Automatically generate .NETStandard compat errors (#57057)

* Automatically generate .NETStandard compat errors

Before this change, a project had to explicitly add a
NETStandardCompatError item to declare that a given tfm range
shouldn't be supported when packaging.

Automate this logic so that projects don't need to specify the item
themselves anymore. Instead condition the NETStandardCompatError target
calcuation logic on the existence of both a .NETStandard and a
.NETCoreApp tfm.

* Update Directory.Build.targets

* Update packaging.targets

* Update eng/packaging.targets

Co-authored-by: Santiago Fernandez Madero <safern@microsoft.com>

Co-authored-by: Santiago Fernandez Madero <safern@microsoft.com>

1 files changed, 45 insertions, 1 deletions

diff --git a/eng/packaging.targets b/eng/packaging.targets
index 30d7ef75d98..4da97847376 100644
--- a/eng/packaging.targets
+++ b/eng/packaging.targets
@@ -12,7 +12,7 @@
     <!-- Don't include target platform specific dependencies, since we use the target platform to represent RIDs instead -->
     <SuppressDependenciesWhenPacking Condition="'$(ExcludeFromPackage)' == 'true' or ('$(TargetsAnyOS)' != 'true' and $([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)', 'net5.0')))">true</SuppressDependenciesWhenPacking>
     <PackageDesignerMarkerFile>$(MSBuildThisFileDirectory)useSharedDesignerContext.txt</PackageDesignerMarkerFile>
-    <GenerateNuspecDependsOn>IncludeAnalyzersInPackage;$(GenerateNuspecDependsOn)</GenerateNuspecDependsOn>
+    <BeforePack>AddNETStandardCompatErrorFileForPackaging;IncludeAnalyzersInPackage;$(BeforePack)</BeforePack>
     <!-- Generate packages in the allconfigurations build. -->
     <GeneratePackageOnBuild Condition="'$(BuildAllConfigurations)' == 'true'">true</GeneratePackageOnBuild>
     <!-- Search for the documentation file in the intellisense package and otherwise pick up the generated one. -->
@@ -127,4 +127,48 @@
     </ItemGroup>
   </Target>
 
+  <!-- Include a netstandard compat error if the project targets both .NETStandard and
+       .NETCoreApp. This prohibits users to consume packages on an older .NETCoreApp version
+       than the minimum supported one. -->
+  <ItemGroup Condition="'$(DisableNETStandardCompatErrorForNETCoreApp)' != 'true'">
+    <NETStandardCompatError Include="netcoreapp2.0"
+                            Supported="$(NetCoreAppMinimum)"
+                            Condition="$(TargetFrameworks.Contains('netstandard2.')) and
+                                       ($(TargetFrameworks.Contains('$(NetCoreAppMinimum)')) or $(TargetFrameworks.Contains('$(NetCoreAppCurrent)')))" />
+  </ItemGroup>
+
+  <!-- Add targets file that marks a .NETStandard applicable tfm as unsupported. -->
+  <Target Name="AddNETStandardCompatErrorFileForPackaging"
+          Condition="'@(NETStandardCompatError)' != ''"
+          Inputs="%(NETStandardCompatError.Identity)"
+          Outputs="unused">
+    <PropertyGroup>
+      <_NETStandardCompatErrorFilePath>$(BaseIntermediateOutputPath)netstandardcompaterrors\%(NETStandardCompatError.Identity)\$(PackageId).targets</_NETStandardCompatErrorFilePath>
+      <_NETStandardCompatErrorFileTarget>NETStandardCompatError_$(PackageId.Replace('.', '_'))_$([System.String]::new('%(NETStandardCompatError.Supported)').Replace('.', '_'))</_NETStandardCompatErrorFileTarget>
+      <_NETStandardCompatErrorFileContent>
+<![CDATA[<Project InitialTargets="$(_NETStandardCompatErrorFileTarget)">
+  <Target Name="$(_NETStandardCompatErrorFileTarget)"
+          Condition="'%24(SuppressTfmSupportBuildWarnings)' == ''">
+    <Error Text="$(PackageId) doesn't support %24(TargetFramework). Consider updating your TargetFramework to %(NETStandardCompatError.Supported) or later." />
+  </Target>
+</Project>]]>
+      </_NETStandardCompatErrorFileContent>
+    </PropertyGroup>
+
+    <WriteLinesToFile File="$(_NETStandardCompatErrorFilePath)"
+                      Lines="$(_NETStandardCompatErrorFileContent)"
+                      Overwrite="true"
+                      WriteOnlyWhenDifferent="true" />
+
+    <ItemGroup>
+      <None Include="$(_NETStandardCompatErrorFilePath)"
+            PackagePath="buildTransitive\%(NETStandardCompatError.Identity)"
+            Pack="true" />
+      <None Include="$(PlaceholderFile)"
+            PackagePath="buildTransitive\%(NETStandardCompatError.Supported)"
+            Pack="true" />
+      <FileWrites Include="$(_NETStandardCompatErrorFilePath)" />
+    </ItemGroup>
+  </Target>
+
 </Project>