Update host to use the optional localPath property when resolving assets

[elinor-fung]

Currently, when resolving RID-agnostic assets from an application itself (that is, those in the app's .deps.json), any subdirectory specified in the file path is ignored. We just take the file name and expect it to be next to the .deps.json.

#117682 added an optional localPath property for assets. If set, this represents the path on disk relative to the .deps.json. This change updates the host to consume that property. When resolving assets from an application itself:

1. localPath property is set: use <deps_dir>/<localPath>
2. asset is from a runtimepack: use <deps_dir>/<file_path>
   • runtimepack assets are always generated with the actual destination path in the file path
3. otherwise (this is the existing behaviour):
   • RID-specific assets: use <deps_dir>/<file_path>
   • RID-agnostic assets:
     • runtime: take only the file name, use <deps_dir>/<file_name>
     • resources: take parent directory name of the file path, use <deps_dir>/<dir_name>/<file_name>

Example .deps.json resolution

With the following package in a .deps.json:

"MyPackage/1.0.0": {
  "runtime": {
    // resolves to <deps_dir>/pkg/lib.dll
    "lib/net10.0/lib.dll": {
      "localPath": "pkg/lib.dll"
    },
    // resolves to <deps_dir>/lib2.dll
    "lib/net10.0/lib2.dll": { },
    "resources": {
      // resolves to <deps_dir>/pkg/fr/lib.resources.dll
      "lib/net10.0/fr/lib.resources.dll": {
        "localPath": "pkg/fr/lib.resources.dll"
      },
      // resolves to <deps_dir>/de/lib.resources.dll
      "lib/net10.0/de/lib.resources.dll": { },
    }
  },
 "runtimeTargets": {
    // resolves to <deps_dir>/pkg/runtimes/win-x64/native/libnative.dll
    "runtimes/win-x64/native/libnative.dll": {
      "localPath": "pkg/runtimes/win-x64/native/libnative.dll"
    },
    // resolves to <deps_dir>/runtimes/win-x64/native/libnative2.dll
    "runtimes/win-x64/native/libnative2.dll": { }
  }
}

The paths would be:

• TPA: <deps_dir>/pkg/lib.dll, <deps_dir>/lib2.dll
• Resource roots: <deps_dir>/pkg
• Native search directories: <deps_dir>/pkg/runtimes/win-x64/native

With this change, usage of app-relative .NET search, and some msbuild hackery, it is possible to publish a self-contained application and stick the runtimepack in a subdirectory:

<PropertyGroup>
  <AppHostRelativeDotNet>runtimepack</AppHostRelativeDotNet>
</PropertyGroup>
<Target Name="UpdateRuntimePackAssets" AfterTargets="ResolveRuntimePackAssets">
  <ItemGroup>
    <RuntimePackAsset Update="@(RuntimePackAsset)->WithMetadataValue('CopyLocal', 'true')"
      DestinationSubPath="$(AppHostRelativeDotNet)\%(FileName)%(Extension)"
      DestinationSubDirectory="$(AppHostRelativeDotNet)\" />
    <ReferenceCopyLocalPaths Remove="@(RuntimePackAsset)" />
    <ReferenceCopyLocalPaths Include="@(RuntimePackAsset)" />
  </ItemGroup>
</Target>

Resolves #3525
cc @dotnet/appmodel @AaronRobinsonMSFT

[Copilot]

Pull Request Overview

This PR implements support for the optional localPath property in .deps.json files to allow more flexible asset resolution in the .NET host. The host now uses the localPath property when available to determine the actual file location relative to the application directory, providing better control over asset placement.

Key changes:

• Updated asset resolution logic to prioritize localPath when available
• Modified path computation to handle different asset types and library types appropriately
• Added comprehensive test coverage for the new functionality

Reviewed Changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/native/corehost/hostpolicy/deps_resolver.cpp	Updated asset resolution logic to use localPath and refactored method names
src/native/corehost/hostpolicy/deps_format.cpp	Added parsing and tracing for the localPath property
src/native/corehost/hostpolicy/deps_entry.h	Added local_path field to deps_asset_t struct and updated method signatures
src/native/corehost/hostpolicy/deps_entry.cpp	Implemented new path resolution logic using localPath with fallback behavior
src/native/corehost/fxr/standalone/hostpolicy_resolver.cpp	Fixed a bug where version string was not being returned
src/installer/tests/TestUtils/NetCoreAppBuilder.cs	Added support for localPath in test infrastructure
src/installer/tests/TestUtils/DotNetBuilder.cs	Updated test builders to use new WithLocalPath method
src/installer/tests/HostActivation.Tests/SelfContainedAppLaunch.cs	Added test for custom runtime location using app-relative paths
src/installer/tests/HostActivation.Tests/DependencyResolution/ResolveComponentDependencies.cs	Updated test to use new WithLocalPath method
src/installer/tests/HostActivation.Tests/DependencyResolution/LocalPath.cs	New comprehensive test file covering all asset types with and without localPath
src/installer/tests/HostActivation.Tests/DependencyResolution/DependencyResolutionCommandResultExtensions.cs	Added helper methods for testing resource root path resolution