How to specify TargetFramework for a newly created Workspace?

Question

I'm about to create tests for my Roslyn code analyzer and to its code fixer. I'm using the generated test project template that contains a lot of predefined methods to apply and verify code fixes.

However, my analyzer's code fixer would replace null to default. Default literal was added only in C# 7.1, but the default project that the generated test helper methods create uses C# 7.0, hence my tests always fail. I don't want to change my analyzer to use default(<type>) (actually there are cases when the type is unknown to the analyzer).

This is how the generated method creates a new workspace with a project:

var solution = new AdhocWorkspace()
    .CurrentSolution
    .AddProject(projectId, TestProjectName, TestProjectName, language)
    .AddMetadataReference(projectId, CorlibReference)
    .AddMetadataReference(projectId, SystemCoreReference)
    .AddMetadataReference(projectId, CSharpSymbolsReference)
    .AddMetadataReference(projectId, CodeAnalysisReference);

I can't figure out how would I able to specify the .NET target framework version there. In a .csproj file, we add this tag:

<TargetFramework>net472</TargetFramework>

How to do the same with Roslyn Code Analyzers?

Answer 1

You need to add custom parse options to choose a different language version. WithProjectParseOptions should do what you want.

var solution = new AdhocWorkspace()
    .CurrentSolution
    .AddProject(projectId, TestProjectName, TestProjectName, language)
    .AddMetadataReference(projectId, CorlibReference)
    .AddMetadataReference(projectId, SystemCoreReference)
    .AddMetadataReference(projectId, CSharpSymbolsReference)
    .AddMetadataReference(projectId, CodeAnalysisReference)
    .WithProjectParseOptions(projectId, new CSharpParseOptions(LanguageVersion.CSharp7_1));