infer type fail when type is ([k1, t1] | [k2, t2])[] like

[bluelovers]

TypeScript Version: Version 3.8.0-dev.20200123

Search Terms:

Code

export type IEntrie = (
	['a', string]
	| ['b', string]
	| ['c', string]
	| ['d', string]
	| ['e', number]
	)

export default (Object.entries({}) as IEntrie[])
.map(([siteID, table]) => {

	if (siteID === 'e')
	{

		console.dir(siteID) // infer should is 'e
		console.dir(table + 0) // infer should is number

		return {
			siteID,
			table,
		}
	}
	else
	{
		console.dir(siteID) // infer should is a b c d
		console.dir(table) // infer should is string

		return {
			siteID,
			table,
		}
	}
})

Expected behavior:

when siteID is e, table should is number, not string | number
when siteID is not e, table should is string, not string | number

export declare type IEntrie = (['a', string] | ['b', string] | ['c', string] | ['d', string] | ['e', number]);
declare const _default: ({
    siteID: "e";
    table: number;
} | {
    siteID: "a" | "b" | "c" | "d";
    table: string;
})[];
export default _default;

Actual behavior:

Error:(20, 15) TS2365: Operator '+' cannot be applied to types 'string | number' and 'number'.

export declare type IEntrie = (['a', string] | ['b', string] | ['c', string] | ['d', string] | ['e', number]);
declare const _default: ({
    siteID: "e";
    table: string | number;
} | {
    siteID: "a" | "b" | "c" | "d";
    table: string | number;
})[];
export default _default;

Playground Link:

Related Issues:

[nmain100]

Duplicate of #32639 which is a duplicate of #12184. My search terms were "dependent narrowing".

Everything works as expected if you don't destructure into [siteID, table], but once you do you have two separate variables and Typescript doesn't track the relation between narrowing one causing a narrowing of the other.