Improve RCS1097

ChangeLog.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 - Add SECURITY.md ([#1147](https://github.com/josefpihrt/roslynator/pull/1147))
+- 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

@@ -64,10 +64,30 @@ 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)
                 {
-                    return true;
+                    case InterpolationSyntax:
+                        {
+                            if (IsNotHidden(methodSymbol, containingType))
+                                return true;
+
+                            break;
+                        }
+                    case BinaryExpressionSyntax { RawKind: (int)SyntaxKind.AddExpression } addExpression:
+                        {
+                            if (addExpression.Right == expression
+                                && semanticModel.GetTypeInfo(addExpression.Left, cancellationToken).Type?.SpecialType == SpecialType.System_String)
+                                return true;
+
+                            if (addExpression.Left == expression
+                                && semanticModel.GetTypeInfo(addExpression.Right, cancellationToken).Type?.SpecialType == SpecialType.System_String
+                                && (addExpression.Right.WalkDownParentheses() is not InvocationExpressionSyntax invocationExpression2
+                                    || semanticModel.GetMethodSymbol(invocationExpression2, cancellationToken).Name != "ToString"))
+                                return true;
+
+                            break;
+                        }
                 }
             }
         }

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()
     {