Multiple issues with template literal type narrowing and relations

[ahejlsberg]

🕗 Version & Regression Information

Every version.

⏯ Playground Link

Playground link with relevant code

💻 Code

function f1(x: `foo-${string}`, y: `${string}-bar`) {
    if (x === y) {  // Wrongly reports error that types don't overlap (they do, e.g. 'foo-xxx-bar')
    }
}

function f2(x: string, y: `foo-${string}` | 'bar') {
    if (x === y) {
        x;  // Narrowed to 'bar', should be `foo-${string}` | 'bar'
    }
}

function f3(x: string, y: `foo-${string}`) {
    if (x === 'foo-test') {
        x;  // Narrowed to 'foo-test'
    }
    if (y === 'foo-test') {
        y;  // Not narrowed but should be
    }
}

🙁 Actual behavior

See above.

🙂 Expected behavior

See above.

[craigphicks]

That was very kind of you to attempt to classify fixed prefixes - and fixed mid?/post-fixes too. I would have thought that classifying fixed prefixes alone would be sufficient.