CA1068: Allow caller attributes to come after cancellation token

[Youssef1313]

Fixes #4227

[Evangelink]

@Youssef1313 Have you been able to reproduce the issue? I couldn't...

[Youssef1313]

@Evangelink I haven't tried, this PR was just a quick edit from GitHub UI 😄
But it's strange if the problem doesn't reproduce, I can't see anywhere in the existing code that it treats these attributes in any special way.

[Youssef1313]

@Evangelink I read through the code again and I think I got it. The cancellation token should be optional to reproduce.
I'll open a draft PR to check test results from CI (opened #4229).

[Evangelink]

@Youssef1313 I don't think so, some tests are raising an issue without having the parameter with a default value:

[Fact]
        public async Task DiagnosticOnExtensionMethodWhenCancellationTokenIsNotFirstParameter()
        {
            var test = @"
using System.Threading;
static class C1
{
    public static void M1(this object p1, CancellationToken p2, object p3)
    {
    }
}";

            var expected = VerifyCS.Diagnostic().WithLocation(5, 24).WithArguments("C1.M1(object, System.Threading.CancellationToken, object)");
            await VerifyCS.VerifyAnalyzerAsync(test, expected);
        }

[Youssef1313]

@Evangelink If optional parameter exists, the analyzer behavior is different based on whether the cancellation token is optional or not.

• If cancellation token is optional: report diagnostic.
• If cancellation token isn't optional: don't report because it cannot come last in this case.

So:

    public Task SomeAsync(CancellationToken cancellationToken,
        [CallerMemberName] string memberName = """",
        [CallerFilePath] string sourceFilePath = """",
        [CallerLineNumber] int sourceLineNumber = 0)
    {
        throw new NotImplementedException();
    } 

The above currently doesn't report diagnostic, which is correct.

---

    public Task SomeAsync(CancellationToken cancellationToken = default,
        [CallerMemberName] string memberName = """",
        [CallerFilePath] string sourceFilePath = """",
        [CallerLineNumber] int sourceLineNumber = 0)
    {
        throw new NotImplementedException();
    } 

But the above code will report diagnostic, this is the case reported in #4227

---

I haven't confirmed this, but both tests are added in this draft #4229, so waiting for CI to confirm.

---

Edit: @Evangelink The CI build in #4229 has completed and confirms that this analyzer reports a diagnostic when cancellation token is optional and is followed by caller information parameters. I'll close the draft PR once you give the build results a look.

[Youssef1313]

@mavasani This is preferred to be squashed when merging.

[codecov]

Codecov Report

Merging #4228 into master will increase coverage by 0.00%.
The diff coverage is 98.88%.

@@           Coverage Diff            @@
##           master    #4228    +/-   ##
========================================
  Coverage   95.80%   95.80%            
========================================
  Files        1170     1170            
  Lines      264435   264599   +164     
  Branches    15959    15966     +7     
========================================
+ Hits       253333   253504   +171     
+ Misses       9087     9081     -6     
+ Partials     2015     2014     -1     

[Evangelink]

LGTM

[mavasani]

Change looks good, but needs moving well known type computation logic into CompilationStartAction.