C# 14 Interceptors - The HttpClient Interceptor Generator

HttpClientInterceptorGenerator.cs

using System.Collections.Immutable;
using System.Text;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.CSharp.Syntax;

namespace CorrelationInterceptors.Generator;

[Generator]
public sealed class HttpClientInterceptorGenerator : IIncrementalGenerator
{
    public void Initialize(IncrementalGeneratorInitializationContext context)
    {
        var targets = context.SyntaxProvider
            .CreateSyntaxProvider(
                predicate: static (node, _) => IsSendAsyncInvocation(node),
                transform: static (ctx, ct)  => GetTargetOrNull(ctx, ct))
            .Where(static t => t is not null)
            .Select(static (t, _) => t!)
            .Collect();

        // Generate implementation: https://gist.github.com/AnthonyGiretti/e9413cce4b72452c4006e90b97427fcd
        context.RegisterSourceOutput(targets, Generate);
    }

    private static bool IsSendAsyncInvocation(SyntaxNode node)
        => node is InvocationExpressionSyntax
        {
            Expression: MemberAccessExpressionSyntax { Name.Identifier.Text: "SendAsync" }
        };

    private static InterceptorTarget? GetTargetOrNull(
        GeneratorSyntaxContext ctx,
        System.Threading.CancellationToken ct)
    {
        var invocation = (InvocationExpressionSyntax)ctx.Node;

        // Skip generated files, prevents the generator from intercepting
        // the SendAsync calls it already emitted in HttpClientInterceptors.g.cs
        var filePath = invocation.SyntaxTree.FilePath;
        if (filePath.EndsWith(".g.cs", System.StringComparison.OrdinalIgnoreCase)
            || filePath.EndsWith(".generated.cs", System.StringComparison.OrdinalIgnoreCase))
            return null;

        if (ctx.SemanticModel.GetSymbolInfo(invocation, ct).Symbol
                is not IMethodSymbol method)
            return null;

        if (method.ContainingType.ToDisplayString() != "System.Net.Http.HttpClient"
            || method.Name != "SendAsync")
            return null;

        // GetInterceptableLocation is an extension method on SemanticModel
        // from Microsoft.CodeAnalysis.CSharp, no cast to CSharpSemanticModel needed
        var location = ctx.SemanticModel.GetInterceptableLocation(invocation, ct);
        if (location is null) return null;

        var secondParamType = method.Parameters.Length >= 2
            ? method.Parameters[1].Type.ToDisplayString()
            : string.Empty;

        return new InterceptorTarget(location, method.Parameters.Length, secondParamType);
    }
}

internal sealed class InterceptorTarget
{
    public InterceptableLocation Location        { get; }
    public int                   ParameterCount  { get; }
    public string                SecondParamType { get; }

    public InterceptorTarget(
        InterceptableLocation location, int parameterCount, string secondParamType)
    {
        Location        = location;
        ParameterCount  = parameterCount;
        SecondParamType = secondParamType;
    }
}