sort order. We should ensure that is also the case in Corsa (specifically, we should ensure that object sorts before object types in the total type ordering). I'll put up a PR.