xunit/xunit#1258 Analyzer for uninitialized member data

src/xunit.analyzers.tests/Analyzers/X1000/MemberDataShouldReferenceValidMemberTests.cs

@@ -11,6 +11,7 @@ public class X1014_MemberDataShouldUseNameOfOperator
 		public async ValueTask V2_and_V3()
 		{
 			var source = /* lang=c#-test */ """
+				#pragma warning disable xUnit1053
 				using System.Collections.Generic;
 				using Xunit;
 
@@ -149,6 +150,7 @@ public class X1018_MemberDataMustReferenceValidMemberKind
 		public async ValueTask V2_and_V3()
 		{
 			var source = /* lang=c#-test */ """
+				#pragma warning disable xUnit1053
 				using System;
 				using System.Collections.Generic;
 				using Xunit;
@@ -196,6 +198,7 @@ public async ValueTask V2_and_V3()
 		{
 			var source = /* lang=c#-test */ """
 				#pragma warning disable xUnit1042
+				#pragma warning disable xUnit1053
 
 				using System;
 				using System.Collections.Generic;
@@ -319,6 +322,7 @@ public async ValueTask V3_only()
 		{
 			var source = /* lang=c#-test */ """
 				#pragma warning disable xUnit1042
+				#pragma warning disable xUnit1053
 
 				using System.Collections.Generic;
 				using System.Threading.Tasks;
@@ -371,6 +375,7 @@ public class X1020_MemberDataPropertyMustHaveGetter
 		public async ValueTask V2_and_V3()
 		{
 			var source = /* lang=c#-test */ """
+				#pragma warning disable xUnit1053
 				using Xunit;
 
 				public class TestClass {
@@ -399,6 +404,7 @@ public class X1021_MemberDataNonMethodShouldNotHaveParameters
 		public async ValueTask V2_and_V3()
 		{
 			var source = /* lang=c#-test */ """
+				#pragma warning disable xUnit1053
 				using Xunit;
 
 				public class TestClassBase {
@@ -1361,6 +1367,7 @@ public class X1042_MemberDataTheoryDataIsRecommendedForStronglyTypedAnalysis
 		public async ValueTask V2_and_V3()
 		{
 			var source = /* lang=c#-test */ """
+				#pragma warning disable xUnit1053
 				using System.Collections.Generic;
 				using Xunit;
 
@@ -1409,6 +1416,7 @@ public void TestMethod2(int _) { }
 		public async Task V3_only()
 		{
 			var source = /* lang=c#-test */ """
+				#pragma warning disable xUnit1053
 				using System.Collections.Generic;
 				using System.Threading.Tasks;
 				using Xunit;
@@ -1506,4 +1514,71 @@ public void TestMethod6(int _) { }
 			await Verify.VerifyAnalyzerV3(LanguageVersion.CSharp7_1, source, expected);
 		}
 	}
+
+	public class X1053_MemberDataMemberMustBeStaticallyWrittenTo
+	{
+		[Fact]
+		public async ValueTask Initializers_AndGetExpressions_MarkAsWrittenTo()
+		{
+			var source = /* lang=c#-test */ """
+				using Xunit;
+
+				public class TestClass {
+					public static TheoryData<int> Field = null;
+					public static TheoryData<int> Property { get; } = null;
+					public static TheoryData<int> PropertyWithGetBody { get { return null; } }
+					public static TheoryData<int> PropertyWithGetExpression => null;
+					public static TheoryData<int> FieldWrittenInStaticConstructor;
+					public static TheoryData<int> PropertyWrittenInStaticConstructor { get; set; }
+
+					static TestClass()
+					{
+						FieldWrittenInStaticConstructor = null;
+						PropertyWrittenInStaticConstructor = null;
+					}
+
+					[Theory]
+					[MemberData(nameof(Field))]
+					[MemberData(nameof(Property))]
+					[MemberData(nameof(PropertyWithGetBody))]
+					[MemberData(nameof(PropertyWithGetExpression))]
+					[MemberData(nameof(FieldWrittenInStaticConstructor))]
+					[MemberData(nameof(PropertyWrittenInStaticConstructor))]
+					public void TestCase(int _) {}
+				}
+			""";
+
+			await Verify.VerifyAnalyzer(source, []);
+		}
+
+		[Fact]
+		public async ValueTask SimpleCase_GeneratesResult()
+		{
+			var source = /* lang=c#-test */ """
+				using Xunit;
+
+				public class TestClass {
+					public static TheoryData<int> {|#0:Field|};
+					public static TheoryData<int> {|#1:Property|} { get; set; }
+
+					public TestClass()
+					{
+						Field = null;
+						Property = null;
+					}
+
+					[Theory]
+					[MemberData(nameof(Field)), MemberData(nameof(Property))]
+					public void TestCase(int _) {}
+				}
+			""";
+
+			var expected = new[] {
+				Verify.Diagnostic("xUnit1053").WithLocation(0).WithArguments("Field"),
+				Verify.Diagnostic("xUnit1053").WithLocation(1).WithArguments("Property"),
+			};
+
+			await Verify.VerifyAnalyzer(source, expected);
+		}
+	}
 }

src/xunit.analyzers.tests/Fixes/X1000/MemberDataShouldReferenceValidMember_NameOfFixerTests.cs

@@ -14,7 +14,7 @@ public async Task ConvertStringToNameOf()
 			using Xunit;
 
 			public class TestClass {
-				public static TheoryData<int> DataSource;
+				public static TheoryData<int> DataSource = new TheoryData<int>();
 
 				[Theory]
 				[MemberData({|xUnit1014:"DataSource"|})]
@@ -27,7 +27,7 @@ public void TestMethod(int a) { }
 			using Xunit;
 
 			public class TestClass {
-				public static TheoryData<int> DataSource;
+				public static TheoryData<int> DataSource = new TheoryData<int>();
 
 				[Theory]
 				[MemberData(nameof(DataSource))]

src/xunit.analyzers/Utility/Descriptors.xUnit1xxx.cs

@@ -483,7 +483,14 @@ public static partial class Descriptors
 			"'TheoryData<...>' should not be used with one or more type arguments that implement 'ITheoryDataRow' or a derived variant. This usage is not supported. Use either 'TheoryData' or a type of 'ITheoryDataRow' exclusively."
 		);
 
-	// Placeholder for rule X1053
+	public static DiagnosticDescriptor X1053_MemberDataMemberMustBeStaticallyWrittenTo { get; } =
+		Diagnostic(
+			"xUnit1053",
+			"The static member used as theory data must be statically initialized.",
+			Usage,
+			Warning,
+			"The member {0} referenced by MemberData is not initialized before use."
+		);
 
 	// Placeholder for rule X1054
 

src/xunit.analyzers/X1000/MemberDataShouldReferenceValidMember.cs

@@ -33,7 +33,8 @@ public MemberDataShouldReferenceValidMember() :
 			Descriptors.X1038_TheoryDataTypeArgumentsMustMatchTestMethodParameters_ExtraTypeParameters,
 			Descriptors.X1039_TheoryDataTypeArgumentsMustMatchTestMethodParameters_IncompatibleTypes,
 			Descriptors.X1040_TheoryDataTypeArgumentsMustMatchTestMethodParameters_IncompatibleNullability,
-			Descriptors.X1042_MemberDataTheoryDataIsRecommendedForStronglyTypedAnalysis
+			Descriptors.X1042_MemberDataTheoryDataIsRecommendedForStronglyTypedAnalysis,
+			Descriptors.X1053_MemberDataMemberMustBeStaticallyWrittenTo
 		)
 	{ }
 
@@ -137,6 +138,9 @@ public override void AnalyzeCompilation(
 				if (!memberSymbol.IsStatic)
 					ReportNonStatic(context, attributeSyntax, memberProperties);
 
+				if (!IsInitialized(memberSymbol, context))
+					ReportMemberMustBeWrittenTo(context, memberSymbol);
+
 				// Unwrap Task or ValueTask, but only for v3
 				if (xunitContext.HasV3References &&
 					memberReturnType is INamedTypeSymbol namedMemberReturnType &&
@@ -195,6 +199,50 @@ memberReturnType is INamedTypeSymbol namedMemberReturnType &&
 		}, SyntaxKind.MethodDeclaration);
 	}
 
+	static bool IsInitialized(
+		ISymbol memberSymbol,
+		SyntaxNodeAnalysisContext context
+	)
+	{
+		if (!memberSymbol.IsStatic || memberSymbol is IMethodSymbol)
+			// assume initialized, if nonstatic or method to avoid spurious results
+			return true;
+
+		var semantics = context.SemanticModel;
+		var declarationReference = memberSymbol.DeclaringSyntaxReferences.First();
+		var declarationSyntax = declarationReference.GetSyntax();
+		if (declarationSyntax is PropertyDeclarationSyntax prop
+			&& (prop.Initializer != null
+				|| prop.AccessorList?.Accessors.FirstOrDefault(decl => decl.Kind() == SyntaxKind.GetAccessorDeclaration)?.Body != null
+				|| prop.ExpressionBody != null))
+			return true;
+
+		if (declarationSyntax is VariableDeclaratorSyntax field
+			&& field.Initializer != null)
+			return true;
+
+		var declarationContainer = declarationSyntax.FirstAncestorOrSelf<TypeDeclarationSyntax>()!;
+		var staticConstructors = declarationContainer.DescendantNodes()
+			.OfType<ConstructorDeclarationSyntax>()
+			.Where(ctor => ctor.Modifiers.Any(SyntaxKind.StaticKeyword));
+
+		foreach (var ctor in staticConstructors)
+		{
+			// Look for direct assignments to the member
+			var assignments = ctor.DescendantNodes(descendIntoChildren: _ => true, descendIntoTrivia: false)
+				.OfType<AssignmentExpressionSyntax>()
+				.Where(assignment =>
+				{
+					var assignedSymbol = semantics.GetSymbolInfo(assignment.Left).Symbol;
+					return SymbolEqualityComparer.Default.Equals(assignedSymbol?.OriginalDefinition, memberSymbol);
+				});
+
+			if (assignments.Any())
+				return true;
+		}
+		return false;
+	}
+
 	static ISymbol? FindMemberSymbol(
 		string memberName,
 		ITypeSymbol? type,
@@ -528,6 +576,17 @@ static void ReportMissingMember(
 				)
 			);
 
+	static void ReportMemberMustBeWrittenTo(
+		SyntaxNodeAnalysisContext context,
+		ISymbol memberSymbol) =>
+			context.ReportDiagnostic(
+				Diagnostic.Create(
+					Descriptors.X1053_MemberDataMemberMustBeStaticallyWrittenTo,
+					memberSymbol.Locations.First(),
+					memberSymbol.Name
+				)
+			);
+
 	static void ReportNonPublicAccessibility(
 		SyntaxNodeAnalysisContext context,
 		AttributeSyntax attribute,