Introduce ability to recognize and execute user main method(s)

[dmlloyd]

Description
Introduce ability to recognize and execute user main method(s).

Requirements

• Introduce a means to identify a method as a main method (e.g. an annotation)
• Allow build-time configuration to specify which main method (if any) should be used for the build (can @Named be used for this?)
• The main method should be allowed to optionally accept a String[] or List<String> which contains the command arguments (minus the arguments processed by Introduce config-based command line argument binding #6497)
• The main method should be allowed to optionally return an int which contains the desired exit code
• If the application shutdown fails with an exception, there should be a means to override the exit code.
• A mechanism may be defined to allow users to customize the mapping of exception to exit code; if implemented, the mechanism should accept the exception and the originally requested exit code, and return the new exit code. If the mapping fails with an exception, an exit code of 1 should be used.
• System.exit() should be called with the final exit code once all shutdown work is complete (at the end of the launcher main method).
• If no main method is defined, then the waitForExit method defined in Introduce an exit request API with wait-for-exit method #6498 should be used, with the code returned from that method being used as the requested exit code

Exit codes reference

Code	Description
0	Normal exit (no error, clean shutdown)
1	Exit due to uncaught exception
2	Exit due to configuration or usage error
10	(reserved due to its usage with JBoss)

[maxandersen]

Reading the proposed items I'm struggling to figure out if I'll be able to as follows:

class Main {
public static void main(String... args) {
    QuarkusApplication.start(Main::handler, args); 
} 

int handler(String... args) {
   ...
}
}

here I'm just using a method reference, but could also be a class.

Main point is that I'll have a plain static main that can be booted by Quarkus.

Or is the expectation all is always handled by Quarkus ?

[dmlloyd]

That seems doable to me. We just have to be sure that the Quarkus build process has a way to know which entry point main to use during build.

[maxandersen]

Yes, I assume we'll have a way to do both - the explicit main() method is mainly just for easy launching from IDE or command line jar runs.

[dodalovic]

@maxandersen Just curious how far we are from this wonderful feature?
Cheers

[maxandersen]

@dodalovic sorry - didn't see your ping here before now - see #7681 for current progress

[maxandersen]

@stuartwdouglas how much of this is fullfilled by #7681 ?

[stuartwdouglas]

Most of it, except for exception mapping for exit codes, which is going to be a follow up. Also failure due to config issue does not have it's own exit code, however that can be done as part of the exception mapping work.