Graceful error handling for offline scenarios in 'aspire new' and 'aspire add' commands

src/Aspire.Cli/Commands/AddCommand.cs

@@ -88,6 +88,11 @@ protected override async Task<int> ExecuteAsync(ParseResult parseResult, Cancell
                 () => _nuGetPackageCache.GetIntegrationPackagesAsync(effectiveAppHostProjectFile.Directory!, prerelease, source, cancellationToken)
                 );
 
+            if (!packages.Any())
+            {
+                throw new EmptyChoicesException("No integration packages were found. Please check your internet connection or NuGet source configuration.");
+            }
+
             var version = parseResult.GetValue<string?>("--version");
 
             var packagesWithShortName = packages.Select(GenerateFriendlyName);
@@ -174,6 +179,11 @@ protected override async Task<int> ExecuteAsync(ParseResult parseResult, Cancell
             _interactionService.DisplayCancellationMessage();
             return ExitCodeConstants.FailedToAddPackage;
         }
+        catch (EmptyChoicesException ex)
+        {
+            _interactionService.DisplayError(ex.Message);
+            return ExitCodeConstants.FailedToAddPackage;
+        }
         catch (Exception ex)
         {
             _interactionService.DisplayLines(outputCollector.GetLines());

src/Aspire.Cli/Commands/NewCommand.cs

@@ -126,6 +126,11 @@ private async Task<string> GetProjectTemplatesVersionAsync(ParseResult parseResu
                 () => _nuGetPackageCache.GetTemplatePackagesAsync(workingDirectory, prerelease, source, cancellationToken)
                 );
 
+            if (!candidatePackages.Any())
+            {
+                throw new EmptyChoicesException("No template versions were found. Please check your internet connection or NuGet source configuration.");
+            }
+
             var orderedCandidatePackages = candidatePackages.OrderByDescending(p => SemVersion.Parse(p.Version), SemVersion.PrecedenceComparer);
             var selectedPackage = await _prompter.PromptForTemplatesVersionAsync(orderedCandidatePackages, cancellationToken);
             return selectedPackage.Version;
@@ -209,6 +214,11 @@ protected override async Task<int> ExecuteAsync(ParseResult parseResult, Cancell
             _interactionService.DisplayError($"An error occurred while trusting the certificates: {ex.Message}");
             return ExitCodeConstants.FailedToTrustCertificates;
         }
+        catch (EmptyChoicesException ex)
+        {
+            _interactionService.DisplayError(ex.Message);
+            return ExitCodeConstants.FailedToCreateNewProject;
+        }
     }
 }
 

src/Aspire.Cli/Interaction/EmptyChoicesException.cs

@@ -0,0 +1,8 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace Aspire.Cli.Interaction;
+
+internal sealed class EmptyChoicesException(string message) : Exception(message)
+{
+}

src/Aspire.Cli/Interaction/InteractionService.cs

@@ -58,6 +58,12 @@ public async Task<T> PromptForSelectionAsync<T>(string promptText, IEnumerable<T
         ArgumentNullException.ThrowIfNull(choices, nameof(choices));
         ArgumentNullException.ThrowIfNull(choiceFormatter, nameof(choiceFormatter));
 
+        // Check if the choices collection is empty to avoid throwing an InvalidOperationException
+        if (!choices.Any())
+        {
+            throw new EmptyChoicesException($"No items available for selection: {promptText}");
+        }
+
         var prompt = new SelectionPrompt<T>()
             .Title(promptText)
             .UseConverter(choiceFormatter)

tests/Aspire.Cli.Tests/Commands/AddCommandTests.cs

@@ -477,6 +477,42 @@ public async Task AddCommandPromptsForDisambiguation()
         Assert.Equal("9.2.0", addedPackageVersion);
     }
 
+    [Fact]
+    public async Task AddCommand_EmptyPackageList_DisplaysErrorMessage()
+    {
+        string? displayedErrorMessage = null;
+
+        var services = CliTestHelper.CreateServiceCollection(outputHelper, options => {
+            options.InteractionServiceFactory = (sp) => {
+                var testInteractionService = new TestInteractionService();
+                testInteractionService.DisplayErrorCallback = (message) => {
+                    displayedErrorMessage = message;
+                };
+                return testInteractionService;
+            };
+
+            options.ProjectLocatorFactory = _ => new TestProjectLocator();
+
+            options.DotNetCliRunnerFactory = (sp) =>
+            {
+                var runner = new TestDotNetCliRunner();
+                runner.SearchPackagesAsyncCallback = (dir, query, prerelease, take, skip, nugetSource, options, cancellationToken) =>
+                {
+                    return (0, Array.Empty<NuGetPackage>());
+                };
+
+                return runner;
+            };
+        });
+        var provider = services.BuildServiceProvider();
+
+        var command = provider.GetRequiredService<AddCommand>();
+        var result = command.Parse("add");
+
+        var exitCode = await result.InvokeAsync().WaitAsync(CliTestConstants.DefaultTimeout);
+        Assert.Equal(ExitCodeConstants.FailedToAddPackage, exitCode);
+        Assert.Contains("No integration packages were found", displayedErrorMessage);
+    }
 }
 
 internal sealed class TestAddCommandPrompter(IInteractionService interactionService) : AddCommandPrompter(interactionService)

tests/Aspire.Cli.Tests/Commands/NewCommandTests.cs

@@ -589,6 +589,40 @@ public async Task NewCommandDoesNotPromptForTemplateVersionIfSpecifiedOnCommandL
         Assert.False(promptedForTemplateVersion);
     }
 
+    [Fact]
+    public async Task NewCommand_EmptyPackageList_DisplaysErrorMessage()
+    {
+        string? displayedErrorMessage = null;
+
+        var services = CliTestHelper.CreateServiceCollection(outputHelper, options => {
+            options.InteractionServiceFactory = (sp) => {
+                var testInteractionService = new TestInteractionService();
+                testInteractionService.DisplayErrorCallback = (message) => {
+                    displayedErrorMessage = message;
+                };
+                return testInteractionService;
+            };
+
+            options.DotNetCliRunnerFactory = (sp) => {
+                var runner = new TestDotNetCliRunner();
+                runner.SearchPackagesAsyncCallback = (dir, query, prerelease, take, skip, nugetSource, options, cancellationToken) => {
+                    return (0, Array.Empty<NuGetPackage>());
+                };
+                return runner;
+            };
+        });
+
+        var provider = services.BuildServiceProvider();
+
+        var command = provider.GetRequiredService<NewCommand>();
+        var result = command.Parse("new");
+
+        var exitCode = await result.InvokeAsync().WaitAsync(CliTestConstants.DefaultTimeout);
+
+        Assert.Equal(ExitCodeConstants.FailedToCreateNewProject, exitCode);
+        Assert.Contains("No template versions were found", displayedErrorMessage);
+    }
+
     [Fact]
     public async Task NewCommand_WhenCertificateServiceThrows_ReturnsNonZeroExitCode()
     {

tests/Aspire.Cli.Tests/Interaction/InteractionServiceTests.cs

@@ -0,0 +1,23 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Aspire.Cli.Interaction;
+using Spectre.Console;
+using Xunit;
+
+namespace Aspire.Cli.Tests.Interaction;
+
+public class InteractionServiceTests
+{
+    [Fact]
+    public async Task PromptForSelectionAsync_EmptyChoices_ThrowsEmptyChoicesException()
+    {
+        // Arrange
+        var interactionService = new InteractionService(AnsiConsole.Console);
+        var choices = Array.Empty<string>();
+
+        // Act & Assert
+        await Assert.ThrowsAsync<EmptyChoicesException>(() => 
+            interactionService.PromptForSelectionAsync("Select an item:", choices, x => x, CancellationToken.None));
+    }
+}

tests/Aspire.Cli.Tests/TestServices/TestInteractionService.cs

@@ -0,0 +1,68 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Aspire.Cli.Backchannel;
+using Aspire.Cli.Interaction;
+using Spectre.Console;
+
+namespace Aspire.Cli.Tests.TestServices;
+
+internal sealed class TestInteractionService : IInteractionService
+{
+    public Action<string>? DisplayErrorCallback { get; set; }
+
+    public Task<T> ShowStatusAsync<T>(string statusText, Func<Task<T>> action)
+    {
+        return action();
+    }
+
+    public void ShowStatus(string statusText, Action action)
+    {
+        action();
+    }
+
+    public Task<string> PromptForStringAsync(string promptText, string? defaultValue = null, Func<string, ValidationResult>? validator = null, CancellationToken cancellationToken = default)
+    {
+        return Task.FromResult(defaultValue ?? string.Empty);
+    }
+
+    public Task<T> PromptForSelectionAsync<T>(string promptText, IEnumerable<T> choices, Func<T, string> choiceFormatter, CancellationToken cancellationToken = default) where T : notnull
+    {
+        if (!choices.Any())
+        {
+            throw new EmptyChoicesException($"No items available for selection: {promptText}");
+        }
+
+        return Task.FromResult(choices.First());
+    }
+
+    public int DisplayIncompatibleVersionError(AppHostIncompatibleException ex, string appHostHostingSdkVersion)
+    {
+        return 0;
+    }
+
+    public void DisplayError(string errorMessage)
+    {
+        DisplayErrorCallback?.Invoke(errorMessage);
+    }
+
+    public void DisplayMessage(string emoji, string message)
+    {
+    }
+
+    public void DisplaySuccess(string message)
+    {
+    }
+
+    public void DisplayDashboardUrls((string BaseUrlWithLoginToken, string? CodespacesUrlWithLoginToken) dashboardUrls)
+    {
+    }
+
+    public void DisplayLines(IEnumerable<(string Stream, string Line)> lines)
+    {
+    }
+
+    public void DisplayCancellationMessage()
+    {
+    }
+}