Add fallback parsing support for single-file apphost projects (#12197)

* Initial plan

* Add fallback parsing for single-file apphost projects

Implemented regex-based parsing for .cs single-file apphost files in FallbackProjectParser to extract SDK and package directives when MSBuild evaluation fails.

Co-authored-by: mitchdenny <[email protected]>

* Address code review feedback - extract regex patterns as constants

Co-authored-by: mitchdenny <[email protected]>

* Convert regex patterns to source-generated regex

Co-authored-by: mitchdenny <[email protected]>

* Move fallback parsing warning to resource strings and make message generic

- Added FallbackParsingWarning to UpdateCommandStrings.resx
- Updated ProjectUpdater to use resource string instead of hardcoded message
- Renamed FallbackXmlParsing property to FallbackParsing for generality
- Updated log messages to remove "XML" references since parsing now supports both XML and C# files

Co-authored-by: mitchdenny <[email protected]>

* Use Directory.CreateTempSubdirectory instead of Path.GetTempPath in tests

Updated all FallbackProjectParserTests to use Directory.CreateTempSubdirectory() for better test isolation and cleanup. Each test now creates its own temporary subdirectory and cleans it up in a finally block.

Co-authored-by: davidfowl <[email protected]>

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: mitchdenny <[email protected]>
Co-authored-by: davidfowl <[email protected]>

Author: 3 people

src/Aspire.Cli/Projects/FallbackProjectParser.cs

@@ -3,97 +3,160 @@
 
 using System.Text.Json;
 using System.Text.Json.Nodes;
+using System.Text.RegularExpressions;
 using System.Xml.Linq;
 using Microsoft.Extensions.Logging;
 
 namespace Aspire.Cli.Projects;
 
 /// <summary>
-/// Provides fallback XML parsing capabilities when MSBuild evaluation fails.
+/// Provides fallback parsing capabilities when MSBuild evaluation fails.
+/// Supports both .csproj XML files and .cs single-file apphost files.
 /// Used primarily for AppHost projects with unresolvable SDK versions.
 /// </summary>
-internal sealed class FallbackProjectParser
+internal sealed partial class FallbackProjectParser
 {
     private readonly ILogger<FallbackProjectParser> _logger;
 
+    [GeneratedRegex(@"#:sdk\s+Aspire\.AppHost\.Sdk@([\d\.\-a-zA-Z]+|\*)")]
+    private static partial Regex SdkDirectiveRegex();
+
+    [GeneratedRegex(@"#:package\s+([a-zA-Z0-9\._]+)@([\d\.\-a-zA-Z]+|\*)")]
+    private static partial Regex PackageDirectiveRegex();
+
     public FallbackProjectParser(ILogger<FallbackProjectParser> logger)
     {
         _logger = logger;
     }
 
     /// <summary>
-    /// Parses a project file using direct XML parsing to extract basic project information.
+    /// Parses a project file using direct parsing to extract basic project information.
     /// Returns a synthetic JsonDocument that mimics MSBuild's GetProjectItemsAndProperties output.
+    /// Supports both .csproj XML files and .cs single-file apphost files.
     /// </summary>
     public JsonDocument ParseProject(FileInfo projectFile)
     {
         try
         {
-            _logger.LogDebug("Parsing project file '{ProjectFile}' using fallback XML parser", projectFile.FullName);
-
-            var doc = XDocument.Load(projectFile.FullName);
-            var root = doc.Root;
+            _logger.LogDebug("Parsing project file '{ProjectFile}' using fallback parser", projectFile.FullName);
 
-            if (root?.Name.LocalName != "Project")
+            // Detect file type and route to appropriate parser
+            if (string.Equals(projectFile.Extension, ".csproj", StringComparison.OrdinalIgnoreCase))
             {
-                throw new InvalidOperationException($"Invalid project file format: {projectFile.FullName}");
+                return ParseCsprojProjectFile(projectFile);
             }
-
-            // Extract SDK information
-            var aspireHostingSdkVersion = ExtractAspireHostingSdkVersion(root);
-
-            // Extract package references
-            var packageReferences = ExtractPackageReferences(root);
-
-            // Extract project references
-            var projectReferences = ExtractProjectReferences(root, projectFile);
-
-            // Build the synthetic JSON structure using JsonObject
-            var rootObject = new JsonObject();
-            
-            // Items section
-            var itemsObject = new JsonObject();
-            
-            // PackageReference items
-            var packageRefArray = new JsonArray();
-            foreach (var pkg in packageReferences)
+            else if (string.Equals(projectFile.Extension, ".cs", StringComparison.OrdinalIgnoreCase))
             {
-                var packageObj = new JsonObject();
-                packageObj["Identity"] = JsonValue.Create(pkg.Identity);
-                packageObj["Version"] = JsonValue.Create(pkg.Version);
-                packageRefArray.Add((JsonNode?)packageObj);
+                return ParseCsAppHostFile(projectFile);
             }
-            itemsObject["PackageReference"] = packageRefArray;
-            
-            // ProjectReference items
-            var projectRefArray = new JsonArray();
-            foreach (var proj in projectReferences)
+            else
             {
-                var projectObj = new JsonObject();
-                projectObj["Identity"] = JsonValue.Create(proj.Identity);
-                projectObj["FullPath"] = JsonValue.Create(proj.FullPath);
-                projectRefArray.Add((JsonNode?)projectObj);
+                throw new ProjectUpdaterException($"Unsupported project file type: {projectFile.Extension}. Expected .csproj or .cs file.");
             }
-            itemsObject["ProjectReference"] = projectRefArray;
-            
-            rootObject["Items"] = itemsObject;
-            
-            // Properties section
-            var propertiesObject = new JsonObject();
-            propertiesObject["AspireHostingSDKVersion"] = JsonValue.Create(aspireHostingSdkVersion);
-            rootObject["Properties"] = propertiesObject;
-            
-            // Fallback flag
-            rootObject["Fallback"] = JsonValue.Create(true);
-
-            // Convert JsonObject to JsonDocument
-            return JsonDocument.Parse(rootObject.ToJsonString());
+        }
+        catch (ProjectUpdaterException)
+        {
+            // Re-throw our custom exceptions
+            throw;
         }
         catch (Exception ex)
         {
-            _logger.LogError(ex, "Failed to parse project file '{ProjectFile}' using fallback XML parser", projectFile.FullName);
-            throw new ProjectUpdaterException($"Failed to parse project file '{projectFile.FullName}' using fallback XML parser: {ex.Message}", ex);
+            _logger.LogError(ex, "Failed to parse project file '{ProjectFile}' using fallback parser", projectFile.FullName);
+            throw new ProjectUpdaterException($"Failed to parse project file '{projectFile.FullName}' using fallback parser: {ex.Message}", ex);
+        }
+    }
+
+    /// <summary>
+    /// Parses a .csproj XML project file to extract SDK and package information.
+    /// </summary>
+    private static JsonDocument ParseCsprojProjectFile(FileInfo projectFile)
+    {
+        var doc = XDocument.Load(projectFile.FullName);
+        var root = doc.Root;
+
+        if (root?.Name.LocalName != "Project")
+        {
+            throw new InvalidOperationException($"Invalid project file format: {projectFile.FullName}");
         }
+
+        // Extract SDK information
+        var aspireHostingSdkVersion = ExtractAspireHostingSdkVersion(root);
+
+        // Extract package references
+        var packageReferences = ExtractPackageReferences(root);
+
+        // Extract project references
+        var projectReferences = ExtractProjectReferences(root, projectFile);
+
+        return BuildJsonDocument(aspireHostingSdkVersion, packageReferences, projectReferences);
+    }
+
+    /// <summary>
+    /// Parses a .cs single-file apphost to extract SDK and package information from directives.
+    /// </summary>
+    private static JsonDocument ParseCsAppHostFile(FileInfo projectFile)
+    {
+        var fileContent = File.ReadAllText(projectFile.FullName);
+
+        // Extract SDK version from #:sdk directive
+        var aspireHostingSdkVersion = ExtractSdkVersionFromDirective(fileContent);
+
+        // Extract package references from #:package directives
+        var packageReferences = ExtractPackageReferencesFromDirectives(fileContent);
+
+        // Single-file apphost projects don't have project references
+        var projectReferences = Array.Empty<ProjectReferenceInfo>();
+
+        return BuildJsonDocument(aspireHostingSdkVersion, packageReferences, projectReferences);
+    }
+
+    /// <summary>
+    /// Builds a synthetic JsonDocument from extracted project information.
+    /// </summary>
+    private static JsonDocument BuildJsonDocument(
+        string? aspireHostingSdkVersion,
+        PackageReferenceInfo[] packageReferences,
+        ProjectReferenceInfo[] projectReferences)
+    {
+        var rootObject = new JsonObject();
+        
+        // Items section
+        var itemsObject = new JsonObject();
+        
+        // PackageReference items
+        var packageRefArray = new JsonArray();
+        foreach (var pkg in packageReferences)
+        {
+            var packageObj = new JsonObject();
+            packageObj["Identity"] = JsonValue.Create(pkg.Identity);
+            packageObj["Version"] = JsonValue.Create(pkg.Version);
+            packageRefArray.Add((JsonNode?)packageObj);
+        }
+        itemsObject["PackageReference"] = packageRefArray;
+        
+        // ProjectReference items
+        var projectRefArray = new JsonArray();
+        foreach (var proj in projectReferences)
+        {
+            var projectObj = new JsonObject();
+            projectObj["Identity"] = JsonValue.Create(proj.Identity);
+            projectObj["FullPath"] = JsonValue.Create(proj.FullPath);
+            projectRefArray.Add((JsonNode?)projectObj);
+        }
+        itemsObject["ProjectReference"] = projectRefArray;
+        
+        rootObject["Items"] = itemsObject;
+        
+        // Properties section
+        var propertiesObject = new JsonObject();
+        propertiesObject["AspireHostingSDKVersion"] = JsonValue.Create(aspireHostingSdkVersion);
+        rootObject["Properties"] = propertiesObject;
+        
+        // Fallback flag
+        rootObject["Fallback"] = JsonValue.Create(true);
+
+        // Convert JsonObject to JsonDocument
+        return JsonDocument.Parse(rootObject.ToJsonString());
     }
 
     private static string? ExtractAspireHostingSdkVersion(XElement projectRoot)
@@ -172,6 +235,51 @@ private static ProjectReferenceInfo[] ExtractProjectReferences(XElement projectR
 
         return projectReferences.ToArray();
     }
+
+    /// <summary>
+    /// Extracts the Aspire.AppHost.Sdk version from the #:sdk directive in a single-file apphost.
+    /// </summary>
+    private static string? ExtractSdkVersionFromDirective(string fileContent)
+    {
+        // Match: #:sdk Aspire.AppHost.Sdk@<version>
+        // Where version can be a semantic version or wildcard (*)
+        var match = SdkDirectiveRegex().Match(fileContent);
+        
+        if (match.Success)
+        {
+            return match.Groups[1].Value;
+        }
+
+        return null;
+    }
+
+    /// <summary>
+    /// Extracts package references from #:package directives in a single-file apphost.
+    /// </summary>
+    private static PackageReferenceInfo[] ExtractPackageReferencesFromDirectives(string fileContent)
+    {
+        var packageReferences = new List<PackageReferenceInfo>();
+
+        // Match: #:package <PackageId>@<version>
+        // Where version can be a semantic version or wildcard (*)
+        var matches = PackageDirectiveRegex().Matches(fileContent);
+
+        foreach (Match match in matches)
+        {
+            var identity = match.Groups[1].Value;
+            var version = match.Groups[2].Value;
+
+            var packageRef = new PackageReferenceInfo
+            {
+                Identity = identity,
+                Version = version
+            };
+
+            packageReferences.Add(packageRef);
+        }
+
+        return packageReferences.ToArray();
+    }
 }
 
 internal record PackageReferenceInfo

src/Aspire.Cli/Projects/ProjectUpdater.cs

@@ -63,10 +63,10 @@ public async Task<ProjectUpdateResult> UpdateProjectAsync(FileInfo projectFile,
             interactionService.DisplayEmptyLine();
         }
 
-        // Display warning if fallback XML parsing was used
+        // Display warning if fallback parsing was used
         if (fallbackUsed)
         {
-            interactionService.DisplayMessage("warning", "[yellow]Note: Update plan generated using fallback XML parsing due to unresolvable AppHost SDK. Dependency analysis may have reduced accuracy.[/]");
+            interactionService.DisplayMessage("warning", $"[yellow]{UpdateCommandStrings.FallbackParsingWarning}[/]");
             interactionService.DisplayEmptyLine();
         }
 
@@ -157,7 +157,7 @@ private static bool IsGlobalNuGetConfig(string path)
             await analyzeStep.Callback();
         }
 
-        return (context.UpdateSteps, context.FallbackXmlParsing);
+        return (context.UpdateSteps, context.FallbackParsing);
     }
 
     private const string ItemsAndPropertiesCacheKeyPrefix = "ItemsAndProperties";
@@ -202,12 +202,12 @@ private async Task<JsonDocument> GetItemsAndPropertiesWithFallbackAsync(FileInfo
         catch (ProjectUpdaterException ex) when (IsAppHostProject(projectFile, context))
         {
             // Only use fallback for AppHost projects
-            logger.LogWarning("Falling back to XML parsing for '{ProjectFile}'. Reason: {Message}", projectFile.FullName, ex.Message);
+            logger.LogWarning("Falling back to parsing for '{ProjectFile}'. Reason: {Message}", projectFile.FullName, ex.Message);
 
-            if (!context.FallbackXmlParsing)
+            if (!context.FallbackParsing)
             {
-                context.FallbackXmlParsing = true;
-                logger.LogWarning("Update plan will be generated using fallback XML parsing; dependency accuracy may be reduced.");
+                context.FallbackParsing = true;
+                logger.LogWarning("Update plan will be generated using fallback parsing; dependency accuracy may be reduced.");
             }
 
             return fallbackParser.ParseProject(projectFile);
@@ -863,7 +863,7 @@ internal sealed class UpdateContext(FileInfo appHostProjectFile, PackageChannel
     public ConcurrentQueue<UpdateStep> UpdateSteps { get; } = new();
     public ConcurrentQueue<AnalyzeStep> AnalyzeSteps { get; } = new();
     public HashSet<string> VisitedProjects { get; } = new();
-    public bool FallbackXmlParsing { get; set; }
+    public bool FallbackParsing { get; set; }
 }
 
 internal abstract record UpdateStep(string Description, Func<Task> Callback)

src/Aspire.Cli/Resources/UpdateCommandStrings.Designer.cs

@@ -111,4 +111,7 @@
   <data name="MappingRetainedFormat" xml:space="preserve">
     <value>   Mapping: {0}</value>
   </data>
+  <data name="FallbackParsingWarning" xml:space="preserve">
+    <value>Note: Update plan generated using fallback parsing due to unresolvable AppHost SDK. Dependency analysis may have reduced accuracy.</value>
+  </data>
 </root>