add type check to zirSwitchBlockErrUnion

[Rexicon226]

fixes #18592

[Rexicon226]

I know what I did wrong, one sec! 🤣

[dweiller]

Is it worth adding a compile error test in test/cases/compiler_errors?

[Rexicon226]

Is it worth adding a compile error test in test/cases/compiler_errors?

Ah, good point.

[Rexicon226]

I wonder if this is something that should error somewhere in the catch logic, instead of the switch already. Like in AstGen, if possible 🤔

[dweiller]

I don't think it can happen in astgen - the case in the issue could, but not something like:

const a = true;
a catch |e| switch (e) {
    // ...
};

[Rexicon226]

Yeah, you're right. Was just a thought.