Enable attribute preservation by default, to enable the usage analyzers

Author: andrewlock

README.md

@@ -624,7 +624,7 @@ If you wish to preserve these attributes in the build output, you can define the
   </PropertyGroup>
 
   <!-- Add the package -->
-  <PackageReference Include="NetEscapades.EnumGenerators" Version="1.0.0-beta20" PrivateAssets="all" />
+  <PackageReference Include="NetEscapades.EnumGenerators" Version="1.0.0-beta20" />
   <!--              ☝ You must not exclude the runtime assets in this case -->
 
 </Project>

src/NetEscapades.EnumGenerators/NetEscapades.EnumGenerators.csproj

@@ -21,5 +21,6 @@
 
   <ItemGroup>
     <None Include="README.md" Pack="true" PackagePath="\" />
+    <None Include="NetEscapades.EnumGenerators.targets" Pack="true" PackagePath="buildTransitive" Visible="true" />
   </ItemGroup>
 </Project>

src/NetEscapades.EnumGenerators/NetEscapades.EnumGenerators.targets

@@ -0,0 +1,21 @@
+<Project>
+  <!--
+    Define NETESCAPADES_ENUMGENERATORS_USAGES so that the [Conditional] attribute on [EnumExtensions]
+    is satisfied. This preserves the attribute in IL, enabling usage analyzers to detect decorated
+    enums in referenced assemblies.
+
+    This targets file is only included in the meta-package, so it only runs when the meta-package is
+    referenced. We additionally verify the Attributes assembly will be available at runtime by checking
+    ReferenceCopyLocalPaths, which guards against unsupported configurations like ExcludeAssets="runtime".
+
+    Set EnumGenerator_PreserveAttributes to "false" to disable this behavior.
+
+    Note: using PrivateAssets="All" or ExcludeAssets="runtime" on the meta-package is not supported.
+  -->
+  <Target Name="NetEscapadesEnumGenerators_DefineUsages" AfterTargets="ResolveReferences" BeforeTargets="CoreCompile"
+          Condition="'$(EnumGenerator_PreserveAttributes)' != 'false'">
+    <PropertyGroup>
+      <DefineConstants Condition="'@(ReferenceCopyLocalPaths->AnyHaveMetadataValue(`FileName`, `NetEscapades.EnumGenerators.Attributes`))' == 'True'">$(DefineConstants);NETESCAPADES_ENUMGENERATORS_USAGES</DefineConstants>
+    </PropertyGroup>
+  </Target>
+</Project>

tests/NetEscapades.EnumGenerators.NetStandard.Interceptors.IntegrationTests/NetEscapades.EnumGenerators.NetStandard.Interceptors.IntegrationTests.csproj

@@ -30,6 +30,8 @@
                       OutputItemType="Analyzer" ReferenceOutputAssembly="true" />
   </ItemGroup>
 
+  <Import Project="..\..\src\NetEscapades.EnumGenerators\NetEscapades.EnumGenerators.targets" />
+
   <ItemGroup>
     <Content Include="..\NetEscapades.EnumGenerators.IntegrationTests\xunit.runner.json" CopyToOutputDirectory="PreserveNewest" />
   </ItemGroup>