Compiler gives wrong error message when matching on invalid enum value

[orenbenkiki]

Trying to compile the following code:

enum Foo { Bar, Baz }
fn bug(foo: Foo) {
    match (foo, foo) {
      (Bar, Bar) => {},
      (Bar, Bug) => {},
      (Bar, Baz) => {},
    }
}

I get the error message:

..........:6:6: 6:16 error: unreachable pattern
..........:6       (Bar, Baz) => {},
                   ^~~~~~~~~~

Instead of an error message complaining that Bug isn't a valid value for the matched enum (in fact, it isn't even defined anywhere). The error message doesn't even point at the line containing the bad value - it took me a while to figure out what was going on.

[huonw]

This is because the compiler takes (Bar, Bug) to be creating a new variable Bug bound to the second field of the tuple, i.e. same as (Bar, a). I'm inclined to close this as a dupe of #10304.

[huonw]

Hm, #10402 is also similar, so I think this is covered by the combination of those two. Closing.