NPE in CompletionResolveHandler

[AlexTugarev]

In Theia, when suggestions are shown and you are typing, there are LS error during resolution of completion items. This following error stack is in the error messages sent back to client.

java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
	at org.eclipse.lsp4j.jsonrpc.services.GenericEndpoint.lambda$null$0(GenericEndpoint.java:63)
	at org.eclipse.lsp4j.jsonrpc.services.GenericEndpoint.request(GenericEndpoint.java:116)
	at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.handleRequest(RemoteEndpoint.java:252)
	at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.consume(RemoteEndpoint.java:181)
	at org.eclipse.jdt.ls.core.internal.ParentProcessWatcher.lambda$0(ParentProcessWatcher.java:83)
	at org.eclipse.lsp4j.jsonrpc.json.StreamMessageProducer.handleMessage(StreamMessageProducer.java:183)
	at org.eclipse.lsp4j.jsonrpc.json.StreamMessageProducer.listen(StreamMessageProducer.java:92)
	at org.eclipse.lsp4j.jsonrpc.json.ConcurrentMessageProcessor.run(ConcurrentMessageProcessor.java:95)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.reflect.InvocationTargetException
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.eclipse.lsp4j.jsonrpc.services.GenericEndpoint.lambda$null$0(GenericEndpoint.java:61)
	... 12 more
Caused by: java.util.concurrent.CompletionException: java.lang.NullPointerException
	at java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:273)
	at java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:280)
	at java.util.concurrent.CompletableFuture.uniApply(CompletableFuture.java:604)
	at java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:577)
	at java.util.concurrent.CompletableFuture$Completion.exec(CompletableFuture.java:443)
	at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
	at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
	at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
	at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)
Caused by: java.lang.NullPointerException
	at org.eclipse.jdt.ls.core.internal.handlers.CompletionResolveHandler.resolve(CompletionResolveHandler.java:72)
	at org.eclipse.jdt.ls.core.internal.handlers.JDTLanguageServer.lambda$5(JDTLanguageServer.java:434)
	at org.eclipse.jdt.ls.core.internal.handlers.JDTLanguageServer.lambda$21(JDTLanguageServer.java:703)
	at java.util.concurrent.CompletableFuture.uniApply(CompletableFuture.java:602)
	... 6 more

[fbricon]

The NPE is easy to fix, but the real problem here is why isn't the data returned as a Map:

https://github.com/eclipse/eclipse.jdt.ls/blob/6c64df5646a024c0fef032298aedadeee9250d1e/org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/handlers/CompletionResolveHandler.java#L69-L72

Can you paste the json payload sent to the server during completion resolution?

[AlexTugarev]

In error case, there is no data attached. Which means, first call of completionItem/resolve after textDocument/completion contains the data entry, but not the subsequent ones fired when I continue typing.

textDocument/completion

item looked up from completion result

completionItem/resolve

error response

[fbricon]

@AlexTugarev that sounds like a bug in Theia then. Again, we can fix the NPE on jdt.ls side but Theia needs to send the data that was returned during the completion.
cc @tsmaeder

[AlexTugarev]

Thanks for the info, @fbricon! I'll try with latest monaco version. This problem seems to be related with automatic refines of completion items. So, some items were already resolved, and when you continue typing it will re-resolve them again.