Catch exceptions within completion handler

We'll still see the same error in the log, but as a warning and not as
an exception bubbled up over LSP that causes some clients, like Kate, to
crash. We can't do anything about PowerShell's completion failing.

src/PowerShellEditorServices/Services/TextDocument/Handlers/CompletionHandler.cs

@@ -69,16 +69,25 @@ public override async Task<CompletionList> Handle(CompletionParams request, Canc
             int cursorColumn = request.Position.Character + 1;
 
             ScriptFile scriptFile = _workspaceService.GetFile(request.TextDocument.Uri);
-            (bool isIncomplete, IReadOnlyList<CompletionItem> completionResults) = await GetCompletionsInFileAsync(
-                scriptFile,
-                cursorLine,
-                cursorColumn,
-                cancellationToken).ConfigureAwait(false);
-
-            // Treat completions trigged by space as incomplete so that `gci `
-            // and then typing `-` doesn't just filter the list of parameter values
-            // (typically files) returned by the space completion
-            return new CompletionList(completionResults, isIncomplete || request?.Context?.TriggerCharacter is " ");
+            try
+            {
+                (bool isIncomplete, IReadOnlyList<CompletionItem> completionResults) = await GetCompletionsInFileAsync(
+                    scriptFile,
+                    cursorLine,
+                    cursorColumn,
+                    cancellationToken).ConfigureAwait(false);
+
+                // Treat completions triggered by space as incomplete so that `gci `
+                // and then typing `-` doesn't just filter the list of parameter values
+                // (typically files) returned by the space completion
+                return new CompletionList(completionResults, isIncomplete || request?.Context?.TriggerCharacter is " ");
+            }
+            // We can't do anything about completions failing.
+            catch (Exception e)
+            {
+                _logger.LogWarning(e, "Exception occurred while running handling completion request");
+                return new CompletionList();
+            }
         }
 
         // Handler for "completionItem/resolve". In VSCode this is fired when a completion item is highlighted in the completion list.

test/PowerShellEditorServices.Test.E2E/LSPTestsFixures.cs

@@ -33,8 +33,9 @@ public class LSPTestsFixture : IAsyncLifetime
         private const bool IsDebugAdapterTests = false;
 
         public ILanguageClient PsesLanguageClient { get; private set; }
-        public List<Diagnostic> Diagnostics { get; set; }
-        internal List<PsesTelemetryEvent> TelemetryEvents { get; set; }
+        public List<LogMessageParams> Messages = new();
+        public List<Diagnostic> Diagnostics = new();
+        internal List<PsesTelemetryEvent> TelemetryEvents = new();
         public ITestOutputHelper Output { get; set; }
 
         protected PsesStdioProcess _psesProcess;
@@ -46,20 +47,21 @@ public async Task InitializeAsync()
             _psesProcess = new PsesStdioProcess(factory, IsDebugAdapterTests);
             await _psesProcess.Start().ConfigureAwait(false);
 
-            Diagnostics = new List<Diagnostic>();
-            TelemetryEvents = new List<PsesTelemetryEvent>();
-            DirectoryInfo testdir =
+            DirectoryInfo testDir =
                 Directory.CreateDirectory(Path.Combine(s_binDir, Path.GetRandomFileName()));
 
             PsesLanguageClient = LanguageClient.PreInit(options =>
             {
                 options
                     .WithInput(_psesProcess.OutputStream)
                     .WithOutput(_psesProcess.InputStream)
-                    .WithWorkspaceFolder(DocumentUri.FromFileSystemPath(testdir.FullName), "testdir")
+                    .WithWorkspaceFolder(DocumentUri.FromFileSystemPath(testDir.FullName), "testdir")
                     .WithInitializationOptions(new { EnableProfileLoading = false })
                     .OnPublishDiagnostics(diagnosticParams => Diagnostics.AddRange(diagnosticParams.Diagnostics.Where(d => d != null)))
-                    .OnLogMessage(logMessageParams => Output?.WriteLine($"{logMessageParams.Type}: {logMessageParams.Message}"))
+                    .OnLogMessage(logMessageParams => {
+                        Output?.WriteLine($"{logMessageParams.Type}: {logMessageParams.Message}");
+                        Messages.Add(logMessageParams);
+                    })
                     .OnTelemetryEvent(telemetryEventParams => TelemetryEvents.Add(
                         new PsesTelemetryEvent
                         {

test/PowerShellEditorServices.Test.E2E/LanguageServerProtocolMessageTests.cs

@@ -38,6 +38,7 @@ public class LanguageServerProtocolMessageTests : IClassFixture<LSPTestsFixture>
             Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location);
 
         private readonly ILanguageClient PsesLanguageClient;
+        private readonly List<LogMessageParams> Messages;
         private readonly List<Diagnostic> Diagnostics;
         private readonly List<PsesTelemetryEvent> TelemetryEvents;
         private readonly string PwshExe;
@@ -46,6 +47,8 @@ public LanguageServerProtocolMessageTests(ITestOutputHelper output, LSPTestsFixt
         {
             data.Output = output;
             PsesLanguageClient = data.PsesLanguageClient;
+            Messages = data.Messages;
+            Messages.Clear();
             Diagnostics = data.Diagnostics;
             Diagnostics.Clear();
             TelemetryEvents = data.TelemetryEvents;
@@ -957,6 +960,35 @@ public async Task CanSendCompletionAndCompletionResolveRequestAsync()
             Assert.Contains("Writes customized output to a host", updatedCompletionItem.Documentation.String);
         }
 
+        // Regression test for https://github.com/PowerShell/PowerShellEditorServices/issues/1926
+        [Fact]
+        public async Task CanRequestCompletionsAndHandleExceptions()
+        {
+            string filePath = NewTestFile(@"
+@() | ForEach-Object {
+    if ($false) {
+      return
+    }
+
+    @{key=$}
+  }");
+
+            Messages.Clear(); //  On some systems there's a warning message about configuration items too.
+            CompletionList completionItems = await PsesLanguageClient.TextDocument.RequestCompletion(
+                new CompletionParams
+                {
+                    TextDocument = new TextDocumentIdentifier
+                    {
+                        Uri = DocumentUri.FromFileSystemPath(filePath)
+                    },
+                    Position = new Position(line: 6, character: 11)
+                });
+
+            Assert.Empty(completionItems);
+            LogMessageParams message = Assert.Single(Messages);
+            Assert.Contains("Exception occurred while running handling completion request", message.Message);
+        }
+
         [SkippableFact(Skip = "Completion for Expand-SlowArchive is flaky.")]
         public async Task CanSendCompletionResolveWithModulePrefixRequestAsync()
         {