Add a flag to hostfxr_resolve_sdk2_flags_t to silence error messages

[jtschuster]

See dotnet/sdk#50632 for context.

hostfxr_resolve_sdk2 will print error messages to stderr by default. We can add a flag to the enum to allow for silencing these errors when we want to try to resolve an sdk, but a failure to resolve shouldn't be surfaced to the console.

Alternatives:

• Add a callback parameter for error messages the way we do for returning result paths. This could have a default to print to stderr and still be reasonable to backport.
• Add a new boolean parameter to silence warnings. I think flags make more sense, especially since there's already a flags parameter.
• Add a new API that only gets global.json information.

[Copilot]

Pull Request Overview

This PR adds a do_not_print_errors flag to the hostfxr_resolve_sdk2 API to allow callers to suppress error messages when SDK resolution fails. This enables scenarios where SDK resolution is attempted but failures should not be surfaced to the console.

Key Changes:

• Added a new do_not_print_errors flag (0x2) to the hostfxr_resolve_sdk2_flags_t enum
• Modified the SDK resolver to respect this flag when printing error messages
• Added comprehensive tests to verify the flag behavior in both success and failure scenarios

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/native/corehost/fxr/hostfxr.cpp	Added do_not_print_errors flag to enum and passed it to the SDK resolver
src/installer/tests/HostActivation.Tests/NativeHostApis.cs	Added test cases to verify the new flag works correctly
src/installer/tests/Assets/Projects/HostApiInvokerApp/HostFXR.cs	Added do_not_print_errors flag to the C# enum definition
docs/design/features/hosting-layer-apis.md	Updated API documentation to include the new flag

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[Copilot]

Pull Request Overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.

[marcpopMSFT]

Do we know why hostfxr is reporting errors in 50632? In those cases, the SDK is actually found by the host so it feels like the primary bug is that the ResolveSdk api is failing (and secondarily, we don't want duplicate errors from the resolvesdk call and the host when the sdk truly can't be found). We actually don't call that api anywhere else in the SDK from .net core (we do call it in VS from teh resolver running in .net framework_). Everywhere else in core, we call GetAvailableSdks.

[jtschuster]

I think it's expected that sdk resolution always fails in that call in the sdk. It's passing an empty string as the dotnet_exe argument and only is trying to get the global.json state.

[sbomer]

Implementation LGTM as someone not familiar with the host. I wonder if there's a way to avoid introducing a new public flag, but this makes sense to me given the way the telemetry is currently implemented. I don't have context to tell whether that could easily be changed (for example to only emit the global.json telemetry when actually doing the SDK resolution).

[jtschuster]

/backport to release/10.0

[github-actions]

Started backporting to release/10.0: https://github.com/dotnet/runtime/actions/runs/17748919764