The introduction of Sequenced collections is not a source compatible change

[Stuart Marks]

Hi Rémi,

Thanks for trying out the latest build!

I'll make sure this gets mentioned in the release note for Sequenced Collections. 
We'll also raise this issue when we talk about this feature in the Quality Outreach 
program.

s'marks

On 4/29/23 3:46 AM, Remi Forax wrote:
> I've several repositories that now fails to compile with the latest jdk21, which introduces sequence collections.
> 
> The introduction of a common supertype to existing collections is *not* a source compatible change because of type inference.
> 
> Here is a simplified example:
> 
>    public static void m(List<Supplier<? extends Map<String, String>>> factories) {
>    }
> 
>    public static void main(String[] args) {
>      Supplier<LinkedHashMap<String,String>> supplier1 = LinkedHashMap::new;
>      Supplier<SortedMap<String,String>> supplier2 = TreeMap::new;
>      var factories = List.of(supplier1, supplier2);
>      m(factories);
>    }
> 
> 
> This example compiles fine with Java 20 but report an error with Java 21:
>    SequencedCollectionBug.java:28: error: method m in class SequencedCollectionBug cannot be applied to given types;
>      m(factories);
>      ^
>    required: List<Supplier<? extends Map<String,String>>>
>    found:    List<Supplier<? extends SequencedMap<String,String>>>
>    reason: argument mismatch; List<Supplier<? extends SequencedMap<String,String>>> cannot be converted to List<Supplier<? extends Map<String,String>>>
> 
> 
> 
> Apart from the example above, most of the failures I see are in the unit tests provided to the students, because we are using a lot of 'var' in them so they work whatever the name of the types chosen by the students.
> 
> Discussing with a colleague, we also believe that this bug is not limited to Java, existing Kotlin codes will also fail to compile due to this bug.
> 
> Regards,
> Rémi