Fall-through in the last case of a switch statement

[DartBot]

This issue was originally filed by alexe.kaigorodov@gmail.com

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Spec "13.9 Switch" has follwing two assertions:

The last case in a switch (default or otherwise) can ‘fall-through’ to the end of the statement.
...
It is a static warning if the last statement of the statement sequence sk is not a
break, continue, return or throw statement.

To comply with the first assertion, the second assertion should be adjusted so that it does not apply to the last case in a switch.

Currently analyzer warns of "fall through" from the last case, which has no sense.

[anders-sandholm]

Please file an editor issue (or change Area) once this is fixed in the spec.

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Added Area-Language, Triaged labels.

[DartBot]

This comment was originally written by rodion...@unipro.ru

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Spec 0.20 changed this to a runtime error instead of a static warning, but
analyzer still reports one regardless of whether or not it's the last case

[DartBot]

This comment was originally written by rodion...@unipro.ru

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see co19 test Language/12_Statements/14_Continue_A02_t13

[kevmoo]

Not sure if this overlaps:

switch(truth) {
  case true:
    if(foo.contains(baz)) {
      return 0;
    } else {
      return 1;
    }
  default:
    throw 'silly, I know';
}

The last statement of the 'true' case is not a return, but the effect is to always return.

Could this be valid?

[bwilkerson]

The specification currently states:

It is a static warning if the last statement of the statement sequence sk is not a break, continue, return or throw statement.

This has a couple of problems (including the fact that 'throw' is an expression, not a statement, and that 'rethrow' isn't included in the list), not the least of which is that it disallows code patterns like the one Kevin included. Unfortunately, changing it to allow such code patterns would require specifying when statements and expressions are considered to terminate. I'm guessing that isn't likely to happen, but Gilad would know better than I.

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Set owner to @gbracha.