RFR: 8344706: Compiler Implementation of Compact Source Files and Instance Main Methods [v4]

[Jan Lahoda]

On Tue, 22 Apr 2025 10:14:44 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

>> src/java.base/share/classes/jdk/internal/misc/MethodFinder.java line 89:
>> 
>>> 87:         if (mainMethod == null) {
>>> 88:             //if not public method, try to lookup a non-public one
>>> 89:             mainMethod = JLA.findMethod(cls, false, "main", String[].class);
>> 
>> Is there a reason why the first findMethod can't use publicOnly=false?
>
> My reason was that when `publicOnly=false`, there's more classloading happening (unsurprisingly, as also the non-public methods must be resolved). Which may lead to a change of behavior if the traditional `public static main(String[])` exists.
> 
> IIRC there is a test relying on this behavior, but I don't have the name offhand. Will put it here when I have it.
> 
> For example:
> 
> $ cat Main.java 
> public class Main {
>     public static void main(String... args) {
>         System.err.println("Hello!");
>     }
>     private Missing get() { return null; }
> }
> $ cat Missing.java 
> public class Missing {
> }
> $ jdk-24/bin/javac Main.java Missing.java; rm Missing.class
> $ jdk-24/bin/java -classpath . Main
> Hello!
> $ jdk-without-publicOnly=true/bin/java -classpath . Main
> Error: Unable to initialize main class Main
> Caused by: java.lang.NoClassDefFoundError: Missing

The tests that would be affected by the extra classloading appear to be:

test/jdk/java/lang/System/SecurityManagerWarnings.java
test/jdk/java/lang/System/LoggerFinder/SignedLoggerFinderTest/SignedLoggerFinderTest.java

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PR Review Comment: https://git.openjdk.org/jdk/pull/24438#discussion_r2056303456