Add support for generic attributes to StronglyTypedIdAttribute

[rfvgyhn]

This PR adds support for generic attributes to StronglyTypedIdAttribute. [StronglyTypedId<int>]

I wasn't sure what the best way to conditionally add a generic version of the attribute. This approach adds an MSBuild file that defines a preprocessor constant to check if the project supports generic attributes.

[meziantou]

Can you rebase your branch? Also, I changed the way attributes are defined. It's now in the Meziantou.Framework.StronglyTypedId.Annotations project. You should be able to use #if NET8_0_OR_GREATER to define the attribute.

[rfvgyhn]

Generic attributes are a csharp 11/.net 7 feature. Do you still want to gate it behind .net8?

[meziantou]

Use the minimum supported version. If it's .net 7, use NET_7_0_OR_GREATER.

[rfvgyhn]

I haven't worked with multi-targeted libs before so correct me if I'm wrong on the following.

Wrapping the attribute definition in NET7_0_OR_GREATER means the reference to the Annotations project in the test project needs to get rid of the TargetFramework=netstandard2.0 property since NET7_0_OR_GREATER would always be false. That then means adding nuget references to the compilation object needs to also account for specific Microsoft.NETCore.App.Ref versions. Does that sound right?

Meziantou.Framework/tests/Meziantou.Framework.StronglyTypedId.Tests/Meziantou.Framework.StronglyTypedId.Tests.csproj

Line 9 in 3f7bd16

<ProjectReference Include="..\..\src\Meziantou.Framework.StronglyTypedId.Annotations\Meziantou.Framework.StronglyTypedId.Annotations.csproj" AdditionalProperties="TargetFramework=netstandard2.0" />

Meziantou.Framework/tests/Meziantou.Framework.StronglyTypedId.Tests/StronglyTypedIdSourceGeneratorTests.cs

Lines 40 to 46 in 3f7bd16

	private static async Task<(GeneratorDriverRunResult GeneratorResult, Compilation OutputCompilation, byte[] Assembly)> GenerateFiles(string sourceText, bool mustCompile = true)
	{
	var compilation = await CreateCompilation(sourceText,
	[
	new NuGetReference("Microsoft.NETCore.App.Ref", "6.0.12", "ref/"),
	new NuGetReference("Newtonsoft.Json", "12.0.3", "lib/netstandard2.0/"),
	]);

+ const string NetCoreVersion =
+ #if NET7_0
+         "7.0.14"
+ #elif NET8_0
+         "8.0.0"
+ #else
+         "6.0.12"
+ #endif
+         ;
var compilation = await CreateCompilation(sourceText,
        [
-            new NuGetReference("Microsoft.NETCore.App.Ref", "6.0.12", "ref/"),
+            new NuGetReference("Microsoft.NETCore.App.Ref", NetCoreVersion, "ref/"),

[meziantou]

Seems ok. I wonder if you can only reference the .NET 8 package in the test or if you need to use #if.

[rfvgyhn]

Only referencing .net8 produces CS1701 errors for most tests.

Expected result.Success to be true because Project cannot build:
error CS1701: Assuming assembly reference 'System.Runtime, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' used by 'Meziantou.Framework.StronglyTypedId.Annotations' matches identity 'System.Runtime, Version=8.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' of 'System.Runtime', you may need to supply runtime policy

I suppose that error could be suppressed via specificDiagnosticOptions. Not sure which you prefer.

I've rebased the branch. Let me know what you think.