Fix vmr build number (#19217)

eng/pipelines/templates/jobs/vmr-build.yml

@@ -321,6 +321,8 @@ jobs:
           # Allows Arcade to have access to the commit for the build, pass it through to the container
           customEnvVars="$customEnvVars BUILD_SOURCEVERSION=$BUILD_SOURCEVERSION"
 
+          customEnvVars="$customEnvVars BUILD_BUILDNUMBER=$(Build.BuildNumber)"
+
           customDockerRunArgs=""
           for envVar in $customEnvVars; do
             customDockerRunArgs="$customDockerRunArgs -e $envVar"

src/SourceBuild/content/Directory.Build.props

@@ -214,12 +214,6 @@
     <PoisonedReportFile>$(PackageReportDir)poisoned.txt</PoisonedReportFile>
   </PropertyGroup>
 
-  <!-- The predefined environmental variable `BUILD_BUILDNUMBER` is getting overwritten in repo-projects,
-    so save it in a different varialbe-->
-  <PropertyGroup>
-    <VmrBuildNumber>$(BUILD_BUILDNUMBER)"</VmrBuildNumber>
-  </PropertyGroup>
-
   <Import Project="$(GitInfoAllRepoPropsFile)" />
 
 </Project>

src/SourceBuild/content/build.proj

@@ -36,10 +36,11 @@
       <RepoAssetManifest Include="$(AssetManifestsIntermediateDir)\**\*.xml" />
     </ItemGroup>
 
+    <!-- It's OK for the VmrBuildNumber to be empty -->
     <Microsoft.DotNet.UnifiedBuild.Tasks.MergeAssetManifests 
       AssetManifest="@(RepoAssetManifest)" 
       MergedAssetManifestOutputPath="$(MergedAssetManifestOutputPath)"
-      VmrBuildNumber="$(VmrBuildNumber)" />
+      VmrBuildNumber="$(BUILD_BUILDNUMBER)" />
   </Target>
 
   <Import Project="$(RepositoryEngineeringDir)build.sourcebuild.targets" Condition="'$(DotNetBuildSourceOnly)' == 'true'" />

src/SourceBuild/content/eng/tools/tasks/Microsoft.DotNet.UnifiedBuild.Tasks/MergeAssetManifests.cs

@@ -31,8 +31,7 @@ namespace Microsoft.DotNet.UnifiedBuild.Tasks
         /// <summary>
         /// Azure DevOps build number
         /// </summary>
-        [Required]
-        public required string VmrBuildNumber { get; init; }
+        public string VmrBuildNumber { get; set; } = string.Empty;
 
         private static readonly string _buildIdAttribute = "BuildId";
         private static readonly string _azureDevOpsBuildNumberAttribute = "AzureDevOpsBuildNumber";