RFR: 8357016: Candidate main methods not computed properly

[Jaikiran Pai]

On Thu, 15 May 2025 16:42:48 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

> A consider class like this:
> 
> 
> public class TwoMains {
>     private static void main(String... args) {}
>     static void main() {
>         System.out.println("Should be called, but is not.");
>     }
> }
> 
> 
> The `MethodFinder` will do lookup for the `main(String[])` method, and it finds one, so does not proceed with a lookup for `main()`. But then, it will check the access modifier, and will reject that method, never going back to the `main()` method. This is not what the JLS says about the lookup - the private method is not a candidate, and should be ignored.
> 
> Something similar happens if the return type is not `void`.
> 
> This PR is fixing that by checking whether the `main(String[])` method is usable early, and falling back to `main()` if it `main(String[])` is not usable.
> 
> It also removes the check for the `abstract` method, as that, by itself, is not really backed by JLS, but adds a check for `abstract` class, producing a user-friendly message is trying to invoke an instance `main` method on an `abstract` class (which, obviously, cannot be instantiated).

test/jdk/tools/launcher/Arrrghs.java line 607:

> 605:         //private method with parameter, usable method without parameter:
> 606:         createJar(new File("some.jar"), new File("Foo"),
> 607:             "private static void main(String[] args){}",

Perhaps we should even include a instance method `private void main(String[] args) {}` to cover that case?

test/jdk/tools/launcher/Arrrghs.java line 635:

> 633:         tr.contains("Error: abstract class Foo can not instantiated");
> 634:         if (!tr.testStatus)
> 635:             System.out.println(tr);

Hello Jan, I think this is pre-existing, but it looks like we don't fail the test even when `tr.testStatus` indicates a failure? We seem to only write out to `System.out` and return from the test method. Am I misreading the test code?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25256#discussion_r2092758973
PR Review Comment: https://git.openjdk.org/jdk/pull/25256#discussion_r2092755321