Do not simplify default expression (RCS1244) (dotnet#966)

Haarmees · Oct 30, 2023 · 96514c9 · 96514c9
1 parent 44077d6
commit 96514c9
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Showing 3 changed files with 41 additions and 13 deletions.
diff --git a/ChangeLog.md b/ChangeLog.md
@@ -34,6 +34,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fix formatting of argument list ([#952](https://github.com/josefpihrt/roslynator/pull/952).
 - Do not remove async/await when 'using declaration' is used ([#953](https://github.com/josefpihrt/roslynator/pull/953).
 - Convert if-else to return statement when pattern matching is used ([RCS1073](https://github.com/JosefPihrt/Roslynator/blob/main/docs/analyzers/RCS1073.md)) ([#956](https://github.com/josefpihrt/roslynator/pull/956).
+- Do not simplify 'default' expression if the type is inferred ([RCS1244](https://github.com/JosefPihrt/Roslynator/blob/main/docs/analyzers/1244.md)) ([#956](https://github.com/josefpihrt/roslynator/pull/966).
 
 -----
 <!-- Content below does not adhere to 'Keep a Changelog' format -->

diff --git a/src/Analyzers/CSharp/Analysis/DefaultExpressionAnalyzer.cs b/src/Analyzers/CSharp/Analysis/DefaultExpressionAnalyzer.cs
@@ -209,28 +209,38 @@ private static bool IsTypeInferredFromDefaultExpression2(
             {
                 SyntaxNode node = ((ExpressionSyntax)anonymousFunction).WalkUpParentheses().Parent;
 
-                if (node is ArgumentSyntax argument
-                    && node.IsParentKind(SyntaxKind.ArgumentList)
-                    && node.Parent.IsParentKind(SyntaxKind.InvocationExpression)
-                    && !IsGenericInvocation((InvocationExpressionSyntax)node.Parent.Parent))
+                if (node is ArgumentSyntax argument)
                 {
-                    IParameterSymbol parameterSymbol = context.SemanticModel.DetermineParameter(argument);
-
-                    if (parameterSymbol?.OriginalDefinition.Type is INamedTypeSymbol namedTypeSymbol)
+                    if (node.IsParentKind(SyntaxKind.ArgumentList)
+                        && node.Parent.IsParentKind(SyntaxKind.InvocationExpression)
+                        && !IsGenericInvocation((InvocationExpressionSyntax)node.Parent.Parent))
                     {
-                        ITypeParameterSymbol typeParameterSymbol = namedTypeSymbol.TypeParameters.LastOrDefault();
+                        IParameterSymbol parameterSymbol = context.SemanticModel.DetermineParameter(argument);
 
-                        if (typeParameterSymbol != null
-                            && parameterSymbol.ContainingSymbol.OriginalDefinition is IMethodSymbol methodSymbol2)
+                        if (parameterSymbol?.OriginalDefinition.Type is INamedTypeSymbol namedTypeSymbol)
                         {
-                            foreach (ITypeParameterSymbol typeParameterSymbol2 in methodSymbol2.TypeParameters)
+                            ITypeParameterSymbol typeParameterSymbol = namedTypeSymbol.TypeParameters.LastOrDefault();
+
+                            if (typeParameterSymbol != null
+                                && parameterSymbol.ContainingSymbol.OriginalDefinition is IMethodSymbol methodSymbol2)
                             {
-                                if (string.Equals(typeParameterSymbol.Name, typeParameterSymbol2.Name, StringComparison.Ordinal))
-                                    return true;
+                                foreach (ITypeParameterSymbol typeParameterSymbol2 in methodSymbol2.TypeParameters)
+                                {
+                                    if (string.Equals(typeParameterSymbol.Name, typeParameterSymbol2.Name, StringComparison.Ordinal))
+                                        return true;
+                                }
                             }
                         }
                     }
                 }
+                else if (node is EqualsValueClauseSyntax)
+                {
+                    if (node.IsParentKind(SyntaxKind.VariableDeclarator)
+                        && node.Parent.Parent is VariableDeclarationSyntax variableDeclaration)
+                    {
+                        return variableDeclaration.Type.IsVar;
+                    }
+                }
             }
 
             return false;

diff --git a/src/Tests/Analyzers.Tests/RCS1244SimplifyDefaultExpressionTests.cs b/src/Tests/Analyzers.Tests/RCS1244SimplifyDefaultExpressionTests.cs
@@ -473,6 +473,23 @@ void M()
         _ = default(C) == 0;
     }
 }
+");
+        }
+
+        [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.SimplifyDefaultExpression)]
+        public async Task TestNoDiagnostic_LambdaExpression()
+        {
+            await VerifyNoDiagnosticAsync(@"
+class C
+{
+    void M()
+    {
+        var x = () =>
+        {
+            return default(object);
+        };
+    }
+}
 ");
         }
     }