Analyzers for v2

[ltrzesniewski]

I wanted to play a bit with Roslyn, and ZeroLog was a good candidate for some analyzers 🙂

• Implicitly discarding a log message (if you forget to call .Log() for instance) will cause an error:

  

  This works just like if every method that returns a LogMessage (even user-defined ones) were marked with [MustUseReturnValue]. You need to discard the message explicitly if you intend to do so, for instance in helper methods:

  private static void AppendSomething(LogMessage message)
  {
      if (DateTime.Today.DayOfWeek == DayOfWeek.Monday)
          _ = message.Append(" :'( ");
  }

• Passing a string interpolation to ZeroLog in language versions below C# 10 will cause an error a warning:

  

  In older language versions, this would call string.Format and allocate. This screenshot is from VS, I don't know why Rider doesn't display the squiggles, but you'll still get a build error warning.

  Note that in multi-targeted projects, you'll get an older language version by default for targets older than .NET 6.

  I suppose you really don't want to allocate if you use ZeroLog, but maybe this should be a warning instead? 🤔

• You'll get a warning if you reference ZeroLog in a project that uses a language version below C# 10. Maybe that's a bit too harsh, I don't know... That's probably redundant with the previous check.

• The build will fail if you use ZeroLog with an SDK older than .NET 6 (or a Visual Studio older than 2022), since the analyzers wouldn't run.

This will merge into #44, but I opened a separate PR for feedback. Also, feel free to suggest a better wording for the error messages. 🙂

[ltrzesniewski]

Here's why the squiggles don't appear in Rider: https://youtrack.jetbrains.com/issue/RIDER-73394

[ltrzesniewski]

I added a code fix that converts automatically from this:

private static void Test()
{
    _log.Info()
        .Append("Foo ")
        .Append(Guid.NewGuid(), "B")
        .Append(" Bar")
        .Log();
}

to this:

private static void Test()
{
    _log.Info($"Foo {Guid.NewGuid():B} Bar");
}

🙂

It needs a bit more work though.