Don't try to apply xUnit2023 fixer for non-standalone expressions

Author: bradwilson

src/xunit.analyzers.fixes/X2000/AssertSingleShouldBeUsedForSingleParameterFixer.cs

@@ -99,9 +99,18 @@ public override async Task RegisterCodeFixesAsync(CodeFixContext context)
 		if (!diagnostic.Properties.TryGetValue(Constants.Properties.Replacement, out var replacement) || replacement is null)
 			return;
 
+		// We want to remove the 'await' in front of 'Assert.CollectionAsync' since 'Assert.Single' doesn't need it
+		var nodeToReplace = invocation.Parent;
+		if (assertMethodName == Constants.Asserts.CollectionAsync && nodeToReplace is AwaitExpressionSyntax)
+			nodeToReplace = nodeToReplace.Parent;
+
+		// Can't replace something that's not a standlone expression
+		if (nodeToReplace is not ExpressionStatementSyntax)
+			return;
+
 		context.RegisterCodeFix(
 			XunitCodeAction.Create(
-				ct => UseSingleMethod(context.Document, invocation, assertMethodName, replacement, ct),
+				ct => UseSingleMethod(context.Document, invocation, nodeToReplace, assertMethodName, replacement, ct),
 				Key_UseSingleMethod,
 				"Use Assert.{0}", replacement
 			),
@@ -112,6 +121,7 @@ public override async Task RegisterCodeFixesAsync(CodeFixContext context)
 	static async Task<Document> UseSingleMethod(
 		Document document,
 		InvocationExpressionSyntax invocation,
+		SyntaxNode nodeToReplace,
 		string assertMethodName,
 		string replacementMethod,
 		CancellationToken cancellationToken)
@@ -131,10 +141,6 @@ static async Task<Document> UseSingleMethod(
 						.WithArgumentList(ArgumentList(SeparatedList([Argument(invocation.ArgumentList.Arguments[0].Expression)])))
 						.WithExpression(memberAccess.WithName(IdentifierName(replacementMethod)));
 
-				// We want to replace the whole expression, because it may include an unnecessary await, as we may be
-				// converting from Assert.CollectionAsync (which needs await) to Assert.Single (which does not).
-				var nodeToReplace = invocation.FirstAncestorOrSelf<ExpressionStatementSyntax>() ?? invocation.Parent;
-
 				if (invocation.ArgumentList.Arguments[1].Expression is SimpleLambdaExpressionSyntax lambdaExpression)
 				{
 					var originalParameterName = lambdaExpression.Parameter.Identifier.Text;

src/xunit.analyzers.tests/Fixes/X2000/AssertSingleShouldBeUsedForSingleParameterFixerTests.cs

@@ -6,6 +6,28 @@
 
 public class AssertSingleShouldBeUsedForSingleParameterFixerTests
 {
+	[Fact]
+	public async ValueTask CannotFixInsideLambda()
+	{
+		var source = /* lang=c#-test */ """
+			using System.Collections.Generic;
+			using System.Threading.Tasks;
+			using Xunit;
+			
+			public class TestClass {
+				[Fact]
+				public static void TestMethod()
+				{
+					Record.Exception(
+						() => [|Assert.Collection(default(IEnumerable<object>), item => Assert.True(false))|]
+					);
+				}
+			}
+			""";
+
+		await Verify.VerifyCodeFix(LanguageVersion.CSharp8, source, source, AssertSingleShouldBeUsedForSingleParameterFixer.Key_UseSingleMethod);
+	}
+
 	[Fact]
 	public async ValueTask EnumerableAcceptanceTest()
 	{