multi return type declaration emit not as expected

TypeScript Version: 3.8.0-dev.20191213

Search Terms:

Code

origin code

export const enum EnumParseInputUrl
{
	UNKNOWN,
	STRING,
	URL,
	URLSEARCHPARAMS,
}

export function parseInputUrl<T extends string | number | URL | URLSearchParams>(_input: T)
{
	if (typeof _input === 'number')
	{
		let value = _input.toString();

		return {
			type: EnumParseInputUrl.STRING,
			_input,
			value,
		}
	}
	else if (typeof _input === 'string')
	{
		let value = _input.toString();

		return {
			type: EnumParseInputUrl.STRING,
			_input,
			value,
		}
	}
	else if (_input instanceof URL)
	{
		let value = _input;

		return {
			type: EnumParseInputUrl.URL,
			_input,
			value,
		}
	}
	else if (_input instanceof URLSearchParams)
	{
		let value = _input;

		return {
			type: EnumParseInputUrl.URLSEARCHPARAMS,
			_input,
			value,
		}
	}

	let value = _input.toString();

	return {
		type: EnumParseInputUrl.UNKNOWN,
		_input,
		value,
	}
}

the code of if i want export as expected

export function parseInputUrl<T extends string | number | URL | URLSearchParams>(_input: T)
{
	if (typeof _input === 'number')
	{
		let value = _input.toString();

		return {
			type: EnumParseInputUrl.STRING as const,
			_input,
			value,
		}
	}
	else if (typeof _input === 'string')
	{
		let value = _input.toString();

		return {
			type: EnumParseInputUrl.STRING as const,
			_input,
			value,
		}
	}
	else if (_input instanceof URL)
	{
		let value = _input;

		return {
			type: EnumParseInputUrl.URL as const,
			_input,
			value,
		}
	}
	else if (_input instanceof URLSearchParams)
	{
		let value = _input;

		return {
			type: EnumParseInputUrl.URLSEARCHPARAMS as const,
			_input,
			value,
		}
	}

	let value = _input.toString();

	return {
		type: EnumParseInputUrl.UNKNOWN as const,
		_input,
		value,
	}
}

Expected behavior:

export declare function parseInputUrl<T extends string | number | URL | URLSearchParams>(_input: T): {
    type: EnumParseInputUrl.STRING;
    _input: T & number;
    value: string;
} | {
    type: EnumParseInputUrl.STRING;
    _input: T & string;
    value: string;
} | {
    type: EnumParseInputUrl.URL;
    _input: T & URL;
    value: T & URL;
} | {
    type: EnumParseInputUrl.URLSEARCHPARAMS;
    _input: T & URLSearchParams;
    value: T & URLSearchParams;
} | {
    type: EnumParseInputUrl.UNKNOWN;
    _input: T;
    value: string;
};

Actual behavior:

export declare const enum EnumParseInputUrl {
    UNKNOWN = 0,
    STRING = 1,
    URL = 2,
    URLSEARCHPARAMS = 3
}
export declare function parseInputUrl<T extends string | number | URL | URLSearchParams>(_input: T): {
    type: EnumParseInputUrl;
    _input: T & URL;
    value: T & URL;
} | {
    type: EnumParseInputUrl;
    _input: T & URLSearchParams;
    value: T & URLSearchParams;
} | {
    type: EnumParseInputUrl;
    _input: T;
    value: string;
};

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Related Issues:

Start by compiling the supplied TypeScript reproduction with declaration emit using the reported 3.8.0-dev.20191213 version and compare the actual declaration with the expected output. Trace the compiler path responsible for inferring and emitting the function's return type; done means the emitted declaration preserves the distinct enum members and narrowed intersections shown in the expected behavior.