Syntax node actions for partial constructors are not called for the defining part #86086

using System.Collections.Concurrent;
using System.Collections.Immutable;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.Diagnostics;

namespace PartialConstructorTestProject;

[TestClass]
public sealed class PartialConstructorTests
{
    [TestMethod]
    public async Task SyntaxNodeAction_IsCalledForBothPartsOfPartialConstructor()
    {
        var source = """
            public partial class C
            {
                public partial C(int x);
                public partial C(int x) { }
            }
            """;
        var compilation = CSharpCompilation.Create(
            "Test",
            [CSharpSyntaxTree.ParseText(source, new CSharpParseOptions(LanguageVersion.Default))],
            [MetadataReference.CreateFromFile(typeof(object).Assembly.Location)],
            new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary));
        Assert.IsEmpty(compilation.GetDiagnostics());

        var analyzer = new ConstructorRecordingAnalyzer();
        await compilation.WithAnalyzers([analyzer]).GetAnalyzerDiagnosticsAsync();
        Assert.AreEqual("3, 4", string.Join(", ", analyzer.VisitedLines.Order())); // Fails here with only 4
    }

    [DiagnosticAnalyzer(LanguageNames.CSharp)]
    private sealed class ConstructorRecordingAnalyzer : DiagnosticAnalyzer
    {
        private static readonly DiagnosticDescriptor Descriptor = new(
            "TEST0001", "Unused", "Unused", "Test", DiagnosticSeverity.Warning, isEnabledByDefault: true);

        public ConcurrentBag<int> VisitedLines { get; } = [];

        public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => [Descriptor];

        public override void Initialize(AnalysisContext context)
        {
            context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
            context.EnableConcurrentExecution();
            context.RegisterSyntaxNodeAction(HandleConstructor, SyntaxKind.ConstructorDeclaration);
        }

        private void HandleConstructor(SyntaxNodeAnalysisContext c)
        {
            VisitedLines.Add(c.Node.GetLocation().GetLineSpan().StartLinePosition.Line + 1);
        }
    }
}