[Bug]: Breaks with multiple framework targets

[ds5678]

On a brand new project with this csproj file, everything compiles fine:

<Project Sdk="Microsoft.NET.Sdk">

	<PropertyGroup>
		<TargetFramework>netstandard2.0</TargetFramework>
	</PropertyGroup>

	<ItemGroup>
		<PackageReference Include="TunnelVisionLabs.ReferenceAssemblyAnnotator" Version="1.0.0-alpha.160" PrivateAssets="all" />

		<!-- Specifies the version of Microsoft.NETCore.App.Ref to obtain nullability information from. -->
		<PackageDownload Include="Microsoft.NETCore.App.Ref" Version="[6.0.0]" />
	</ItemGroup>

</Project>

However, if the csproj file is changed slightly, it no longer does:

<Project Sdk="Microsoft.NET.Sdk">

	<PropertyGroup>
		<TargetFrameworks>netstandard2.0</TargetFrameworks>
	</PropertyGroup>

	<ItemGroup>
		<PackageReference Include="TunnelVisionLabs.ReferenceAssemblyAnnotator" Version="1.0.0-alpha.160" PrivateAssets="all" />

		<!-- Specifies the version of Microsoft.NETCore.App.Ref to obtain nullability information from. -->
		<PackageDownload Include="Microsoft.NETCore.App.Ref" Version="[6.0.0]" />
	</ItemGroup>

</Project>

In Visual Studio 2022, I get this error:

MSB4184	The expression """.Substring(1)" cannot be evaluated. startIndex cannot be larger than length of string. Parameter name: startIndex

This points to a line in TunnelVisionLabs.ReferenceAssemblyAnnotator.targets:

<PropertyGroup Condition="'$(TargetFrameworkVersion.Substring(1))' &gt;= '2.0'">

[R2D221]

Not sure how useful it will be here, but I never had this problem because I added the dependency only for the frameworks who need it.

Like so:

<ItemGroup Condition="'$(TargetFramework)' == 'net461'">
  <PackageReference Include="TunnelVisionLabs.ReferenceAssemblyAnnotator" Version="1.0.0-alpha.160">
    <PrivateAssets>all</PrivateAssets>
    <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
  </PackageReference>
  <PackageDownload Include="Microsoft.NETCore.App.Ref" Version="[7.0.0]" />
</ItemGroup>

[ds5678]

@R2D221 thank you for the recommendation. Unfortunately, I have moved on from this repository. I have used the following alternatives in other projects:

• Nullable is a polyfill for nullable attributes.
• PolySharp is a polyfill for many classes, including nullable attributes.