RFR: 8343540: Report preview error for inherited effectively-preview methods [v2]

[Vicente Romero]

On Mon, 18 Nov 2024 11:47:07 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

>> Consider a case where a new preview interface is introduced to JDK, and an existing non-preview class is retrofitted to use it. I.e. a case like:
>> 
>> 
>> //JDK types:
>> @PreviewFeature(...)
>> public interface NewAPI {
>>     public default void test() {}
>> }
>> public class ExistingRetrofittedClass implements NewAPI {}
>> 
>> //user type:
>> class Test {
>>     void t(ExistingRetrofittedClass c) {
>>         c.test();
>>     }
>> }
>> 
>> 
>> There is currently no error or warning about the invocation of the test method, as the method itself is not marked as preview, and the receiver is not preview either.
>> 
>> The proposal herein is that invoking a method on a receiver that is not of preview type itself, but the method is declared in a preview class or interface, the method will be considered to be a preview method, and the appropriate error or warning will be printed. Similar behavior is implementing for dereferencing fields.
>> 
>> 
>> Similarly when implementing or overriding such "effectively" preview methods, like:
>> 
>> 
>> //user types:
>> class Test1 extends ExistingRetrofittedClass {
>>     public void test() {}
>> }
>> 
>> 
>> java also does not produce any error or warning. If the method itself would be marked as preview, an error or warning would be printed.
>> 
>> The proposal herein is to produce an error or warning for a method declared inside a non-preview class or interface, which directly overrides a method declared inside a preview class or interface.
>> 
>> In particular, for the two example above, javac is currently producing no errors. With the change proposed herein, javac will produce output like (with no `--enable-preview`):
>> 
>> 
>> src/Test1.java:4: error: test() is a preview API and is disabled by default.
>>     public void test() {}
>>                 ^
>>   (use --enable-preview to enable preview APIs)
>> src/Test.java:5: error: test() is a preview API and is disabled by default.
>>         c.test();
>>          ^
>>   (use --enable-preview to enable preview APIs)
>> 2 errors
>
> Jan Lahoda has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Adding tests.

lgtm

-------------

Marked as reviewed by vromero (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/21953#pullrequestreview-2452019520