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Make SDK resolution error messages more helpful. #341

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Merged
merged 2 commits into from
Oct 2, 2025
Merged

Make SDK resolution error messages more helpful. #341

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a407fae
Make SDK resolution error messages more helpful.
teo-tsirpanis Oct 1, 2025
143d86f
Shorten exception message.
teo-tsirpanis Oct 2, 2025
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18 changes: 12 additions & 6 deletions src/MSBuildLocator/DotNetSdkLocationHelper.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@
using System.Reflection;
using System.Runtime.InteropServices;
using System.Runtime.Loader;
using System.Text;
using System.Text.RegularExpressions;

#nullable enable
Expand Down Expand Up @@ -117,11 +118,13 @@ public static IEnumerable<VisualStudioInstance> GetInstances(string workingDirec
static IEnumerable<string> GetAllAvailableSDKs(bool allowAllDotnetLocations)
{
bool foundSdks = false;
int rc = 0;
StringBuilder? errorMessage = null;
foreach (string dotnetPath in s_dotnetPathCandidates.Value)
{
int rc = NativeMethods.hostfxr_get_available_sdks(exe_dir: dotnetPath, out string[]? resolvedPaths);
rc = NativeMethods.hostfxr_get_available_sdks(exe_dir: dotnetPath, out string[]? resolvedPaths, out errorMessage);

if (rc == 0 && resolvedPaths != null)
if (resolvedPaths != null)
{
foundSdks = true;

Expand All @@ -140,17 +143,19 @@ static IEnumerable<string> GetAllAvailableSDKs(bool allowAllDotnetLocations)
// Errors are automatically printed to stderr. We should not continue to try to output anything if we failed.
if (!foundSdks)
{
throw new InvalidOperationException(SdkResolutionExceptionMessage(nameof(NativeMethods.hostfxr_get_available_sdks)));
throw new InvalidOperationException(SdkResolutionExceptionMessage(nameof(NativeMethods.hostfxr_get_available_sdks), rc, errorMessage));
}
}

// Determines the directory location of the SDK accounting for global.json and multi-level lookup policy.
static string? GetSdkFromGlobalSettings(string workingDirectory)
{
string? resolvedSdk = null;
int rc = 0;
StringBuilder? errorMessage = null;
foreach (string dotnetPath in s_dotnetPathCandidates.Value)
{
int rc = NativeMethods.hostfxr_resolve_sdk2(exe_dir: dotnetPath, working_dir: workingDirectory, flags: 0, out resolvedSdk, out _);
rc = NativeMethods.hostfxr_resolve_sdk2(exe_dir: dotnetPath, working_dir: workingDirectory, flags: 0, out resolvedSdk, out _, out errorMessage);

if (rc == 0)
{
Expand All @@ -160,7 +165,7 @@ static IEnumerable<string> GetAllAvailableSDKs(bool allowAllDotnetLocations)
}

return string.IsNullOrEmpty(resolvedSdk)
? throw new InvalidOperationException(SdkResolutionExceptionMessage(nameof(NativeMethods.hostfxr_resolve_sdk2)))
? throw new InvalidOperationException(SdkResolutionExceptionMessage(nameof(NativeMethods.hostfxr_resolve_sdk2), rc, errorMessage))
: resolvedSdk;
}
}
Expand Down Expand Up @@ -229,7 +234,8 @@ private static IntPtr HostFxrResolver(Assembly assembly, string libraryName)
throw new InvalidOperationException(error);
}

private static string SdkResolutionExceptionMessage(string methodName) => $"Failed to find all versions of .NET Core MSBuild. Call to {methodName}. There may be more details in stderr.";
private static string SdkResolutionExceptionMessage(string methodName, int rc, StringBuilder? errorMessage) =>
$"Error while calling hostfxr function {methodName}. Error code: {rc} Detailed error: {errorMessage}";

private static List<string> ResolveDotnetPathCandidates()
{
Expand Down
49 changes: 47 additions & 2 deletions src/MSBuildLocator/NativeMethods.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Runtime.InteropServices.Marshalling;
using System.Text;

namespace Microsoft.Build.Locator
{
Expand All @@ -25,17 +26,19 @@ private enum hostfxr_resolve_sdk2_result_key_t
global_json_path = 1,
};

internal static int hostfxr_resolve_sdk2(string exe_dir, string working_dir, hostfxr_resolve_sdk2_flags_t flags, out string resolved_sdk_dir, out string global_json_path)
internal static int hostfxr_resolve_sdk2(string exe_dir, string working_dir, hostfxr_resolve_sdk2_flags_t flags, out string resolved_sdk_dir, out string global_json_path, out StringBuilder errorMessage)
{
Debug.Assert(t_resolve_sdk2_resolved_sdk_dir is null);
Debug.Assert(t_resolve_sdk2_global_json_path is null);
try
{
unsafe
{
using var errorHandler = new ErrorHandler();
int result = hostfxr_resolve_sdk2(exe_dir, working_dir, flags, &hostfxr_resolve_sdk2_callback);
resolved_sdk_dir = t_resolve_sdk2_resolved_sdk_dir;
global_json_path = t_resolve_sdk2_global_json_path;
errorMessage = t_hostfxr_error_builder;
return result;
}
}
Expand Down Expand Up @@ -72,15 +75,17 @@ private static unsafe void hostfxr_resolve_sdk2_callback(hostfxr_resolve_sdk2_re
}
}

internal static int hostfxr_get_available_sdks(string exe_dir, out string[] sdks)
internal static int hostfxr_get_available_sdks(string exe_dir, out string[] sdks, out StringBuilder errorMessage)
{
Debug.Assert(t_get_available_sdks_result is null);
try
{
unsafe
{
using var errorHandler = new ErrorHandler();
int result = hostfxr_get_available_sdks(exe_dir, &hostfxr_get_available_sdks_callback);
sdks = t_get_available_sdks_result;
errorMessage = t_hostfxr_error_builder;
return result;
}
}
Expand Down Expand Up @@ -108,6 +113,29 @@ private static unsafe void hostfxr_get_available_sdks_callback(int count, void**
t_get_available_sdks_result = result;
}

[LibraryImport(HostFxrName)]
[UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
private static unsafe partial delegate* unmanaged[Cdecl]<void*, void> hostfxr_set_error_writer(delegate* unmanaged[Cdecl]<void*, void> error_writer);

[ThreadStatic]
private static StringBuilder t_hostfxr_error_builder;

[UnmanagedCallersOnly(CallConvs = [typeof(CallConvCdecl)])]
private static unsafe void hostfxr_error_writer_callback(void* message)
{
t_hostfxr_error_builder ??= new StringBuilder();
if (OperatingSystem.IsWindows())
{
// Avoid allocating temporary string on Windows.
t_hostfxr_error_builder.Append(MemoryMarshal.CreateReadOnlySpanFromNullTerminated((char*)message));
t_hostfxr_error_builder.AppendLine();
}
else
{
t_hostfxr_error_builder.AppendLine(Utf8StringMarshaller.ConvertToManaged((byte*)message));
}
}

[CustomMarshaller(typeof(string), MarshalMode.Default, typeof(AutoStringMarshaller))]
internal static unsafe class AutoStringMarshaller
{
Expand All @@ -117,6 +145,23 @@ internal static unsafe class AutoStringMarshaller

public static string ConvertToManaged(void* ptr) => Marshal.PtrToStringAuto((nint)ptr);
}

private unsafe readonly ref struct ErrorHandler
{
private readonly delegate* unmanaged[Cdecl]<void*, void> _previousCallback;

public ErrorHandler()
{
Debug.Assert(t_hostfxr_error_builder is null);
_previousCallback = hostfxr_set_error_writer(&hostfxr_error_writer_callback);
}

public void Dispose()
{
hostfxr_set_error_writer(_previousCallback);
t_hostfxr_error_builder = null;
}
}
}
}
#endif
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