JDTLanguageServer cannot run well without IApplication

[mickaelistria]

While trying to run the language server via code (in a Java process, as part of an Eclipse IDE plugin), it looks like the only vaid entry-point is the LanguageServer implements IApplication. However, this one does force to use some streams accoridng to application execution context.
If one tries to bypass it, directly calling the JDTLanguageServer, there are some issues later on as the execution flow of the language server goes through the JavaLanguageServerPlugin to access some fields, which are only set (and settable) from the LanguageServer/IApplication; so another client cannot set those fields.
The JavaLanguageServerPlugin should allow to have those fields set, or JDT-LS should provide a dedicated launcher that would allow to use any stream (typically some java.nio.channels.Pipe ) and that would set up all the necessary state.

Here is the error I get

java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
	at org.eclipse.lsp4j.jsonrpc.services.GenericEndpoint.lambda$null$0(GenericEndpoint.java:67)
	at org.eclipse.lsp4j.jsonrpc.services.GenericEndpoint.request(GenericEndpoint.java:120)
	at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.handleRequest(RemoteEndpoint.java:261)
	at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.consume(RemoteEndpoint.java:190)
	at org.eclipse.lsp4j.jsonrpc.json.StreamMessageProducer.handleMessage(StreamMessageProducer.java:194)
	at org.eclipse.lsp4j.jsonrpc.json.StreamMessageProducer.listen(StreamMessageProducer.java:94)
	at org.eclipse.lsp4j.jsonrpc.json.ConcurrentMessageProcessor.run(ConcurrentMessageProcessor.java:113)
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:539)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
	at java.base/java.lang.Thread.run(Thread.java:833)
Caused by: java.lang.reflect.InvocationTargetException
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:568)
	at org.eclipse.lsp4j.jsonrpc.services.GenericEndpoint.lambda$null$0(GenericEndpoint.java:65)
	... 11 more
Caused by: java.lang.NullPointerException: Cannot invoke "org.eclipse.jdt.ls.core.internal.LanguageServer.setParentProcessId(long)" because the return value of "org.eclipse.jdt.ls.core.internal.JavaLanguageServerPlugin.getLanguageServer()" is null
	at org.eclipse.jdt.ls.core.internal.handlers.BaseInitHandler.handleInitializationOptions(BaseInitHandler.java:155)
	at org.eclipse.jdt.ls.core.internal.handlers.InitHandler.handleInitializationOptions(InitHandler.java:88)
	at org.eclipse.jdt.ls.core.internal.handlers.BaseInitHandler.initialize(BaseInitHandler.java:63)
	at org.eclipse.jdt.ls.core.internal.handlers.JDTLanguageServer.initialize(JDTLanguageServer.java:256)
	... 16 more

Nov 07, 2022 11:02:45 PM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint handleNotification
WARNING: Notification threw an exception: {
  "jsonrpc": "2.0",
  "method": "exit",
  "params": null
}
java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
	at org.eclipse.lsp4j.jsonrpc.services.GenericEndpoint.lambda$null$0(GenericEndpoint.java:67)
	at org.eclipse.lsp4j.jsonrpc.services.GenericEndpoint.notify(GenericEndpoint.java:152)
	at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.handleNotification(RemoteEndpoint.java:220)
	at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.consume(RemoteEndpoint.java:187)
	at org.eclipse.lsp4j.jsonrpc.json.StreamMessageProducer.handleMessage(StreamMessageProducer.java:194)
	at org.eclipse.lsp4j.jsonrpc.json.StreamMessageProducer.listen(StreamMessageProducer.java:94)
	at org.eclipse.lsp4j.jsonrpc.json.ConcurrentMessageProcessor.run(ConcurrentMessageProcessor.java:113)
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:539)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
	at java.base/java.lang.Thread.run(Thread.java:833)
Caused by: java.lang.reflect.InvocationTargetException
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:568)
	at org.eclipse.lsp4j.jsonrpc.services.GenericEndpoint.lambda$null$0(GenericEndpoint.java:65)
	... 11 more
Caused by: java.lang.NullPointerException: Cannot invoke "org.eclipse.jdt.ls.core.internal.LanguageServer.exit()" because the return value of "org.eclipse.jdt.ls.core.internal.JavaLanguageServerPlugin.getLanguageServer()" is null
	at org.eclipse.jdt.ls.core.internal.handlers.JDTLanguageServer.exit(JDTLanguageServer.java:453)
	... 16 more

[mickaelistria]

This tweak has unblocked me: mickaelistria@0f7b0aa ; but I think a better place where to store such processId would actually be the JDTLanguageServer instance (as we can now see other startup are possible, and maybe even imagine the plugin serving multiplt JDTLanguageServer at the same time)..

[rgrunber]

I think this makes sense. If a client wants to have their own "Application" to handle the JDT-LS startup, then that's valid, and we should support them.