Respect ExcludeSolutions when calculating the build graph

build/repo.targets

@@ -110,13 +110,19 @@
      DependsOnTargets="_PrepareRepositories;_CreateRepositoriesListWithCommits;_UpdateNuGetConfig;_GenerateBuildGraph;_BuildRepositories" />
 
   <Target Name="_PrepareRestoreGraphSpecs" DependsOnTargets="_PrepareRepositories">
-    <ItemGroup>
-      <Solution Include="$(_CloneRepositoryRoot)%(Repository.Identity)\*.sln">
-        <Repository>%(Repository.Identity)</Repository>
-      </Solution>
 
+    <MSBuild Projects="$(MSBuildProjectFullPath)"
+             Targets="ResolveSolutions"
+             Properties="RepositoryRoot=$(_CloneRepositoryRoot)%(Repository.Identity)\"
+             ContinueOnError="WarnAndContinue">
+      <Output TaskParameter="TargetOutputs" ItemName="Solution" />
+    </MSBuild>
+
+    <Error Text="No solutions were found in '$(_CloneRepositoryRoot)'" Condition="@(Solution->Count()) == 0" />
+
+    <ItemGroup>
       <Solution>
-        <AdditionalProperties>RestoreGraphOutputPath=$(_RestoreGraphSpecsDirectory)%(Solution.Repository)\%(Solution.FileName)%(Solution.Extension).json</AdditionalProperties>
+        <AdditionalProperties>RestoreGraphOutputPath=$(_RestoreGraphSpecsDirectory)$([System.IO.Path]::GetFileName('$([System.IO.Path]::GetDirectoryName(%(FullPath)))'))\%(Solution.FileName)%(Solution.Extension).json</AdditionalProperties>
       </Solution>
 
       <GraphSpecInputs Include="

build/tasks/BuildGraph/DependencyGraphSpecProvider.cs

@@ -15,6 +15,12 @@ namespace RepoTools.BuildGraph
         public DependencyGraphSpec GetDependencyGraphSpec(string repositoryName, string solutionPath)
         {
             var outputFile = Path.Combine(_packageSpecDirectory, repositoryName, Path.GetFileName(solutionPath) + ".json");
+
+            if (!File.Exists(outputFile))
+            {
+                return null;
+            }
+
             return DependencyGraphSpec.Load(outputFile);
         }
     }

build/tasks/BuildGraph/Repository.cs

@@ -56,6 +56,11 @@ namespace RepoTools.BuildGraph
             foreach (var file in solutionFiles)
             {
                 var spec = provider.GetDependencyGraphSpec(name, file);
+                if (spec == null)
+                {
+                    continue;
+                }
+
                 var projects = spec.Projects.OrderBy(p => p.RestoreMetadata.ProjectStyle == ProjectStyle.PackageReference ? 0 : 1);
                 foreach (var specProject in projects)
                 {