[bazoom42]

The “as” expression is not valid JavaScript anyway, so the default rule for implicit semicolon does not apply. A grammer for type expressions could define if and how semicolons should be inserted.

[zarzavat]

TypeScript already has such type operators though. For example:

    type T = keyof
    {
      a: null,
      b: null
    }

Here T is “a”|”b”, no automatic semicolon is inserted after `keyof`. While I don’t personally write code like this, I’m sure that someone does. It’s perfectly within the rules, after all.

While it’s true that TS doesn’t have to follow JS rules for semicolon insertion in type expressions, it always has done, and probably always should do.

[bazoom42]

This is just the default. Automatic semicolon insertion only happen in specific well-defined cases, for example after the “return” keyword or when an invalid expression can be made valid by semicolon insertion. Neither applies here.