Generate a 'readonly record struct' using Roslyn

Question

I can't generate a readonly record struct using Roslyn.

My code:

using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;

var tree = SyntaxFactory.CompilationUnit()
    .AddMembers(
            SyntaxFactory.RecordDeclaration(
                SyntaxFactory.Token(SyntaxKind.RecordKeyword),
                SyntaxFactory.Identifier("A"))
            .WithSemicolonToken(SyntaxFactory.Token(SyntaxKind.SemicolonToken))
            .AddModifiers(
                        SyntaxFactory.Token(SyntaxKind.PublicKeyword),
                        SyntaxFactory.Token(SyntaxKind.ReadOnlyKeyword))
            .WithClassOrStructKeyword(
                SyntaxFactory.Token(SyntaxKind.StructKeyword))
            .WithParameterList(
                SyntaxFactory.ParameterList()))
    .NormalizeWhitespace();

Console.WriteLine(tree.ToFullString());

var refApis = AppDomain.CurrentDomain.GetAssemblies()
    .Where(a => !a.IsDynamic)
    .Select(a => MetadataReference.CreateFromFile(a.Location));

var options = new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary);

var compilation = CSharpCompilation.Create("something", new SyntaxTree[] { tree.SyntaxTree }, refApis, options);
var diag = compilation.GetDiagnostics().Where(e => e.Severity == DiagnosticSeverity.Error).ToList();

foreach (var d in diag)
{
    Console.WriteLine(d);
}

Console.ReadLine();

I get such a result "public readonly record struct A();" and such an error "(1,31): error CS0106: The "readonly" modifier is invalid for this element."

This is strange. I've tried with the same syntax tree and I get the exact same compile error. However, you can also create a syntax tree using CSharpSyntaxTree.ParseText("public readonly record struct A();") and this compiles without the error. Inspecting both syntax trees they look the same but there must be some minor difference not immediately visible that triggers the compile error. — Martin Liversage
– Martin Liversage, Commented Sep 13, 2023 at 12:12

Youssef13 · Accepted Answer · 2023-09-15 08:38:30Z

4

The problem is that the record declaration you're creating has SyntaxKind.RecordDeclaration instead of SyntaxKind.RecordStructDeclaration. Even if you are adding the struct keyword, it doesn't change the SyntaxKind that was originally created. To fix this, you'll need to do it as follows:

            SyntaxFactory.RecordDeclaration(
                SyntaxKind.RecordStructDeclaration,
                SyntaxFactory.Token(SyntaxKind.RecordKeyword),
                SyntaxFactory.Identifier("A"))

instead of

            SyntaxFactory.RecordDeclaration(
                SyntaxFactory.Token(SyntaxKind.RecordKeyword),
                SyntaxFactory.Identifier("A"))

answered Sep 15, 2023 at 8:38

Youssef13

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