Ensure ForwardCancellationTokenAnalyzer treats usages of default expressions properly

src/NServiceBus.Core.Analyzer.Tests.Common/ForwardCancellationToken/ForwardCancellationTokenTests.cs

@@ -479,6 +479,79 @@ public class Bar {}");
     public class ForwardCancellationTokenTestsCSharp8 : ForwardCancellationTokenTests
     {
         protected override LanguageVersion AnalyzerLanguageVersion => LanguageVersion.CSharp8;
+
+        [TestCase("default(CancellationToken)")]
+        [TestCase("default")]
+        [TestCase("CancellationToken.None")]
+        [TestCase("new CancellationToken(true)")]
+        [TestCase("context.CancellationToken")]
+        public Task DefaultTokenParameters(string parameterValue) => Assert(ForwardCancellationTokenAnalyzer.DiagnosticId, @"
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using NServiceBus;
+public class Foo : IHandleMessages<TestMessage>
+{
+    public async Task Handle(TestMessage message, IMessageHandlerContext context)
+    {
+        await Test(""hi"", 1, DateTime.Now, " + parameterValue + @");
+        await Test(default(string), default(int), default(DateTime), " + parameterValue + @");
+        await Test(default, default, default, " + parameterValue + @");
+
+        await [|Test(""hi"", 1, DateTime.Now)|];
+        await [|Test(default(string), default(int), default(DateTime))|];
+        await [|Test(default, default, default)|];
+    }
+
+    Task Test(string s, int i, DateTime d, CancellationToken token = default)
+    {
+        System.Console.WriteLine($""{{s}} {{i}} {{d}}"");
+        return Task.Delay(i, token);
+    }
+}
+public class TestMessage : ICommand {}
+");
+
+#if NET // IAsyncEnumerable requires package Microsoft.Bcl.AsyncInterfaces on .NET Framework
+
+        [TestCase("AsyncEnumerator(context.CancellationToken)")]
+        [TestCase("AsyncEnumerator(CancellationToken.None)")]
+        [TestCase("AsyncEnumerator(default(CancellationToken))")]
+        [TestCase("AsyncEnumerator(default)")]
+        [TestCase("[|AsyncEnumerator()|]")]
+        [TestCase("[|AsyncEnumerator()|].WithCancellation(context.CancellationToken)")]
+        [TestCase("[|AsyncEnumerator()|].WithCancellation(CancellationToken.None)")]
+        [TestCase("[|AsyncEnumerator()|].WithCancellation(default(CancellationToken))")]
+        [TestCase("[|AsyncEnumerator()|].WithCancellation(default)")]
+        public Task AwaitForeach(string asyncCall) => Assert(ForwardCancellationTokenAnalyzer.DiagnosticId, @"
+using System;
+using System.Collections.Generic;
+using System.Runtime.CompilerServices;
+using NServiceBus;
+using System.Threading;
+using System.Threading.Tasks;
+public class Foo : IHandleMessages<TestMessage>
+{
+    public async Task Handle(TestMessage message, IMessageHandlerContext context)
+    {
+        await foreach (int item in " + asyncCall + @")
+        {
+            Console.WriteLine(item);
+        }
+    }
+
+    static async IAsyncEnumerable<int> AsyncEnumerator([EnumeratorCancellation] CancellationToken cancellationToken = default)
+    {
+        for (int i = 0; i < 10; i++)
+        {
+            await Task.Delay(0, cancellationToken);
+            yield return i;
+        }
+    }
+}
+public class TestMessage : ICommand {}
+");
+#endif
     }
 
     public class ForwardCancellationTokenTestsCSharp9 : ForwardCancellationTokenTestsCSharp8

src/NServiceBus.Core.Analyzer.Tests.Common/Helpers/AnalyzerTestFixture.cs

@@ -110,6 +110,8 @@ static AnalyzerTestFixture()
                 MetadataReference.CreateFromFile(typeof(System.Linq.Expressions.Expression).GetTypeInfo().Assembly.Location),
 #if NET
                 MetadataReference.CreateFromFile(Assembly.Load("System.Runtime").Location),
+                MetadataReference.CreateFromFile(Assembly.Load("System.Console").Location),
+                MetadataReference.CreateFromFile(Assembly.Load("System.Private.CoreLib").Location),
 #endif
                 MetadataReference.CreateFromFile(typeof(EndpointConfiguration).GetTypeInfo().Assembly.Location),
                 MetadataReference.CreateFromFile(typeof(IUniformSession).GetTypeInfo().Assembly.Location));

src/NServiceBus.Core.Analyzer/ForwardCancellationTokenAnalyzer.cs

@@ -177,20 +177,46 @@ static bool LooksLikeCancellationToken(ExpressionSyntax expression, string calle
                 }
             }
 
-            if (expression is ObjectCreationExpressionSyntax objectCreation &&
-                objectCreation.Type is IdentifierNameSyntax objectCreationTypeName &&
-                objectCreationTypeName.Identifier.ValueText == "CancellationToken")
+            // new CancellationToken(...)
+            if (expression is ObjectCreationExpressionSyntax objectCreation && TypeSyntaxLooksLikeCancellationToken(objectCreation.Type))
             {
                 return true;
             }
 
+            // default(CancellationToken)
+            if (expression is DefaultExpressionSyntax defaultSyntax && TypeSyntaxLooksLikeCancellationToken(defaultSyntax.Type))
+            {
+                return true;
+            }
+
+            // Note: `default` on its own is a LiteralExpressionSyntax, not a DefaultExpressionSyntax, so when this is used
+            // as a parameter we can't tell whether it's a CancellationToken at the lexical level and must allow IsCancellationToken
+            // to make the determination by consulting the semantic model
             return false;
         }
 
+        static bool TypeSyntaxLooksLikeCancellationToken(TypeSyntax typeSyntax) =>
+            typeSyntax is IdentifierNameSyntax identifierSyntax && identifierSyntax.Identifier.ValueText == "CancellationToken";
+
         static bool IsCancellationToken(ExpressionSyntax expressionSyntax, SyntaxNodeAnalysisContext context, INamedTypeSymbol cancellationTokenType)
         {
-            var expressionSymbol = context.SemanticModel.GetSymbolInfo(expressionSyntax, context.CancellationToken).Symbol;
-            return expressionSymbol.GetTypeSymbolOrDefault()?.Equals(cancellationTokenType, SymbolEqualityComparer.IncludeNullability) ?? false;
+            var typeSymbol = GetTypeSymbolFromExpression(expressionSyntax, context);
+            return typeSymbol?.Equals(cancellationTokenType, SymbolEqualityComparer.IncludeNullability) ?? false;
+        }
+
+        static ITypeSymbol GetTypeSymbolFromExpression(ExpressionSyntax expression, SyntaxNodeAnalysisContext context)
+        {
+            if (expression is LiteralExpressionSyntax) // `default` as a parameter
+            {
+                var typeInfo = context.SemanticModel.GetTypeInfo(expression, context.CancellationToken);
+                return typeInfo.Type;
+            }
+            else
+            {
+                var symbolInfo = context.SemanticModel.GetSymbolInfo(expression, context.CancellationToken);
+                var expressionSymbol = symbolInfo.Symbol;
+                return expressionSymbol.GetTypeSymbolOrDefault();
+            }
         }
 
         static IMethodSymbol GetRecommendedMethod(
@@ -247,7 +273,7 @@ static bool IsCancellationToken(ExpressionSyntax expressionSyntax, SyntaxNodeAna
 
         // if adding a cancellation token to the args will not put it in the right place
         static string GetRequiredArgName(IMethodSymbol recommendedMethod, IParameterSymbol extraParam, SeparatedSyntaxList<ArgumentSyntax> args) =>
-            !recommendedMethod.Parameters[args.Count].Equals(extraParam, SymbolEqualityComparer.IncludeNullability) ? extraParam.Name : null;
+            args.Count < recommendedMethod.Parameters.Length && !recommendedMethod.Parameters[args.Count].Equals(extraParam, SymbolEqualityComparer.IncludeNullability) ? extraParam.Name : null;
 
         static INamedTypeSymbol GetCalledType(InvocationExpressionSyntax call, IMethodSymbol calledMethod, SyntaxNodeAnalysisContext context)
         {