RFR: JDK-8207224: Javac compiles source code despite illegal use of unchecked conversions
joe darcy
joe.darcy at oracle.com
Mon Dec 3 18:50:27 UTC 2018
Hi Vicente,
Since it sounds like there is nontrivial source compatibility impact
with this change, please file a CSR for it.
Thanks,
-Joe
On 12/2/2018 6:24 PM, Vicente Romero wrote:
> Hi Liam,
>
> Thanks for testing the change. Yes the change you found is an expected
> result of the fix. If the number of rejected examples is not big I
> think that we could go on with the fix. Eclipse compiler should be
> rejecting that code too.
>
> Vicente
>
> On 12/2/18 4:01 PM, Liam Miller-Cushon wrote:
>> Hi Vicente,
>>
>> I did some testing with your fix to get a sense of the source
>> compatibility impact, and it looks minor: I only found a handful of
>> examples that are rejected after the change.
>>
>> One of them is in icu4j. Is this change an expected result of the fix?
>>
>> icu/icu4j/main/classes/core/src/com/ibm/icu/impl/locale/XLikelySubtags.java:47:
>> error: make() in <anonymous
>> com.ibm.icu.impl.locale.XLikelySubtags$Maker$1> cannot override
>> <V>make() in Maker
>> public Map<Object,Object> make() {
>> ^
>> return type Map<Object,Object> is not compatible with V
>> where V is a type-variable:
>> V extends Object declared in method <V>make()
>> ...
>> https://github.com/unicode-org/icu/blob/master/icu4j/main/classes/core/src/com/ibm/icu/impl/locale/XLikelySubtags.java#L47
>>
>> Thanks,
>>
>> On Sat, Dec 1, 2018 at 11:47 AM Vicente Romero
>> <vicente.romero at oracle.com <mailto:vicente.romero at oracle.com>> wrote:
>>
>> Please review fix for [1] at [2]. Javac is accepting this program
>> as valid:
>>
>> class ReturnTypeSubstitutableTest {
>> abstract class AbstractDemo<Request extends AbstractResult,
>> Response extends AbstractResult> {
>> protected abstract Response test(Request request);
>> }
>>
>> abstract interface AbstractResult {}
>>
>> abstract interface SimpleResult extends AbstractResult {}
>>
>> class Result1 implements SimpleResult {}
>>
>> class OtherResult implements AbstractResult {}
>>
>> public class SimpleDemo<Request extends AbstractResult,
>> Response extends AbstractResult> extends AbstractDemo<Request,
>> Response> {
>> @Override
>> protected SimpleResult test(AbstractResult request)
>> {<----------- this method is accepted as a good override for
>> AbstractDemo::test
>> return null;
>> }
>> }
>> }
>>
>> From Dan's evaluation at the bug entry [1]:
>>
>> Per JLS 8.4.8.3, the first method must be
>> return-type-substitutable for the second. This can be satisfied
>> in 3 ways (JLS 8.4.5):
>> - SimpleResult is a subtype of Response (no)
>> - SimpleResult can be converted to a subtype of Response by
>> unchecked conversion (no)
>> - The methods have different signatures (yep) and SimpleResult =
>> erasure(Response) (no)
>>
>> No case applies, so an error should occur. This fix syncs javac
>> with the spec.
>>
>> Thanks,
>> Vicente
>>
>> [1] https://bugs.openjdk.java.net/browse/JDK-8207224
>> [2] http://cr.openjdk.java.net/~vromero/8207224/webrev.00/
>> <http://cr.openjdk.java.net/%7Evromero/8207224/webrev.00/>
>>
>
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