"Cannot resolve symbol al" after `else if (! (l instanceof ArrayList al))`

[David Alayachew]

This definitely looks like a bug. Maybe some of the amber folks are busy
with Valhalla or something, but I can't see this NOT being a bug.

@Angelos Bimpoudis <angelos.bimpoudis at oracle.com> poke poke poke

On Sat, Jun 7, 2025, 3:14 AM Jean-Noël Rouvignac <
jean-noel.rouvignac at pingidentity.com> wrote:

> Hello folks,
>
> JDK 25 rampdown phase 1 is now behind us, congrats and thanks for all the
> work done to get there!
>
> I am reviving this use case to see if anyone agrees that this may be a bug?
>
> Thank you,
> Jean-Noel
>
>
> On Wed, Apr 16, 2025 at 11:37 AM Jean-Noël Rouvignac <
> jean-noel.rouvignac at pingidentity.com> wrote:
>
>> Hello amber-dev folks!
>>
>> While using pattern matching for instanceof I noticed a small incoherent
>> oddity.
>>
>> Take this code:
>> ```
>> static void ensureCapacity(List l) {
>>   if (l instanceof LinkedList) {
>>     throw new IllegalArgumentException("Use an efficient list
>> implementation");
>>   } else if (!(l instanceof ArrayList al)) {
>>     return;
>>   }
>>   al.ensureCapacity(10);
>>   System.out.println("done");
>> }
>>
>> ensureCapacity(new ArrayList());
>> ```
>>
>> The compiler rejects this code with: `Cannot resolve symbol 'al'`.
>> (I have tested that code with JDK 24 in the playground (
>> https://dev.java/playground) but also in my IDE with JDK 21)
>>
>> However #1, removing the `else` keyword makes the code successfully
>> compile:
>> ```
>>   }
>>   if (!(l instanceof ArrayList al)) {
>>     return;
>>   }
>> ```
>>
>> However #2, adding an additional `else` keyword makes the code
>> successfully compile:
>> ```
>>         } else if (!(l instanceof ArrayList al)) {
>>             return;
>>         } else {
>>             al.ensureCapacity(10);
>>             System.out.println("done");
>>         }
>> ```
>>
>> While option #1 and #2 are acceptable workarounds, it looks to me like
>> there could be a bug in javac? Therefore I am bringing this to your
>> attention so you can decide if it is a bug or not.
>>
>> I searched the JDK's bug tracker for this specific case, but could not
>> find anything related.
>>
>> Thanks!
>> Jean-Noël
>>
>
>
> --
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> Jean-Noel Rouvignac
> Senior Principal Software Engineer
> jean-noel.rouvignac at pingidentity.com
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