Typescript: Incorrect error message with String Literal Types

[llwwbb]

TypeScript Version: 3.6.0-dev.20190730

Search Terms:
String Literal Types

Code

type ACT = 'submit';
interface Test {
    histories: {
        act: ACT,
        time: number,
    }[],
}
function test(o: Test){

}
test({histories: [{act: 'submit'}]})

Expected behavior:
Property 'time' is missing in type '{ act: ACT; }' but required in type '{ act: ACT; time: number; }'.

Actual behavior:
Type 'string' is not assignable to type '"submit"'.

Playground Link:

Related Issues:

[IllusionMH]

You should use as const to tell compiler that string 'submit' shouldn't be widened to string

Example: http://www.typescriptlang.org/play/index.html#code/C4TwDgpgBAggwgFSgXigcgM4FcBGBbAS2DQG4BYAKAIDtgIAnAMwEMBjaBCDYKAb0qiCoACwLcA9vQJcAXHwFDFbYHPgIANAsWDgBPBDnUseHA00VFAXwDaAXXOXKjLNVa7x1KHW4AKcXM5uAEp+CkpHCm9gH15RCSlZKGteZTlMXEJiKGYMKFYPbktbSyCgA

[nmain]

You should use as const to tell compiler that string 'submit' shouldn't be widened to string

Yes, but the contextual type handles that here if time is specified, so I think that this is surprising.

http://www.typescriptlang.org/play/index.html#code/C4TwDgpgBAggwgFSgXigcgM4FcBGBbAS2DQG4BYAKAIDtgIAnAMwEMBjaBCDYKAb0qiCoACwLcA9vQJcAXHwFDFbYHPgIANAsWDgBPBDnUseHA00VFAXwDaAXXOXKjLNVa7x1KHW4AKcXM5uAEp+CkpHCm9gH15RCSlZKGteZTlMXEJidS89AygAZihLW0sgoA

[llwwbb]

It seems that this issue has been fixed in version 3.9.2