[watch] Fixes command line parsing and TFM selection for FBAs

[tmat]

dotnet run uses the first application argument that is not -bl to find file-based app entry point. dotnet watch did not skip the options of run subcommand when parsing the command line. E.g. dotnet run -e X=1 -bl App.cs works but dotnet watch -e X=1 -bl App.cs did not.

Fixes #53598
Fixes #53718

[tmat]

@DustinCampbell @jjonescz @jonathanpeppers ptal

[Copilot]

Pull request overview

This PR fixes dotnet watch file-based app (FBA) command-line parsing so the correct entry point is discovered even when dotnet run options (like -e and -bl) are present, and adds/improves target framework selection behavior for FBAs (including multi-targeting prompts).

Changes:

• Parse dotnet watch “run” arguments using the dotnet run command definition so run-subcommand options don’t confuse entry point detection.
• Add shared directive parsing helper (VirtualProjectBuilder.GetPropertyFromSourceFile) and use it for FBA TFM selection in both dotnet run and dotnet watch.
• Add/adjust tests covering binlog stripping, FBA include directive/hotreload, and FBA TFM selection.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
test/Microsoft.NET.TestFramework/TestAssetsManager.cs	Adds helper to create an empty test asset directory for new tests.
test/dotnet-watch.Tests/HotReload/FileBasedAppTests.cs	New hot reload tests for FBA include directives and TFM selection prompting.
test/dotnet-watch.Tests/HotReload/CompilationHandlerTests.cs	Updates ProjectGraphFactory usage after signature change.
test/dotnet-watch.Tests/HotReload/BuildProjectsTests.cs	Adds unit tests covering FBA framework selection behavior during builds.
test/dotnet-watch.Tests/CommandLine/ProgramTests.GetProjectOptions.cs	Adds regression coverage for -bl/-e not breaking FBA entry point detection.
test/dotnet-watch.Tests/CommandLine/CommandLineOptionsTests.cs	Updates tests for Command type change and binlog stripping behavior.
test/dotnet-watch.Tests/Build/ProjectGraphFactoryTests.cs	Updates tests to new TryLoadProjectGraph signature.
src/Microsoft.DotNet.ProjectTools/VirtualProjectBuilder.cs	Introduces a shared helper to read #:property values from source directives.
src/Microsoft.DotNet.ProjectTools/PublicAPI.Unshipped.txt	Records the newly added public API surface.
src/Dotnet.Watch/Watch/HotReload/HotReloadDotNetWatcher.cs	Implements FBA directive-based TFM selection and threads virtual-project TFM into graph loading.
src/Dotnet.Watch/Watch/Build/ProjectGraphFactory.cs	Moves virtual-project TFM from constructor to per-call parameter.
src/Dotnet.Watch/dotnet-watch/Watch/MsBuildFileSetFactory.cs	Updates graph loading call to pass virtual-project TFM.
src/Dotnet.Watch/dotnet-watch/Program.cs	Fixes FBA entry point detection by parsing args with RunCommandDefinition.
src/Dotnet.Watch/dotnet-watch/CommandLine/CommandLineOptions.cs	Changes Command to System.CommandLine.Command and adds binlog-stripped args list.
src/Cli/dotnet/Commands/Run/RunCommand.cs	Uses the shared directive helper for multi-target FBA framework selection.

[jonathanpeppers]

The changes here make sense to me, but they would mostly apply to console apps with TargetFrameworks set -- seems like a rare use-case.

I don't see how we could make file-based .NET MAUI apps work anytime soon -- both iOS and Android require multiple files (app icons, manifests), we'd have to generate "default" ones in obj -- no plans to do that at the moment.

[tmat]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[DustinCampbell]

tiny nit: extra blank line

[tmat]

/ba-g Known unrelated test issues:

● All test failures in PR #53698 are already tracked by existing issues:

1. ✅ C++/CLI tests (8 failures across Microsoft.NET.Build.Tests.dll.4, .dll.16)

Tracked by #53789 (#53789) — C++/CLI tests fail on VS 2026 Helix machines -
MSB8020 v143 platform toolset not found

The VS 2026 scout images only have v180 toolset, but the .vcxproj test assets target v143 (VS 2022). Affects all of:

• SourceLinkTests.Cpp
• GivenThatWeWantToBuildACppCliProject.* (all methods)
• GivenThatWeWantToBuildACppCliProjectWithTransitiveDeps.* (all methods)
• GivenThatWeWantToPublishACppCliProject.When_referenced_by_csharp_project_it_publishes_and_runs

2. ✅ It_publishes_the_project_with_a_refs_folder_and_correct_deps_file (net46)

Tracked by #53796 (#53796) —
It_publishes_the_project_with_a_refs_folder_and_correct_deps_file test failure

The mscorlib.dll vs .NETFramework/v4.6/m… string mismatch in the deps file. Consistently fails in CI.

All failures in PR #53698 are known issues — none are new