Improve RCS1097

ChangeLog.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Add SECURITY.md ([#1147](https://github.com/josefpihrt/roslynator/pull/1147))
 - Add custom FixAllProvider for [RCS1014](https://github.com/JosefPihrt/Roslynator/blob/main/docs/analyzers/RCS1014.md) ([#1070](https://github.com/JosefPihrt/Roslynator/pull/1070)).
+- Add more cases to [RCS1097](https://github.com/JosefPihrt/Roslynator/blob/main/docs/analyzers/RCS1097.md) ([#1160](https://github.com/JosefPihrt/Roslynator/pull/1160)).
 
 ### Fixed
 

src/Analyzers/CSharp/Analysis/RemoveRedundantToStringCallAnalysis.cs

@@ -48,12 +48,7 @@ public static void Analyze(SyntaxNodeAnalysisContext context, in SimpleMemberInv
 
         IMethodSymbol methodSymbol = semanticModel.GetMethodSymbol(invocationExpression, cancellationToken);
 
-        if (methodSymbol?.DeclaredAccessibility == Accessibility.Public
-            && !methodSymbol.IsStatic
-            && !methodSymbol.IsGenericMethod
-            && string.Equals(methodSymbol.Name, "ToString", StringComparison.Ordinal)
-            && methodSymbol.ReturnType.SpecialType == SpecialType.System_String
-            && !methodSymbol.Parameters.Any())
+        if (IsToString(methodSymbol))
         {
             INamedTypeSymbol containingType = methodSymbol.ContainingType;
 
@@ -64,15 +59,38 @@ public static void Analyze(SyntaxNodeAnalysisContext context, in SimpleMemberInv
                 if (containingType.SpecialType == SpecialType.System_String)
                     return true;
 
-                if (invocationExpression.WalkUpParentheses().IsParentKind(SyntaxKind.Interpolation)
-                    && IsNotHidden(methodSymbol, containingType))
+                ExpressionSyntax expression = invocationExpression.WalkUpParentheses();
+                switch (expression.Parent.Kind())
                 {
-                    return true;
+                    case SyntaxKind.Interpolation:
+                        {
+                            return IsNotHidden(methodSymbol, containingType);
+                        }
+                    case SyntaxKind.AddExpression:
+                        {
+                            var addExpression = (BinaryExpressionSyntax)expression.Parent;
+                            if (addExpression.Right == expression)
+                                return semanticModel.GetTypeInfo(addExpression.Left, cancellationToken).Type?.SpecialType == SpecialType.System_String;
+
+                            return semanticModel.GetTypeInfo(addExpression.Right, cancellationToken).Type?.SpecialType == SpecialType.System_String
+                                && (addExpression.Right.WalkDownParentheses() is not InvocationExpressionSyntax invocationExpression2
+                                    || !IsToString(semanticModel.GetMethodSymbol(invocationExpression2, cancellationToken)));
+                        }
                 }
             }
         }
 
         return false;
+
+        static bool IsToString(IMethodSymbol methodSymbol)
+        {
+            return methodSymbol?.DeclaredAccessibility == Accessibility.Public
+                && !methodSymbol.IsStatic
+                && !methodSymbol.IsGenericMethod
+                && string.Equals(methodSymbol.Name, "ToString", StringComparison.Ordinal)
+                && methodSymbol.ReturnType.SpecialType == SpecialType.System_String
+                && !methodSymbol.Parameters.Any();
+        }
     }
 
     private static bool IsNotHidden(IMethodSymbol methodSymbol, INamedTypeSymbol containingType)

src/Tests/Analyzers.Tests/RCS1097RemoveRedundantToStringCallTests.cs

@@ -80,6 +80,32 @@ void M()
 ");
     }
 
+    [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.RemoveRedundantToStringCall)]
+    public async Task Test_PlusString()
+    {
+        await VerifyDiagnosticAndFixAsync(@"
+class C
+{
+    void M(object o)
+    {
+        string s = """" + o[|.ToString()|];
+        string s2 = o[|.ToString()|] + """";
+        string s3 = o.ToString() + o[|.ToString()|];
+    }
+}
+", @"
+class C
+{
+    void M(object o)
+    {
+        string s = """" + o;
+        string s2 = o + """";
+        string s3 = o.ToString() + o;
+    }
+}
+");
+    }
+
     [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.RemoveRedundantToStringCall)]
     public async Task Test_Interpolation()
     {