bugfix: improve CollectionShouldHaveElementAt_IndexerShouldBe detection (#390)

Author: Meir017

src/FluentAssertions.Analyzers.TestUtils/GenerateCode.cs

@@ -55,7 +55,9 @@ public static string GenericIListExpressionBodyAssertion(string assertion) => Ge
             .AppendLine("    {")
             .AppendLine("        public bool BooleanProperty { get; set; }")
             .AppendLine("        public string Message { get; set; }")
+            .AppendLine("        public TestComplexClass this[int index] => throw new NotImplementedException();")
             .AppendLine("    }")
+            .AppendLine()
             .AppendLine("}")
             .ToString();
 

src/FluentAssertions.Analyzers.Tests/Tips/CollectionTests.cs

@@ -773,7 +773,7 @@ public void CollectionShouldContainSingle_TestAnalyzer_GenericIEnumerableShouldR
         [AssertionDiagnostic("actual.ElementAt(k).BooleanProperty.Should().Be(expectedItem.BooleanProperty{0});")]
         [AssertionDiagnostic("actual.ElementAt(6).BooleanProperty.Should().Be(expectedItem.BooleanProperty{0});")]
         [AssertionDiagnostic("actual.AsEnumerable().ElementAt(k).BooleanProperty.Should().Be(expectedItem.BooleanProperty{0}).And.ToString();")]
-        [AssertionDiagnostic("actual.AsEnumerable().ElementAt(6).BooleanProperty.Should().Be(expectedItem.BooleanProperty{0}).And.ToString();")] 
+        [AssertionDiagnostic("actual.AsEnumerable().ElementAt(6).BooleanProperty.Should().Be(expectedItem.BooleanProperty{0}).And.ToString();")]
         [Implemented]
         public void CollectionShouldHaveElementAt_ElementAtIndexShouldBe_TestNoAnalyzer(string assertion) => DiagnosticVerifier.VerifyCSharpDiagnosticUsingAllAnalyzers(GenerateCode.GenericIListCodeBlockAssertion(assertion));
 
@@ -793,6 +793,11 @@ public void CollectionShouldContainSingle_TestAnalyzer_GenericIEnumerableShouldR
         [Implemented]
         public void CollectionShouldHaveElementAt_IndexerShouldBe_TestAnalyzer(string assertion) => VerifyCSharpDiagnosticCodeBlock(assertion, DiagnosticMetadata.CollectionShouldHaveElementAt_IndexerShouldBe);
 
+        [DataTestMethod]
+        [AssertionDiagnostic("var first = actual[0]; first[6].Should().Be(expectedItem{0});")]
+        [Implemented]
+        public void CollectionShouldHaveElementAt_IndexerShouldBe_TestNoAnalyzer(string assertion) => DiagnosticVerifier.VerifyCSharpDiagnosticUsingAllAnalyzers(GenerateCode.GenericIListCodeBlockAssertion(assertion));
+
         [DataTestMethod]
         [AssertionDiagnostic("actual.Skip(k).First().Should().Be(expectedItem{0});")]
         [AssertionDiagnostic("actual.Skip(6).First().Should().Be(expectedItem{0});")]

src/FluentAssertions.Analyzers/Tips/FluentAssertionsAnalyzer.Utils.cs

@@ -70,6 +70,8 @@ public FluentAssertionsMetadata(Compilation compilation)
             IDictionaryOfT2 = compilation.GetTypeByMetadataName(typeof(IDictionary<,>).FullName);
             DictionaryOfT2 = compilation.GetTypeByMetadataName(typeof(Dictionary<,>).FullName);
             IReadonlyDictionaryOfT2 = compilation.GetTypeByMetadataName(typeof(IReadOnlyDictionary<,>).FullName);
+            IListOfT = compilation.GetTypeByMetadataName(typeof(IList<>).FullName);
+            IReadonlyListOfT = compilation.GetTypeByMetadataName(typeof(IReadOnlyList<>).FullName);
             Enumerable = compilation.GetTypeByMetadataName(typeof(Enumerable).FullName);
             IEnumerable = compilation.GetTypeByMetadataName(typeof(IEnumerable).FullName);
             Math = compilation.GetTypeByMetadataName(typeof(Math).FullName);
@@ -87,6 +89,8 @@ public FluentAssertionsMetadata(Compilation compilation)
         public INamedTypeSymbol IDictionaryOfT2 { get; }
         public INamedTypeSymbol DictionaryOfT2 { get; }
         public INamedTypeSymbol IReadonlyDictionaryOfT2 { get; }
+        public INamedTypeSymbol IListOfT { get; }
+        public INamedTypeSymbol IReadonlyListOfT { get; }
         public INamedTypeSymbol BooleanAssertionsOfT1 { get; }
         public INamedTypeSymbol NumericAssertionsOfT2 { get; }
         public INamedTypeSymbol Enumerable { get; }

src/FluentAssertions.Analyzers/Tips/FluentAssertionsAnalyzer.cs

@@ -394,6 +394,7 @@ private static void AnalyzeInvocation(OperationAnalysisContext context, FluentAs
                     }
                     else if (subject.TryGetFirstDescendent<IPropertyReferenceOperation>(out var propertyReference) && propertyReference.Property.IsIndexer)
                     {
+                        if (!propertyReference.Instance.Type.ImplementsOrIsInterface(metadata.IListOfT) && !propertyReference.Instance.Type.ImplementsOrIsInterface(metadata.IReadonlyListOfT)) return;
                         if (propertyReference.Instance.Type.ImplementsOrIsInterface(metadata.IDictionaryOfT2) || propertyReference.Instance.Type.ImplementsOrIsInterface(metadata.IReadonlyDictionaryOfT2)) return;
 
                         context.ReportDiagnostic(CreateDiagnostic(assertion, DiagnosticMetadata.CollectionShouldHaveElementAt_IndexerShouldBe));