Do not generate reports with no coverage (Azure#17293)

Fixes Azure#17286

Author: heaths

eng/CodeCoverage.targets

@@ -24,16 +24,34 @@
   </ItemGroup>
 
   <!-- Clean up previous TestResults so reports are recent. -->
-  <Target Name="CleanPreviousCodeCoverage"
+  <Target Name="_CleanPreviousCodeCoverage"
           BeforeTargets="VSTest"
           Condition="'$(_CollectCoverage)' == 'true'">
     <RemoveDir Directories="$(_TestResultsDirectory)" />
   </Target>
 
+  <!-- Set a variable to indicate that a report can be generated. -->
+  <Target Name="_SetCoverageCollected"
+          AfterTargets="VSTest"
+          Condition="'$(_CollectCoverage)' == 'true'">
+    <ItemGroup>
+      <_CoverageFiles Include="$(_TestResultsDirectory)\**\coverage.cobertura.xml" />
+    </ItemGroup>
+    <PropertyGroup>
+      <_CoverageCollected Condition="'@(_CoverageFiles)' != ''">true</_CoverageCollected>
+    </PropertyGroup>
+
+    <!-- Indicate to the pipeline a report can be generated. -->
+    <Message Importance="high"
+             Condition="'$(_CoverageCollected)' == 'true' and '$(TF_BUILD)' == 'true'"
+             Text="##vso[task.setvariable variable=coverage.collected]true" />
+  </Target>
+
   <!-- Should be similar to what's in the pipelines, though generate a full HTML report. -->
   <Target Name="GenerateCodeCoverageReport"
           AfterTargets="VSTest"
-          Condition="'$(_CollectCoverage)' == 'true' and '$(SkipCoverageReport)' != 'true'">
+          DependsOnTargets="_SetCoverageCollected"
+          Condition="'$(_CollectCoverage)' == 'true' and '$(SkipCoverageReport)' != 'true' and '$(_CoverageCollected)' == 'true'">
     <PropertyGroup>
       <CoverageReportCommandLine>dotnet tool run reportgenerator --</CoverageReportCommandLine>
       <CoverageReportCommandLine>$(CoverageReportCommandLine) "-reports:$(_TestResultsDirectory)\**\coverage.cobertura.xml"</CoverageReportCommandLine>

eng/pipelines/templates/jobs/archetype-sdk-client.yml

@@ -110,8 +110,6 @@ jobs:
     condition: and(succeededOrFailed(), ne(variables['Skip.Test'], true))
     variables:
       - template: ../variables/globals.yml
-      - name: disable.coverage.autogenerate
-        value: true
     strategy:
       maxParallel: $[ variables['MaxParallelTestJobs'] ]
       matrix:
@@ -167,18 +165,17 @@ jobs:
           testResultsFormat: "VSTest"
           mergeTestResults: true
       - task: Palmmedia.reportgenerator.reportgenerator-build-release-task.reportgenerator@4
-        condition: and(succeededOrFailed(), eq(variables['CollectCoverage'], 'true'))
+        condition: and(succeededOrFailed(), eq(variables['CollectCoverage'], 'true'), eq(variables['coverage.collected'], 'true'))
         displayName: Generate Code Coverage Reports
         inputs:
           reports: $(Build.SourcesDirectory)\sdk\${{parameters.ServiceDirectory}}\**\coverage.cobertura.xml
           targetdir: $(Build.ArtifactStagingDirectory)\coverage
-          reporttypes: Cobertura;HtmlInline_AzurePipelines
+          reporttypes: Cobertura
           filefilters: +$(Build.SourcesDirectory)\sdk\${{parameters.ServiceDirectory}}\**
           verbosity: Verbose
       - task: PublishCodeCoverageResults@1
-        condition: and(succeededOrFailed(), eq(variables['CollectCoverage'], 'true'))
+        condition: and(succeededOrFailed(), eq(variables['CollectCoverage'], 'true'), eq(variables['coverage.collected'], 'true'))
         displayName: Publish Code Coverage Reports
         inputs:
           codeCoverageTool: Cobertura
           summaryFileLocation: $(Build.ArtifactStagingDirectory)\coverage\Cobertura.xml
-          reportDirectory: $(Build.ArtifactStagingDirectory)\coverage