Better malformed launchsettings error

src/Aspire.Hosting/LaunchProfileExtensions.cs

@@ -30,26 +30,37 @@ internal static class LaunchProfileExtensions
 
     internal static NamedLaunchProfile? GetEffectiveLaunchProfile(this ProjectResource projectResource, bool throwIfNotFound = false)
     {
-        string? launchProfileName = projectResource.SelectLaunchProfileName();
-        if (string.IsNullOrEmpty(launchProfileName))
+        try
         {
-            return null;
-        }
+            string? launchProfileName = projectResource.SelectLaunchProfileName();
+            if (string.IsNullOrEmpty(launchProfileName))
+            {
+                return null;
+            }
 
-        var profiles = projectResource.GetLaunchSettings()?.Profiles;
-        if (profiles is null)
-        {
-            return null;
-        }
+            var profiles = projectResource.GetLaunchSettings()?.Profiles;
+            if (profiles is null)
+            {
+                return null;
+            }
+
+            var found = profiles.TryGetValue(launchProfileName, out var launchProfile);
+            if (!found && throwIfNotFound)
+            {
+                var message = string.Format(CultureInfo.InvariantCulture, Resources.LaunchSettingsFileDoesNotContainProfileExceptionMessage, launchProfileName);
+                throw new DistributedApplicationException(message);
+            }
 
-        var found = profiles.TryGetValue(launchProfileName, out var launchProfile);
-        if (!found && throwIfNotFound)
+            return launchProfile is not null ? new (launchProfileName, launchProfile) : default;
+        }
+        catch (JsonException ex)
         {
-            var message = string.Format(CultureInfo.InvariantCulture, Resources.LaunchSettingsFileDoesNotContainProfileExceptionMessage, launchProfileName);
-            throw new DistributedApplicationException(message);
+            var metadata = projectResource.GetProjectMetadata();
+            var projectFileInfo = new FileInfo(metadata.ProjectPath);
+            var launchSettingsFilePath = Path.Combine(projectFileInfo.DirectoryName!, "Properties", "launchSettings.json");
+            var message = $"Failed to get effective launch profile for project resource '{projectResource.Name}'. There is malformed JSON in the project's launch settings file at '{launchSettingsFilePath}'.";
+            throw new DistributedApplicationException(message, ex);
         }
-
-        return launchProfile is not null ? new (launchProfileName, launchProfile) : default;
     }
 
     private static LaunchSettings? GetLaunchSettings(this IProjectMetadata projectMetadata)

tests/Aspire.Hosting.Tests/ProjectResourceTests.cs

@@ -14,6 +14,47 @@ namespace Aspire.Hosting.Tests;
 
 public class ProjectResourceTests
 {
+    [Fact]
+    public async Task AddProjectWithInvalidLaunchSettingsShouldThrowSpecificError()
+    {
+        var projectDetails = await PrepareProjectWithMalformedLaunchSettingsAsync();
+
+        var ex = Assert.Throws<DistributedApplicationException>(() =>
+        {
+            var appBuilder = CreateBuilder();
+            appBuilder.AddProject("project", projectDetails.ProjectFilePath);
+        });
+
+        var expectedMessage = $"Failed to get effective launch profile for project resource 'project'. There is malformed JSON in the project's launch settings file at '{projectDetails.LaunchSettingsFilePath}'.";
+        Assert.Equal(expectedMessage, ex.Message);
+
+        async static Task<(string ProjectFilePath, string LaunchSettingsFilePath)> PrepareProjectWithMalformedLaunchSettingsAsync()
+        {
+            var csProjContent = """
+                                <Project Sdk="Microsoft.NET.Sdk.Web">
+                                <!-- Not a real project, just a stub for testing -->
+                                </Project>
+                                """;
+
+            var launchSettingsContent = """
+                                        this { is } { mal formed! >
+                                        """;
+
+            var projectDirectoryPath = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName());
+            var projectFilePath = Path.Combine(projectDirectoryPath, "Project.csproj");
+            var propertiesDirectoryPath = Path.Combine(projectDirectoryPath, "Properties");
+            var launchSettingsFilePath = Path.Combine(propertiesDirectoryPath, "launchSettings.json");
+
+            Directory.CreateDirectory(projectDirectoryPath);
+            await File.WriteAllTextAsync(projectFilePath, csProjContent);
+
+            Directory.CreateDirectory(propertiesDirectoryPath);
+            await File.WriteAllTextAsync(launchSettingsFilePath, launchSettingsContent);
+
+            return (projectFilePath, launchSettingsFilePath);
+        }
+    }
+
     [Fact]
     public async Task AddProjectAddsEnvironmentVariablesAndServiceMetadata()
     {