Fix TypeScript AppHost package manager detection

src/Aspire.Cli/Projects/GuestAppHostProject.cs

@@ -1385,7 +1385,7 @@ private async Task EnsureRuntimeCreatedAsync(
             var runtimeSpec = await rpcClient.GetRuntimeSpecAsync(_resolvedLanguage.LanguageId, cancellationToken);
             if (TypeScriptAppHostToolchainResolver.IsTypeScriptLanguage(_resolvedLanguage))
             {
-                var toolchain = TypeScriptAppHostToolchainResolver.Resolve(directory);
+                var toolchain = TypeScriptAppHostToolchainResolver.Resolve(directory, _logger);
                 runtimeSpec = TypeScriptAppHostToolchainResolver.ApplyToRuntimeSpec(runtimeSpec, toolchain);
             }
 

src/Aspire.Cli/Projects/TypeScriptAppHostToolchainResolver.cs

@@ -6,6 +6,7 @@
 using System.Text.Json.Nodes;
 using Aspire.Cli.Utils;
 using Aspire.TypeSystem;
+using Microsoft.Extensions.Logging;
 
 namespace Aspire.Cli.Projects;
 
@@ -19,14 +20,12 @@ internal enum TypeScriptAppHostToolchain
 
 internal static class TypeScriptAppHostToolchainResolver
 {
-    internal const int MaxParentSearchDepth = 8;
-
     private const string PackageJsonFileName = "package.json";
     private const string BunLockFileName = "bun.lock";
     private const string BunBinaryLockFileName = "bun.lockb";
     private const string YarnLockFileName = "yarn.lock";
     private const string YarnConfigFileName = ".yarnrc.yml";
-    private const string YarnDirectoryName = ".yarn";
+    private const string PackageLockFileName = "package-lock.json";
     private const string PnpmLockFileName = "pnpm-lock.yaml";
 
     public static bool IsTypeScriptLanguage(LanguageInfo? language)
@@ -36,35 +35,58 @@ public static bool IsTypeScriptLanguage(LanguageInfo? language)
              language.LanguageId.Value.Equals(KnownLanguageId.TypeScriptAlias, StringComparison.OrdinalIgnoreCase));
     }
 
-    public static TypeScriptAppHostToolchain Resolve(DirectoryInfo appHostDirectory)
+    public static TypeScriptAppHostToolchain Resolve(DirectoryInfo appHostDirectory, ILogger? logger)
+    {
+        var resolution = ResolveWithReason(appHostDirectory);
+        logger?.LogDebug(
+            "Selected TypeScript AppHost package manager '{PackageManager}' because {Reason}.",
+            GetCommandName(resolution.Toolchain),
+            resolution.Reason);
+
+        return resolution.Toolchain;
+    }
+
+    internal static TypeScriptAppHostToolchainResolution ResolveWithReason(DirectoryInfo appHostDirectory)
     {
         foreach (var candidateDirectory in EnumerateCandidateDirectories(appHostDirectory))
         {
-            if (TryGetToolchainFromPackageJson(candidateDirectory, out var configuredToolchain))
+            if (TryGetToolchainFromPackageJson(candidateDirectory, out var configuredToolchain, out var reason))
+            {
+                return new(configuredToolchain, reason);
+            }
+
+            if (File.Exists(Path.Combine(candidateDirectory.FullName, BunLockFileName)))
             {
-                return configuredToolchain;
+                return CreateLockFileResolution(TypeScriptAppHostToolchain.Bun, BunLockFileName, candidateDirectory);
             }
 
-            if (File.Exists(Path.Combine(candidateDirectory.FullName, BunLockFileName)) ||
-                File.Exists(Path.Combine(candidateDirectory.FullName, BunBinaryLockFileName)))
+            if (File.Exists(Path.Combine(candidateDirectory.FullName, BunBinaryLockFileName)))
             {
-                return TypeScriptAppHostToolchain.Bun;
+                return CreateLockFileResolution(TypeScriptAppHostToolchain.Bun, BunBinaryLockFileName, candidateDirectory);
             }
 
             if (File.Exists(Path.Combine(candidateDirectory.FullName, PnpmLockFileName)))
             {
-                return TypeScriptAppHostToolchain.Pnpm;
+                return CreateLockFileResolution(TypeScriptAppHostToolchain.Pnpm, PnpmLockFileName, candidateDirectory);
             }
 
-            if (File.Exists(Path.Combine(candidateDirectory.FullName, YarnLockFileName)) ||
-                File.Exists(Path.Combine(candidateDirectory.FullName, YarnConfigFileName)) ||
-                Directory.Exists(Path.Combine(candidateDirectory.FullName, YarnDirectoryName)))
+            if (File.Exists(Path.Combine(candidateDirectory.FullName, YarnLockFileName)))
             {
-                return TypeScriptAppHostToolchain.Yarn;
+                return CreateLockFileResolution(TypeScriptAppHostToolchain.Yarn, YarnLockFileName, candidateDirectory);
+            }
+
+            if (File.Exists(Path.Combine(candidateDirectory.FullName, YarnConfigFileName)))
+            {
+                return CreateLockFileResolution(TypeScriptAppHostToolchain.Yarn, YarnConfigFileName, candidateDirectory);
+            }
+
+            if (File.Exists(Path.Combine(candidateDirectory.FullName, PackageLockFileName)))
+            {
+                return CreateLockFileResolution(TypeScriptAppHostToolchain.Npm, PackageLockFileName, candidateDirectory);
             }
         }
 
-        return TypeScriptAppHostToolchain.Npm;
+        return new(TypeScriptAppHostToolchain.Npm, $"no package manager marker found in {appHostDirectory.FullName} or an eligible parent directory");
     }
 
     public static string[] GetRequiredCommands(TypeScriptAppHostToolchain toolchain)
@@ -219,12 +241,15 @@ private static string GetTsConfigFileName(RuntimeSpec runtimeSpec)
         return "tsconfig.apphost.json";
     }
 
-    private static bool TryGetToolchainFromPackageJson(DirectoryInfo appHostDirectory, out TypeScriptAppHostToolchain toolchain)
+    private static bool TryGetToolchainFromPackageJson(DirectoryInfo appHostDirectory, out TypeScriptAppHostToolchain toolchain, out string reason)
     {
+        toolchain = default;
+        reason = string.Empty;
+
         var packageJsonPath = Path.Combine(appHostDirectory.FullName, PackageJsonFileName);
         if (!File.Exists(packageJsonPath))
         {
-            return SetUnknownToolchain(out toolchain);
+            return false;
         }
 
         try
@@ -234,17 +259,23 @@ private static bool TryGetToolchainFromPackageJson(DirectoryInfo appHostDirector
                 !packageManagerValue.TryGetValue<string>(out var packageManager) ||
                 string.IsNullOrWhiteSpace(packageManager))
             {
-                return SetUnknownToolchain(out toolchain);
+                return false;
             }
 
             var packageManagerName = packageManager.Split('@', 2)[0];
-            return TryParseToolchain(packageManagerName, out toolchain);
+            if (TryParseToolchain(packageManagerName, out toolchain))
+            {
+                reason = $"packageManager '{packageManager}' found in {packageJsonPath}";
+                return true;
+            }
+
+            return false;
         }
         catch (Exception ex) when (ex is JsonException or IOException
             or UnauthorizedAccessException or SecurityException
             or NotSupportedException)
         {
-            return SetUnknownToolchain(out toolchain);
+            return false;
         }
     }
 
@@ -265,19 +296,40 @@ private static bool TryParseToolchain(string packageManagerName, out TypeScriptA
 
     private static IEnumerable<DirectoryInfo> EnumerateCandidateDirectories(DirectoryInfo appHostDirectory)
     {
-        // Allow nested AppHosts to pick up workspace-level lockfiles/packageManager settings
-        // without accidentally walking all the way to an unrelated parent directory.
-        var currentDirectory = appHostDirectory;
-        for (var depth = 0; currentDirectory is not null && depth <= MaxParentSearchDepth; depth++)
+        yield return appHostDirectory;
+
+        // Only use the immediate parent as a fallback so a project folder can provide
+        // workspace-level hints without inheriting unrelated markers from higher directories.
+        var parentDirectory = appHostDirectory.Parent;
+        if (parentDirectory is not null && ShouldSearchParentDirectory(parentDirectory))
         {
-            yield return currentDirectory;
-            currentDirectory = currentDirectory.Parent;
+            yield return parentDirectory;
         }
     }
 
-    private static bool SetUnknownToolchain(out TypeScriptAppHostToolchain toolchain)
+    internal static bool ShouldSearchParentDirectory(DirectoryInfo parentDirectory, string? homeDirectory = null)
     {
-        toolchain = default;
-        return false;
+        var pathComparison = OperatingSystem.IsWindows() || OperatingSystem.IsMacOS()
+            ? StringComparison.OrdinalIgnoreCase
+            : StringComparison.Ordinal;
+
+        // Root and home directories are not project folders. They can contain unrelated user-level
+        // files, so package manager markers there should not influence TypeScript AppHost projects.
+        var parentPath = Path.TrimEndingDirectorySeparator(parentDirectory.FullName);
+        if (string.Equals(parentPath, Path.TrimEndingDirectorySeparator(parentDirectory.Root.FullName), pathComparison))
+        {
+            return false;
+        }
+
+        homeDirectory ??= Environment.GetFolderPath(Environment.SpecialFolder.UserProfile);
+        return string.IsNullOrWhiteSpace(homeDirectory) ||
+            !string.Equals(parentPath, Path.TrimEndingDirectorySeparator(Path.GetFullPath(homeDirectory)), pathComparison);
+    }
+
+    private static TypeScriptAppHostToolchainResolution CreateLockFileResolution(TypeScriptAppHostToolchain toolchain, string markerName, DirectoryInfo directory)
+    {
+        return new(toolchain, $"{markerName} found in {directory.FullName}");
     }
 }
+
+internal readonly record struct TypeScriptAppHostToolchainResolution(TypeScriptAppHostToolchain Toolchain, string Reason);

src/Aspire.Cli/Scaffolding/ScaffoldingService.cs

@@ -181,7 +181,7 @@ private async Task<int> InstallDependenciesAsync(
         var runtimeSpec = await rpcClient.GetRuntimeSpecAsync(language.LanguageId.Value, cancellationToken);
         if (TypeScriptAppHostToolchainResolver.IsTypeScriptLanguage(language))
         {
-            var toolchain = TypeScriptAppHostToolchainResolver.Resolve(directory);
+            var toolchain = TypeScriptAppHostToolchainResolver.Resolve(directory, _logger);
             runtimeSpec = TypeScriptAppHostToolchainResolver.ApplyToRuntimeSpec(runtimeSpec, toolchain);
         }
 
@@ -280,14 +280,14 @@ private static bool IsTypeScriptLanguage(LanguageInfo language)
             language.LanguageId.Value.Equals(KnownLanguageId.TypeScriptAlias, StringComparison.OrdinalIgnoreCase);
     }
 
-    private static string GetPackageManagerCommand(DirectoryInfo directory, LanguageInfo language)
+    private string GetPackageManagerCommand(DirectoryInfo directory, LanguageInfo language)
     {
         if (!TypeScriptAppHostToolchainResolver.IsTypeScriptLanguage(language))
         {
             return "npm";
         }
 
-        var toolchain = TypeScriptAppHostToolchainResolver.Resolve(directory);
+        var toolchain = TypeScriptAppHostToolchainResolver.Resolve(directory, _logger);
         return TypeScriptAppHostToolchainResolver.GetCommandName(toolchain);
     }
 }

src/Aspire.Cli/Utils/EnvironmentChecker/TypeScriptAppHostToolingCheck.cs

@@ -48,7 +48,7 @@ public async Task<IReadOnlyList<EnvironmentCheckResult>> CheckAsync(Cancellation
             return [];
         }
 
-        var toolchain = TypeScriptAppHostToolchainResolver.Resolve(appHostDirectory);
+        var toolchain = TypeScriptAppHostToolchainResolver.Resolve(appHostDirectory, _logger);
         var missingResults = new List<EnvironmentCheckResult>();
 
         foreach (var command in TypeScriptAppHostToolchainResolver.GetRequiredCommands(toolchain))

src/Aspire.Cli/Utils/MissingJavaScriptToolWarning.cs

@@ -41,7 +41,7 @@ private static (string InstallCommand, string InstallDisplayName) GetMessagePart
     {
         if (TypeScriptAppHostToolchainResolver.IsTypeScriptLanguage(language))
         {
-            var toolchain = TypeScriptAppHostToolchainResolver.Resolve(directory);
+            var toolchain = TypeScriptAppHostToolchainResolver.Resolve(directory, logger: null);
             return (TypeScriptAppHostToolchainResolver.GetInstallCommand(toolchain), TypeScriptAppHostToolchainResolver.GetDisplayName(toolchain));
         }