Add support for detecting experimental features in tests, benchmarks,…

… examples, and docs.

build/Common.nonprod.props

@@ -44,4 +44,24 @@
 
     <Message Importance="high" Text="Skipping test execution for '$(TargetPath)' because it does not contain the '$(TargetFramework)' target." Condition="'$(_SkipTests)' == 'true'" />
   </Target>
+
+  <Target Name="ResolveExposedExperimentalFeatures" BeforeTargets="CoreCompile">
+    <!-- Note: What this does is look for $(ProjectReferenceName).BuildFlags.txt
+        files for all the dependencies of the project being compiled. If
+        ExposeExperimentalFeatures=true is found in those files we set compiler
+        constants for each project where experimental features were exposed.
+        Example:
+        OPENTELEMETRY_EXPORTER_INMEMORY_EXPERIMENTAL_FEATURES_EXPOSED;OPENTELEMETRY_EXPERIMENTAL_FEATURES_EXPOSED;OPENTELEMETRY_API_EXPERIMENTAL_FEATURES_EXPOSED;OPENTELEMETRY_API_PROVIDERBUILDEREXTENSIONS_EXPERIMENTAL_FEATURES_EXPOSED
+        -->
+    <ItemGroup>
+      <DependenciesWithExposedExperimentalFeatures
+        Include="@(_ResolvedProjectReferencePaths->'%(Filename)')"
+        Condition="$([System.IO.File]::Exists('%(RootDir)%(Directory)%(Filename).BuildFlags.txt')) AND $([System.IO.File]::ReadAllText('%(RootDir)%(Directory)%(Filename).BuildFlags.txt').Contains('ExposeExperimentalFeatures=true'))" />
+      <CompilerConstantsForDependenciesWithExposedExperimentalFeatures Include="@(DependenciesWithExposedExperimentalFeatures->'$([System.String]::Copy('%(DependenciesWithExposedExperimentalFeatures.Identity)').ToUpper().Replace('.', '_'))_EXPERIMENTAL_FEATURES_EXPOSED')" />
+    </ItemGroup>
+
+    <PropertyGroup Condition="'@(CompilerConstantsForDependenciesWithExposedExperimentalFeatures)' != ''">
+      <DefineConstants>$(DefineConstants);@(CompilerConstantsForDependenciesWithExposedExperimentalFeatures)</DefineConstants>
+    </PropertyGroup>
+  </Target>
 </Project>

build/Common.prod.props

@@ -39,6 +39,10 @@
   <ItemGroup>
     <None Include="$(MSBuildThisFileDirectory)opentelemetry-icon-color.png" Pack="true" PackagePath="\" />
     <SourceRoot Condition="'$(Deterministic)'=='true'" Include="$(MSBuildThisFileDirectory)/" />
+    <None Include="$(IntermediateOutputPath)$(ProjectName).BuildFlags.txt"
+          Link="$(ProjectName).BuildFlags.txt"
+          CopyToOutputDirectory="PreserveNewest"
+          Visible="false" />
     <!-- Note: This includes all the PublicApiAnalyzers files in projects to make editing easier in the IDE -->
     <None Include=".publicApi\**\PublicAPI.*.txt" />
   </ItemGroup>
@@ -82,6 +86,15 @@
       <DefineConstants>$(DefineConstants);EXPOSE_EXPERIMENTAL_FEATURES</DefineConstants>
     </PropertyGroup>
 
+    <!-- Note: We write a file into the output dir which captures the state of
+    ExposeExperimentalFeatures for the current compilation. This is used by
+    consuming projects (tests, benchmarks, examples, etc) to add compiler
+    constants which can be used to detect experimental APIs -->
+    <WriteLinesToFile
+      File="$(OutputPath)$(ProjectName).BuildFlags.txt"
+      Lines="ExposeExperimentalFeatures=$(ExposeExperimentalFeatures)"
+      Overwrite="true"/>
+
     <!-- Note: This selects the correct PublicApiAnalyzers files based on $(ExposeExperimentalFeatures) -->
     <ItemGroup>
       <AdditionalFiles Include=".publicApi\Stable\PublicAPI.*.txt" />

test/OpenTelemetry.Api.Tests/Logs/LoggerProviderTests.cs

@@ -62,7 +62,11 @@ private sealed class NoopLoggerProvider : LoggerProvider
 
     private sealed class TestLoggerProvider : LoggerProvider
     {
+#if OPENTELEMETRY_API_EXPERIMENTAL_FEATURES_EXPOSED
         protected override bool TryCreateLogger(
+#else
+        internal override bool TryCreateLogger(
+#endif
             string? name,
 #if NETSTANDARD2_1_OR_GREATER || NET6_0_OR_GREATER
             [NotNullWhen(true)]