Add USP0020 - The Unity runtime invokes Unity messages (#273)

doc/USP0020.md

@@ -0,0 +1,33 @@
+# USP0020 The Unity runtime invokes Unity messages
+
+Unity messages should not be flagged as unused because Unity invokes those messages.
+
+## Suppressed Diagnostic ID
+
+IDE0052 - Private method can be removed as it is never invoked.
+
+## Examples of code that produces a suppressed diagnostic
+```csharp
+using UnityEngine;
+
+class Camera : MonoBehaviour
+{
+	void Start()
+	{
+		//Some code
+	}
+
+	/// <summary>
+	/// This reference triggers IDE0052 <see cref=""Start"" />
+	/// </summary>
+	public float speed = 0f;
+}
+```
+
+## Why is the diagnostic reported?
+
+The IDE cannot find any references to the method `Start` and believes it to be unused.
+
+## Why do we suppress this diagnostic?
+
+Even though the IDE cannot find any references to `Start`, it will be called by Unity, and should not be removed.

doc/index.md

@@ -59,3 +59,4 @@ ID | Suppressed ID | Justification
 [USP0017](USP0017.md) | IDE0074 | Unity objects should not use coalescing assignment
 [USP0018](USP0018.md) | IDE0016 | Unity objects should not be used with throw expressions
 [USP0019](USP0012.md) | IDE0051 | Don't flag private methods with PreserveAttribute or UsedImplicitlyAttribute as unused
+[USP0003](USP0020.md) | IDE0052 | The Unity runtime invokes Unity messages

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

@@ -53,6 +53,31 @@ private void Start()
 		await VerifyCSharpDiagnosticAsync(test, suppressor);
 	}
 
+	[Fact]
+	public async Task UnusedMethodWithCrefSuppressed()
+	{
+		const string test = @"
+using UnityEngine;
+
+public class TestScript : MonoBehaviour
+{
+    private void Start()
+    {
+    }
+
+	/// <summary>
+	/// IDE0052 should be suppressed <see cref=""Start"" />
+	/// </summary>
+	public float speed = 0f;
+}
+";
+
+		var suppressor = ExpectSuppressor(MessageSuppressor.MethodCrefRule)
+			.WithLocation(6, 18);
+
+		await VerifyCSharpDiagnosticAsync(test, suppressor);
+	}
+
 	[Fact]
 	public async Task UnusedParameterSuppressed()
 	{

src/Microsoft.Unity.Analyzers/MessageSuppressor.cs

@@ -20,6 +20,11 @@ public class MessageSuppressor : DiagnosticSuppressor
 		suppressedDiagnosticId: "IDE0051",
 		justification: Strings.MessageSuppressorJustification);
 
+	internal static readonly SuppressionDescriptor MethodCrefRule = new(
+		id: "USP0020",
+		suppressedDiagnosticId: "IDE0052",
+		justification: Strings.MessageSuppressorJustification);
+
 	internal static readonly SuppressionDescriptor MethodCodeQualityRule = new(
 		id: "USP0014",
 		suppressedDiagnosticId: "CA1822",
@@ -36,7 +41,7 @@ public class MessageSuppressor : DiagnosticSuppressor
 		suppressedDiagnosticId: "CA1801",
 		justification: Strings.MessageSuppressorJustification);
 
-	public override ImmutableArray<SuppressionDescriptor> SupportedSuppressions => ImmutableArray.Create(MethodRule, MethodCodeQualityRule, ParameterRule, ParameterCodeQualityRule);
+	public override ImmutableArray<SuppressionDescriptor> SupportedSuppressions => ImmutableArray.Create(MethodRule, MethodCrefRule, MethodCodeQualityRule, ParameterRule, ParameterCodeQualityRule);
 
 	public override void ReportSuppressions(SuppressionAnalysisContext context)
 	{