Allow "rethrow" to end a switch case

[munificent]

Here's a goofy corner of the language:

try {
  ...
} catch (err) {
  switch (err) {
    case 1:
      rethrow;
    case 2:
      print("Another case.");
  }
}

Analyzer reports:

[error] The last statement of the 'case' should be 'break', 'continue', 'return' or 'throw'. (...temp.dart, line 20, col 7)

This is correct. The spec does not mention allow rethrow to end a clause. It probably should?

[bwilkerson]

See also #21822

[lrhn]

The current specification is too restrictive to be really helpful.
It doesn't have a proper analysis, and without that kind of intelligence behind the warnings, they do occasionally look pretty stupid. Giving warnings that the user can clearly see are wrong is not being helpful.

Personally, I would just remove the warning and the throw at the end of switch cases, and just break the switch when a case's statements end. Simpler for everybody, except those that expect fall-through, they won't get any warnings.

[floitschG]

In the long term I agree with Lasse.
However, it seems like a very easy fix to just add rethrow to the list of accepted switch breaks.

[kmillikin]

Also see #7537

[munificent]

This is fixed in the spec, but have the implementations implemented it? Have we documented it? Written tests?

[lrhn]

It's also fixed in the analyzer (1322877). Since this is entirely a warning issue, that's the extend of the implementation.

There is a test (1d4657f).

As for documentation, it is in the spec, and it is (now) in the CHANGELOG.md (be4b4c6)

It seems dart2js doesn't check anyway, so I ignored it.

[munificent]

it is (now) in the CHANGELOG.md (be4b4c6)

Groovy, thanks!