Switch Expression - complete normally - spec omission?

[Gavin Bierman]

Thanks Manoj. I’ve filed this as a bug [1] and we’ll fix it for JDK 15. 

Cheers,
Gavin

[1] https://bugs.openjdk.java.net/browse/JDK-8245546 <https://bugs.openjdk.java.net/browse/JDK-8245546> 

> On 16 May 2020, at 10:10, Manoj Palat <manoj.palat at in.ibm.com> wrote:
> 
> Thanks Alex for the reply and clarifying that we are discussing Switch Statements with Switch rules.
> My bad for putting the title as Switch Expressions - don't want to correct the title now which
> will break the chain of the mail.
> 
> Regards,
> Manoj
> 
> -----"amber-spec-experts" <amber-spec-experts-bounces at openjdk.java.net> wrote: -----
> To: amber-spec-experts at openjdk.java.net
> From: Alex Buckley
> Sent by: "amber-spec-experts"
> Date: 05/15/2020 11:34PM
> Subject: [EXTERNAL] Re: Switch Expression - complete normally - spec omission?
> 
> On 5/14/2020 7:22 PM, Manoj Palat wrote:
>> I think there is a spec omission regarding "complete normally for switch statements whose switch block consists of switch rules
>> 
>> Ref JLS 14 Sec 14.22
>> ...
>> A switch statement whose switch block consists of switch rules can complete
>> normally iff at least one of the following is true:
>> – One of the switch rules introduces a switch rule expression (which is
>> necessarily a statement expression).
>> – One of the switch rules introduces a switch rule block that can complete
>> normally.
>> – One of the switch rules introduces a switch rule block that contains a reachable
>> break statement which exits the switch statement.
>> ...
>> Now consider:
>> 
>> switch (b) {
>> case 1 -> {
>> throw new Exception();
>> }
>> }
>> 
>> As per the above definition, this switch statement cannot complete normally;
>> but consider "b" having a value other than 1 and then it completes normally.
> 
> /* -----
> To demonstrate the point, the switch statement above uses a switch rule
> block that completes abruptly, but could alternatively have used a
> switch rule `throw` statement:
> 
> switch (b) {
>   case 1 -> throw new Exception();
> }
> 
> Also, to clarify for the many readers of this list, we are discussing
> switch statements, which never require a `default` label. We are not
> discussing switch expressions, which almost always require a `default`
> label.
> ----- */
> 
>> 
>> Also consider, 14.11.3. which says:
>> "If no switch label matches, the entire switch statement completes normally."
>> 
>> which looks inconsistent. One hand says: "completes normally" the other:
>> "iff at least one of the following ..." not mentioning default.
>> 
>> Hence, shouldn't the item,
>> -> – The switch block does not contain a default label.
>> 
>> also be added in the list in 14.22?
> 
> I agree that without a `default` switch label, 14.11.3 may evaluate "If
> no switch label matches, the entire switch statement completes
> normally."  Since we can see a way for the statement to complete
> normally, 14.22 ought to say that the statement _can_ complete normally.
> So, it looks right to add "– The switch block does not contain a default
> label."
> 
> Alex
> 
> 

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