Fix UNT0006 when a Unity message is wrongly referenced.

src/Microsoft.Unity.Analyzers.Tests/MessageSignatureTests.cs

@@ -116,7 +116,7 @@ bool OnPreGeneratingCSProjectFiles(int foo)
 	[Fact]
 	public async Task MessageSignatureUnityLogic()
 	{
-		// Unity allows to specify less parameters if you don't need them
+		// Unity allows to specify fewer parameters if you don't need them
 		const string test = @"
 using UnityEngine;
 
@@ -381,4 +381,32 @@ static async Awaitable<bool> OnPreGeneratingCSProjectFiles()
 		await VerifyCSharpFixAsync(test, fixedTest);
 	}
 
+	[Fact]
+	public async Task BadMessageSignatureWithUsedMethod()
+	{
+		const string test = @"
+using UnityEditor;
+
+class Camera : Editor
+{
+    private void Foo()
+    {
+        OnSceneGUI(null);
+    }
+
+    private void OnSceneGUI(object foo)
+    {
+    }
+}
+";
+
+		var diagnostic = ExpectDiagnostic()
+			.WithLocation(11, 18)
+			.WithArguments("OnSceneGUI");
+
+		await VerifyCSharpDiagnosticAsync(test, diagnostic);
+
+		// In this special case, we do not provide a codefix, given it would break the code as the message is -wrongly- used elsewhere
+		await VerifyCSharpFixAsync(test, test);
+	}
 }

src/Microsoft.Unity.Analyzers/CodeFixContextExtensions.cs

@@ -8,6 +8,7 @@
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CodeFixes;
+using Microsoft.CodeAnalysis.FindSymbols;
 
 namespace Microsoft.Unity.Analyzers;
 
@@ -31,4 +32,18 @@ internal static class CodeFixContextExtensions
 			.OfType<T>()
 			.FirstOrDefault(predicate);
 	}
+
+	public static async Task<bool> IsReferencedAsync(this CodeFixContext context, SyntaxNode declaration)
+	{
+		var semanticModel = await context.Document
+			.GetSemanticModelAsync(context.CancellationToken)
+			.ConfigureAwait(false);
+
+		var symbol = semanticModel?.GetDeclaredSymbol(declaration);
+		if (symbol == null)
+			return false;
+
+		var references = await SymbolFinder.FindReferencesAsync(symbol, context.Document.Project.Solution, context.CancellationToken);
+		return references.Any(r => r.Locations.Any());
+	}
 }

src/Microsoft.Unity.Analyzers/MessageSignature.cs

@@ -100,14 +100,18 @@ public class MessageSignatureCodeFix : CodeFixProvider
 
 	public sealed override async Task RegisterCodeFixesAsync(CodeFixContext context)
 	{
-		var methodDeclaration = await context.GetFixableNodeAsync<MethodDeclarationSyntax>();
-		if (methodDeclaration == null)
+		var method = await context.GetFixableNodeAsync<MethodDeclarationSyntax>();
+		if (method == null)
+			return;
+
+		// Do not provide a code fix if the message is -wrongly- referenced elsewhere
+		if (await context.IsReferencedAsync(method))
 			return;
 
 		context.RegisterCodeFix(
 			CodeAction.Create(
 				Strings.MessageSignatureCodeFixTitle,
-				ct => FixMethodDeclarationSignatureAsync(context.Document, methodDeclaration, ct),
+				ct => FixMethodDeclarationSignatureAsync(context.Document, method, ct),
 				FixableDiagnosticIds.Single()), // using DiagnosticId as equivalence key for BatchFixer
 			context.Diagnostics);
 	}