java.util.concurrent.CompletionException: com.redhat.devtools.lsp4ij.server.CannotStartProcessException:

[angelozerr]

java.util.concurrent.CompletionException: com.redhat.devtools.lsp4ij.server.CannotStartProcessException: com.intellij.execution.process.ProcessNotCreatedException: Cannot run program "gopls": CreateProcess error=2, The system cannot find the file specified
	at java.base/java.util.concurrent.CompletableFuture.wrapInCompletionException(CompletableFuture.java:323)
	at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:376)
	at java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:391)
	at java.base/java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:657)
	at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:531)
	at java.base/java.util.concurrent.CompletableFuture.completeExceptionally(CompletableFuture.java:2221)
	at com.redhat.devtools.lsp4ij.LanguageServerWrapper.lambda$start$16(LanguageServerWrapper.java:539)
	at java.base/java.util.concurrent.CompletableFuture.uniExceptionally(CompletableFuture.java:1011)
	at java.base/java.util.concurrent.CompletableFuture$UniExceptionally.tryFire(CompletableFuture.java:995)
	at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:531)
	at java.base/java.util.concurrent.CompletableFuture.completeExceptionally(CompletableFuture.java:2221)
	at com.redhat.devtools.lsp4ij.LanguageServerWrapper.lambda$start$5(LanguageServerWrapper.java:433)
	at com.intellij.openapi.application.impl.ApplicationImpl$4.run(ApplicationImpl.java:381)
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:545)
	at com.intellij.util.concurrency.ContextCallable.lambda$call$1(ContextCallable.java:86)
	at com.intellij.concurrency.ThreadContext.installThreadContext(threadContext.kt:305)
	at com.intellij.util.concurrency.ContextCallable.lambda$call$2(ContextCallable.java:83)
	at com.intellij.util.concurrency.ContextCallable.call(ContextCallable.java:96)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:328)
	at com.intellij.util.concurrency.ChildContext$runInChildContext$1.invoke(propagation.kt:192)
	at com.intellij.util.concurrency.ChildContext$runInChildContext$1.invoke(propagation.kt:192)
	at com.intellij.util.concurrency.ChildContext.runInChildContext(propagation.kt:198)
	at com.intellij.util.concurrency.ChildContext.runInChildContext(propagation.kt:192)
	at com.intellij.util.concurrency.ContextRunnable.lambda$run$0(ContextRunnable.java:26)
	at com.intellij.concurrency.ThreadContext.resetThreadContext(threadContext.kt:294)
	at com.intellij.util.concurrency.ContextRunnable.run(ContextRunnable.java:25)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1090)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:614)
	at java.base/java.util.concurrent.Executors$PrivilegedThreadFactory$1.run(Executors.java:649)
	at java.base/java.lang.Thread.run(Thread.java:1474)
Caused by: com.redhat.devtools.lsp4ij.server.CannotStartProcessException: com.intellij.execution.process.ProcessNotCreatedException: Cannot run program "gopls": CreateProcess error=2, The system cannot find the file specified
	at com.redhat.devtools.lsp4ij.server.OSProcessStreamConnectionProvider.start(OSProcessStreamConnectionProvider.java:130)
	at com.redhat.devtools.lsp4ij.LanguageServerWrapper.lambda$start$5(LanguageServerWrapper.java:418)
	... 18 more
Caused by: com.intellij.execution.process.ProcessNotCreatedException: Cannot run program "gopls": CreateProcess error=2, The system cannot find the file specified
	at com.intellij.execution.configurations.GeneralCommandLine.createProcess(GeneralCommandLine.java:436)
	at com.intellij.execution.process.OSProcessHandler.startProcess(OSProcessHandler.java:85)
	at com.intellij.execution.process.OSProcessHandler.<init>(OSProcessHandler.java:45)
	at com.redhat.devtools.lsp4ij.server.OSProcessStreamConnectionProvider$1.<init>(OSProcessStreamConnectionProvider.java:114)
	at com.redhat.devtools.lsp4ij.server.OSProcessStreamConnectionProvider.start(OSProcessStreamConnectionProvider.java:114)
	... 19 more
Caused by: java.io.IOException: Cannot run program "gopls": CreateProcess error=2, The system cannot find the file specified
	at java.base/java.lang.ProcessBuilder.start(ProcessBuilder.java:1112)
	at java.base/java.lang.ProcessBuilder.start(ProcessBuilder.java:1046)
	at com.intellij.execution.configurations.GeneralCommandLine.createProcess(GeneralCommandLine.java:583)
	at com.intellij.execution.configurations.GeneralCommandLine.startProcess(GeneralCommandLine.java:599)
	at com.intellij.execution.configurations.GeneralCommandLine.startProcess(GeneralCommandLine.java:446)
	at com.intellij.execution.configurations.GeneralCommandLine.createProcess(GeneralCommandLine.java:416)
	... 23 more
Caused by: java.io.IOException: CreateProcess error=2, The system cannot find the file specified
	at java.base/java.lang.ProcessImpl.create(Native Method)
	at java.base/java.lang.ProcessImpl.<init>(ProcessImpl.java:485)
	at java.base/java.lang.ProcessImpl.start(ProcessImpl.java:146)
	at java.base/java.lang.ProcessBuilder.start(ProcessBuilder.java:1078)
	... 28 more

[angelozerr]

Unhandled exception in EDT

com.intellij.openapi.diagnostic.UnhandledException: com.redhat.devtools.lsp4ij.server.CannotStartProcessException: com.intellij.execution.process.ProcessNotCreatedException: Cannot run program "gopls": CreateProcess error=2, The system cannot find the file specified
	at com.intellij.openapi.application.impl.ExceptionsKt.processUnhandledException(exceptions.kt:55)
	at com.intellij.platform.ide.bootstrap.StartupErrorReporter.processException(StartupErrorReporter.java:338)
	at com.intellij.ide.IdeEventQueue.processException(IdeEventQueue.kt:466)
	at com.intellij.ide.IdeEventQueue.defaultDispatchEvent(IdeEventQueue.kt:728)
	at com.intellij.ide.IdeEventQueue._dispatchEvent(IdeEventQueue.kt:574)
	at com.intellij.ide.IdeEventQueue.dispatchEvent$lambda$0$0$0$0(IdeEventQueue.kt:382)
	at com.intellij.openapi.progress.impl.CoreProgressManager.computePrioritized(CoreProgressManager.java:928)
	at com.intellij.ide.IdeEventQueue.dispatchEvent$lambda$0$0$0(IdeEventQueue.kt:381)
	at com.intellij.ide.IdeEventQueueKt.performActivity$lambda$0(IdeEventQueue.kt:1111)
	at com.intellij.openapi.application.TransactionGuardImpl.performActivity(TransactionGuardImpl.java:106)
	at com.intellij.ide.IdeEventQueueKt.performActivity(IdeEventQueue.kt:1111)
	at com.intellij.ide.IdeEventQueue.dispatchEvent$lambda$0(IdeEventQueue.kt:376)
	at com.intellij.ide.IdeEventQueue.dispatchEvent(IdeEventQueue.kt:408)
	at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:207)
	at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
	at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
	at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
	at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
	at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:92)
Caused by: java.util.concurrent.CompletionException: com.redhat.devtools.lsp4ij.server.CannotStartProcessException: com.intellij.execution.process.ProcessNotCreatedException: Cannot run program "gopls": CreateProcess error=2, The system cannot find the file specified
	at java.base/java.util.concurrent.CompletableFuture.wrapInCompletionException(CompletableFuture.java:323)
	at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:376)
	at java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:391)
	at java.base/java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:657)
	at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:531)
	at java.base/java.util.concurrent.CompletableFuture.completeExceptionally(CompletableFuture.java:2221)
	at com.redhat.devtools.lsp4ij.LanguageServerWrapper.lambda$start$16(LanguageServerWrapper.java:539)
	at java.base/java.util.concurrent.CompletableFuture.uniExceptionally(CompletableFuture.java:1011)
	at java.base/java.util.concurrent.CompletableFuture$UniExceptionally.tryFire(CompletableFuture.java:995)
	at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:531)
	at java.base/java.util.concurrent.CompletableFuture.completeExceptionally(CompletableFuture.java:2221)
	at com.redhat.devtools.lsp4ij.LanguageServerWrapper.lambda$start$5(LanguageServerWrapper.java:433)
	at com.intellij.openapi.application.impl.ApplicationImpl$4.run(ApplicationImpl.java:381)
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:545)
	at com.intellij.util.concurrency.ContextCallable.lambda$call$1(ContextCallable.java:86)
	at com.intellij.concurrency.ThreadContext.installThreadContext(threadContext.kt:305)
	at com.intellij.util.concurrency.ContextCallable.lambda$call$2(ContextCallable.java:83)
	at com.intellij.util.concurrency.ContextCallable.call(ContextCallable.java:96)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:328)
	at com.intellij.util.concurrency.ChildContext$runInChildContext$1.invoke(propagation.kt:192)
	at com.intellij.util.concurrency.ChildContext$runInChildContext$1.invoke(propagation.kt:192)
	at com.intellij.util.concurrency.ChildContext.runInChildContext(propagation.kt:198)
	at com.intellij.util.concurrency.ChildContext.runInChildContext(propagation.kt:192)
	at com.intellij.util.concurrency.ContextRunnable.lambda$run$0(ContextRunnable.java:26)
	at com.intellij.concurrency.ThreadContext.resetThreadContext(threadContext.kt:294)
	at com.intellij.util.concurrency.ContextRunnable.run(ContextRunnable.java:25)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1090)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:614)
	at java.base/java.util.concurrent.Executors$PrivilegedThreadFactory$1.run(Executors.java:649)
	at java.base/java.lang.Thread.run(Thread.java:1474)
Caused by: com.redhat.devtools.lsp4ij.server.CannotStartProcessException: com.intellij.execution.process.ProcessNotCreatedException: Cannot run program "gopls": CreateProcess error=2, The system cannot find the file specified
	at com.redhat.devtools.lsp4ij.server.OSProcessStreamConnectionProvider.start(OSProcessStreamConnectionProvider.java:130)
	at com.redhat.devtools.lsp4ij.LanguageServerWrapper.lambda$start$5(LanguageServerWrapper.java:418)
	... 18 more
Caused by: com.intellij.execution.process.ProcessNotCreatedException: Cannot run program "gopls": CreateProcess error=2, The system cannot find the file specified
	at com.intellij.execution.configurations.GeneralCommandLine.createProcess(GeneralCommandLine.java:436)
	at com.intellij.execution.process.OSProcessHandler.startProcess(OSProcessHandler.java:85)
	at com.intellij.execution.process.OSProcessHandler.<init>(OSProcessHandler.java:45)
	at com.redhat.devtools.lsp4ij.server.OSProcessStreamConnectionProvider$1.<init>(OSProcessStreamConnectionProvider.java:114)
	at com.redhat.devtools.lsp4ij.server.OSProcessStreamConnectionProvider.start(OSProcessStreamConnectionProvider.java:114)
	... 19 more
Caused by: java.io.IOException: Cannot run program "gopls": CreateProcess error=2, The system cannot find the file specified
	at java.base/java.lang.ProcessBuilder.start(ProcessBuilder.java:1112)
	at java.base/java.lang.ProcessBuilder.start(ProcessBuilder.java:1046)
	at com.intellij.execution.configurations.GeneralCommandLine.createProcess(GeneralCommandLine.java:583)
	at com.intellij.execution.configurations.GeneralCommandLine.startProcess(GeneralCommandLine.java:599)
	at com.intellij.execution.configurations.GeneralCommandLine.startProcess(GeneralCommandLine.java:446)
	at com.intellij.execution.configurations.GeneralCommandLine.createProcess(GeneralCommandLine.java:416)
	... 23 more
Caused by: java.io.IOException: CreateProcess error=2, The system cannot find the file specified
	at java.base/java.lang.ProcessImpl.create(Native Method)
	at java.base/java.lang.ProcessImpl.<init>(ProcessImpl.java:485)
	at java.base/java.lang.ProcessImpl.start(ProcessImpl.java:146)
	at java.base/java.lang.ProcessBuilder.start(ProcessBuilder.java:1078)
	... 28 more

[SergejSalnikov]

The core problem

Look at LanguageServerWrapper.java lines 436-543

this.initializeFuture = startFuture       // line 436
    .thenApply(...)
    .thenCompose(...)
    .thenApply(...)
    .thenApply(...)
    .thenRun(...)
    .exceptionally(e -> {                  // line 529
        // ...
        initializeFuture.completeExceptionally(serverError);  // line 539 ← BUG
        // ...
        return null;                       // line 542
    });

this.initializeFuture is assigned to the result of the entire chain, including the .exceptionally() handler. The .exceptionally() handler is supposed to be a recovery — it receives the error, handles it (logs, shows notification), and returns null, which would make initializeFuture complete normally with null.

But before returning null, line 539 calls initializeFuture.completeExceptionally(serverError). This force-completes the very same future with an exception, overriding the normal recovery. The return null on line 542 is now a no-op because the future is already completed.

How this causes both exceptions

Exception 1 is the stack trace of line 539 itself firing. The CompletionException in Exception 1's stack trace is created at UniApply.tryFire — meaning some other code elsewhere has chained a .thenApply() on initializeFuture. When initializeFuture is force-completed exceptionally, that dependent fires and wraps the error in a CompletionException. That dependent doesn't handle the exception either, so it propagates.

Exception 2 is the consequence: that unhandled CompletionException reaches the EDT (likely via a .thenAccept()/.whenComplete() scheduled on the EDT to update UI), and since nothing catches it, it crashes as an UnhandledException.

Why the wrapping is wrong

The .exceptionally() handler's contract is:

• Catch the error → ✅ it does this
• Handle it (log, notify) → ✅ it does this
• Recover by returning a value → ❌ defeated by line 539

By calling initializeFuture.completeExceptionally(), the handler re-injects the error into the very future it was supposed to protect. The exception escapes the error boundary and reaches consumers of initializeFuture that rightfully expect the .exceptionally() handler to have dealt with it.

Proposed fix

Remove line 539 (initializeFuture.completeExceptionally(serverError)). The .exceptionally() handler already does the right things (stores serverError, shows notification, stops the server). The return null will let initializeFuture complete normally, and any consumer of initializeFuture will get null (meaning "server didn't start") rather than an unhandled exception blowing up on the EDT.

If some downstream consumers of initializeFuture need to know the server failed, they should check serverError or ServerStatus rather than relying on the future completing exceptionally.