A few comments on the general compatibility policy for the JDK.
Compatibility is looked after by the Compatibility and Specification
Review (CSR) process ( Compatibility & Specification Review).
Summarizing the approach,
The general compatibility policy for exported APIs implemented in the
JDK is:
* Don't break binary compatibility (as defined in the Java
Language Specification) without sufficient cause.
* Avoid introducing source incompatibilities.
* Manage behavioral compatibility changes.
https://wiki.openjdk.org/display/csr/Main
None of binary, source, and behavioral compatibly are absolutes and
judgement is used to assess the cost/benefits of changes. For example,
strict source compatibility would preclude, say, introducing new public
types in the java.lang package since the implicit import of types in
java.lang could conflict with a same-named type *-imported from another
package.
When a proposed change is estimated to be sufficiently disruptive, we
conduct a corpus experiment to evaluate the impact on the change on many
public Java libraries. Back in Project Coin in JDK 7, that basic
approach was used to help quantify various language design choices and
the infrastructure to run such experiments has been built-out in the
subsequent releases.
HTH,
-Joe
CSR Group Lead
On 5/4/2023 6:32 AM, Ethan McCue wrote:
I guess this a good time to ask, ignoring the benefit part of a cost
benefit analysis, what mechanisms do we have to measure the number of
codebases relying on type inference this will break?
Iirc Adoptium built/ran the unit tests of a bunch of public repos, but
it's also a bit shocking if the jtreg suite had nothing for this.
On Thu, May 4, 2023, 9:27 AM Raffaello Giulietti
<raffaello.giulie...@oracle.com> wrote:
Without changing the semantics at all, you could also write
final List<Collection<String>> list =
Stream.<Collection<String>>of(nestedDequeue, nestedList).toList();
to "help" type inference.
On 2023-05-03 15:12, fo...@univ-mlv.fr wrote:
> Another example sent to me by a fellow French guy,
>
> final Deque<String> nestedDequeue = new ArrayDeque<>();
> nestedDequeue.addFirst("C");
> nestedDequeue.addFirst("B");
> nestedDequeue.addFirst("A");
>
> final List<String> nestedList = new ArrayList<>();
> nestedList.add("D");
> nestedList.add("E");
> nestedList.add("F");
>
> final List<Collection<String>> list =
Stream.of(nestedDequeue, nestedList).toList();
>
> This one is cool because no 'var' is involved and using
collect(Collectors.toList()) instead of toList() solves the
inference problem.
>
> Rémi
>
> ----- Original Message -----
>> From: "Stuart Marks" <stuart.ma...@oracle.com>
>> To: "Remi Forax" <fo...@univ-mlv.fr>
>> Cc: "core-libs-dev" <core-libs-...@openjdk.java.net>
>> Sent: Tuesday, May 2, 2023 2:44:28 AM
>> Subject: Re: The introduction of Sequenced collections is not a
source compatible change
>
>> 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
