Null in list of warnings or errors in SDK result

src/Build/BackEnd/Components/SdkResolution/SdkResolverService.cs

@@ -372,6 +372,13 @@ private SdkResult ResolveSdkUsingAllResolvers(int submissionId, SdkReference sdk
  {
  MSBuildEventSource.Log.SdkResolverResolveSdkStart();
  result = (SdkResult)sdkResolver.Resolve(sdk, context, resultFactory);
+
+ // We have had issues, for example dotnet/msbuild/issues/9537, where the SDK resolver returned null as particular warnings or errors.
+ // Since this can be caused by custom and 3rd party SDK resolvers, we want to log this information to help diagnose the issue.
+ if (result?.Warnings?.Any(s => s is null) == true || result?.Errors?.Any(s => s is null) == true)
+ {
+ loggingContext.LogComment(MessageImportance.Low, "SDKResolverNullMessage", sdkResolver.Name, sdk.ToString());
+ }
  }
  catch (Exception e) when ((e is FileNotFoundException || e is FileLoadException) && sdkResolver.GetType().GetTypeInfo().Name.Equals("NuGetSdkResolver", StringComparison.Ordinal))
  {
@@ -481,7 +488,11 @@ private static void LogWarnings(LoggingContext loggingContext, ElementLocation l
 
  foreach (string warning in warnings)
  {
- loggingContext.LogWarningFromText(null, null, null, new BuildEventFileInfo(location), warning);
+ // Do not fail on returned null messages
+ if (!string.IsNullOrWhiteSpace(warning))
+ {
+ loggingContext.LogWarningFromText(null, null, null, new BuildEventFileInfo(location), warning);
+ }
  }
  }
 

src/Build/Resources/Strings.resx

@@ -1346,6 +1346,12 @@ Errors: {3}</value>
  LOCALIZATION: Do not localize the word SDK. "{2}" is new line separated warnings or "null". "{3}" is new line separated errors or "null".
  </comment>
  </data>
+ <data name="SDKResolverNullMessage" xml:space="preserve">
+ <value>The "{0}" resolver attempted to resolve the SDK "{1}" and returned null as a string in the list of warnings or errors.</value>
+ <comment>
+ LOCALIZATION: Do not localize the word SDK.
+ </comment>
+ </data> 
  <data name="CouldNotRunNuGetSdkResolver" xml:space="preserve">
  <value>The NuGet-based SDK resolver failed to run because NuGet assemblies could not be located. Check your installation of MSBuild or set the environment variable "{0}" to the folder that contains the required NuGet assemblies. {1}</value>
  </data>