[jdk16] RFR: 8213032: program fails with LambdaConversionException at execution time

Vicente Romero vromero at openjdk.java.net
Thu Dec 17 23:47:05 UTC 2020


Currently javac is accepting this code:

import java.util.stream.*;

public class Test {
    interface I {}
    static abstract class C { }
    static class A extends C implements I { }
    static class B extends C implements I { }

    static String f(I i) { return null; }

    public static void main(String[] args) {
        Stream.of(new A(), new B()).map(Test::f).forEach(System.out::println);

the line with the method reference can also be written using a lambda expression like in:

        Stream.of(new A(), new B()).map(i -> f(i)).forEach(System.out::println);
but the code with the method reference, is failing later at execution time with `LambdaConversionException`. Currently javac is desugaring the method reference to the equivalent lambda but the argument of generated lambda is: `Test$I` at the same time the target type of the method reference has argument with type `C & I` which will be desugared by the compiler to `C`. This is the reason for the runtime error. The right type for the argument of the desugared method generated by javac is `C` which is what this patch is doing. The change to method `ReferenceTranslationContext::bridgedRefSig` has been done in order to obtain a more exact version of the target type, as the current implementation is returning `Object` in most cases, which is OK, but I think that we could generate a better, more accurate, type.

TIA for the review


Commit messages:
 - 8213032: program fails with LambdaConversionException at execution time

Changes: https://git.openjdk.java.net/jdk16/pull/49/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk16&pr=49&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8213032
  Stats: 61 lines in 2 files changed: 54 ins; 4 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk16/pull/49.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk16 pull/49/head:pull/49

PR: https://git.openjdk.java.net/jdk16/pull/49

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