Add virtual environment validation notification for Python resources

src/Aspire.Hosting.Python/PythonAppResourceBuilderExtensions.cs

@@ -4,8 +4,10 @@
 using System.ComponentModel;
 using System.Runtime.CompilerServices;
 #pragma warning disable ASPIREEXTENSION001
+#pragma warning disable ASPIREINTERACTION001
 using Aspire.Hosting.ApplicationModel;
 using Aspire.Hosting.Python;
+using Microsoft.Extensions.DependencyInjection;
 
 namespace Aspire.Hosting;
 
@@ -256,6 +258,48 @@ private static IResourceBuilder<PythonAppResource> AddPythonAppCore(
             // This will set up the the entrypoint based on the PythonEntrypointAnnotation
             .WithEntrypoint(entrypointType, entrypoint);
 
+        // Add virtual environment validation before resource starts
+        resourceBuilder.OnBeforeResourceStarted(async (resource, evt, ct) =>
+        {
+            // Only check if interaction service is available (dashboard is enabled)
+            var interactionService = evt.Services.GetService<IInteractionService>();
+            if (interactionService is null || !interactionService.IsAvailable)
+            {
+                return;
+            }
+
+            // Get the virtual environment path from the annotation
+            if (!resource.TryGetLastAnnotation<PythonEnvironmentAnnotation>(out var pythonEnv) ||
+                pythonEnv.VirtualEnvironment is null)
+            {
+                return;
+            }
+
+            // Skip check if UV is being used (it creates the virtual environment automatically)
+            if (pythonEnv.Uv)
+            {
+                return;
+            }
+
+            var venvPath = pythonEnv.VirtualEnvironment.Location;
+
+            // Check if the virtual environment directory exists
+            if (!Directory.Exists(venvPath))
+            {
+                var title = "Python virtual environment not found";
+                var message = $"The Python virtual environment for resource '{resource.Name}' was not found at '{venvPath}'. Please create the virtual environment before running the application.";
+                var options = new NotificationInteractionOptions
+                {
+                    Intent = MessageIntent.Error,
+                    LinkText = "Learn more",
+                    LinkUrl = "https://aka.ms/aspire/python"
+                };
+
+                // Show notification without blocking (fire and forget)
+                _ = interactionService.PromptNotificationAsync(title, message, options, ct);
+            }
+        });
+
         resourceBuilder.WithIconName("CodePyRectangle");
 
         resourceBuilder.WithOtlpExporter();

src/Aspire.Hosting.Python/VirtualEnvironment.cs

@@ -9,6 +9,11 @@ namespace Aspire.Hosting.Python;
 /// <param name="virtualEnvironmentPath">The path to the directory containing the python app files.</param>
 internal sealed class VirtualEnvironment(string virtualEnvironmentPath)
 {
+    /// <summary>
+    /// Gets the path to the virtual environment directory.
+    /// </summary>
+    public string Location { get; } = virtualEnvironmentPath;
+
     /// <summary>
     /// Locates an executable in the virtual environment.
     /// </summary>
@@ -18,9 +23,9 @@ public string GetExecutable(string name)
     {
         if (OperatingSystem.IsWindows())
         {
-            return Path.Join(virtualEnvironmentPath, "Scripts", name + ".exe");
+            return Path.Join(Location, "Scripts", name + ".exe");
         }
 
-        return Path.Join(virtualEnvironmentPath, "bin", name);
+        return Path.Join(Location, "bin", name);
     }
 }

tests/Aspire.Hosting.Python.Tests/AddPythonAppTests.cs

@@ -3,13 +3,15 @@
 
 #pragma warning disable CS0612
 #pragma warning disable CS0618 // Type or member is obsolete
+#pragma warning disable ASPIREINTERACTION001 // Type is for evaluation purposes only and is subject to change or removal in future updates. Suppress this diagnostic to proceed.
 
 using Microsoft.Extensions.DependencyInjection;
 using Aspire.Hosting.Utils;
 using Aspire.Hosting.Tests.Utils;
 using System.Diagnostics;
 using Aspire.TestUtilities;
 using Aspire.Hosting.ApplicationModel;
+using Aspire.Hosting.Tests;
 
 namespace Aspire.Hosting.Python.Tests;
 
@@ -1149,5 +1151,128 @@ public async Task PythonApp_DoesNotSetPythonUtf8EnvironmentVariable_InPublishMod
         // PYTHONUTF8 should not be set in Publish mode, even on Windows
         Assert.False(environmentVariables.ContainsKey("PYTHONUTF8"));
     }
+
+    [Fact]
+    public async Task PythonApp_ShowsNotification_WhenVirtualEnvironmentDoesNotExist()
+    {
+        using var builder = TestDistributedApplicationBuilder.Create().WithTestAndResourceLogging(outputHelper);
+        using var tempDir = new TempDirectory();
+
+        // Create a script file but don't create the virtual environment
+        var scriptPath = Path.Combine(tempDir.Path, "main.py");
+        File.WriteAllText(scriptPath, "print('Hello, World!')");
+
+        var pythonApp = builder.AddPythonScript("pythonProject", tempDir.Path, "main.py");
+
+        using var app = builder.Build();
+
+        // Verify the resource has the expected annotation
+        Assert.True(pythonApp.Resource.TryGetLastAnnotation<PythonEnvironmentAnnotation>(out var annotation));
+        Assert.NotNull(annotation.VirtualEnvironment);
+
+        // Verify the virtual environment path doesn't exist
+        var expectedVenvPath = Path.Combine(tempDir.Path, ".venv");
+        Assert.False(Directory.Exists(expectedVenvPath), "Virtual environment should not exist for this test");
+    }
+
+    [Fact]
+    public async Task PythonApp_SendsNotification_WhenVirtualEnvironmentDoesNotExist()
+    {
+        var testInteractionService = new TestInteractionService();
+
+        using var builder = TestDistributedApplicationBuilder.Create().WithTestAndResourceLogging(outputHelper);
+        builder.Services.AddSingleton<IInteractionService>(testInteractionService);
+
+        using var tempDir = new TempDirectory();
+
+        // Create a script file but don't create the virtual environment
+        var scriptPath = Path.Combine(tempDir.Path, "main.py");
+        File.WriteAllText(scriptPath, "print('Hello, World!')");
+
+        var pythonApp = builder.AddPythonScript("pythonProject", tempDir.Path, "main.py");
+
+        using var app = builder.Build();
+
+        // Start the app to trigger the BeforeResourceStartedEvent
+        await app.StartAsync();
+
+        // Read the notification from the interaction service
+        var hasNotification = await testInteractionService.Interactions.Reader.WaitToReadAsync().AsTask().WaitAsync(TimeSpan.FromSeconds(5));
+        Assert.True(hasNotification, "Should have received a notification");
+
+        var notification = await testInteractionService.Interactions.Reader.ReadAsync();
+
+        // Verify the notification properties
+        Assert.Equal("Python virtual environment not found", notification.Title);
+        Assert.Contains("pythonProject", notification.Message);
+        Assert.Contains(tempDir.Path, notification.Message);
+
+        // Verify notification options
+        Assert.NotNull(notification.Options);
+        var notificationOptions = Assert.IsType<NotificationInteractionOptions>(notification.Options);
+        Assert.Equal(MessageIntent.Error, notificationOptions.Intent);
+        Assert.Equal("Learn more", notificationOptions.LinkText);
+        Assert.Equal("https://aka.ms/aspire/python", notificationOptions.LinkUrl);
+
+        await app.StopAsync();
+    }
+
+    [Fact]
+    public async Task PythonApp_DoesNotSendNotification_WhenInteractionServiceNotAvailable()
+    {
+        var testInteractionService = new TestInteractionService { IsAvailable = false };
+
+        using var builder = TestDistributedApplicationBuilder.Create().WithTestAndResourceLogging(outputHelper);
+        builder.Services.AddSingleton<IInteractionService>(testInteractionService);
+
+        using var tempDir = new TempDirectory();
+
+        // Create a script file but don't create the virtual environment
+        var scriptPath = Path.Combine(tempDir.Path, "main.py");
+        File.WriteAllText(scriptPath, "print('Hello, World!')");
+
+        var pythonApp = builder.AddPythonScript("pythonProject", tempDir.Path, "main.py");
+
+        using var app = builder.Build();
+
+        // Start the app to trigger the BeforeResourceStartedEvent
+        await app.StartAsync();
+
+        // Give a moment for any potential notification
+        await Task.Delay(500);
+
+        // Verify no notification was sent
+        var hasNotification = testInteractionService.Interactions.Reader.TryRead(out _);
+        Assert.False(hasNotification, "Should not have received a notification when IsAvailable is false");
+
+        await app.StopAsync();
+    }
+
+    [Fact]
+    public void PythonApp_DoesNotSendNotification_WhenUsingUvEnvironment()
+    {
+        var testInteractionService = new TestInteractionService();
+
+        using var builder = TestDistributedApplicationBuilder.Create().WithTestAndResourceLogging(outputHelper);
+        builder.Services.AddSingleton<IInteractionService>(testInteractionService);
+
+        using var tempDir = new TempDirectory();
+
+        // Create a script file
+        var scriptPath = Path.Combine(tempDir.Path, "main.py");
+        File.WriteAllText(scriptPath, "print('Hello, World!')");
+
+        var pythonApp = builder.AddPythonScript("pythonProject", tempDir.Path, "main.py")
+            .WithUvEnvironment(); // UV creates the venv automatically
+
+        using var app = builder.Build();
+
+        // Verify the PythonEnvironmentAnnotation has Uv set to true
+        Assert.True(pythonApp.Resource.TryGetLastAnnotation<PythonEnvironmentAnnotation>(out var annotation));
+        Assert.True(annotation.Uv, "UV should be enabled");
+
+        // The actual notification check would happen at runtime, but since UV is enabled,
+        // the check would be skipped even if the venv doesn't exist
+    }
 }
 

tests/Aspire.Hosting.Python.Tests/Aspire.Hosting.Python.Tests.csproj

@@ -20,6 +20,7 @@
 
   <ItemGroup>
       <Compile Include="$(TestsSharedDir)\TestModuleInitializer.cs" />
+      <Compile Include="$(TestsSharedDir)\TestInteractionService.cs" />
   </ItemGroup>
 
 </Project>