Add an overload to LogContext.PushProperty to accept a Func<T> delegate.

[mattheys]

I logged an issue #1697 but didn't realise how easy it would be to add the functionaility and do a pull request.

I'm not sure how to best test this, especially to make sure it's thread safe. I've tried the below which both work.

using Serilog;
using Serilog.Context;

Log.Logger = new LoggerConfiguration()
                    .Enrich.FromLogContext()
                    .WriteTo.Console(formatter: new Serilog.Formatting.Compact.CompactJsonFormatter())
                    .CreateLogger();

var stopWatch = System.Diagnostics.Stopwatch.StartNew();
Func<long> GetMillis = () => stopWatch.ElapsedMilliseconds;

using (LogContext.PushProperty("elapsed", GetMillis))
{
    for (int i = 0; i < 10; i++)
    {
        var t = new System.Threading.Thread(() => {
            Log.Information("Thread attempt {i}", i);
            Thread.Sleep(1000);
        });

        t.Start();
        t.Join();
    }

    for (int i = 0; i < 10; i++)
    {
        await Task.Run(async () =>
        {
            Log.Information("Task attempt {i}", i);
            await Task.Delay(1000);
        });
    }

}

Console.ReadKey();

[sungam3r]

Suggested change

/// <returns>A handle to later remove the property from the context.</returns>

[mattheys]

Interesting you flagged this to remove as I took the PropertyEnricher.cs as the template to do this and that line is also in there. However this isn't getting merged anyway but you might want to double check this line to make sure it's right.

serilog/src/Serilog/Core/Enrichers/PropertyEnricher.cs

Line 35 in 81e9dee

/// <returns>A handle to later remove the property from the context.</returns>

[sungam3r]

#1699

[nblumhardt]

Thanks for this @mattheys! As you've discovered, LogContext.Push() enables this use case without needing the additional overload on ILogger etc.

As it's a bit of a niche scenario, and already well-supported without additional code in the core, I think we should leave things as-is.