Fix RCS1084 (#1085)

Co-authored-by: Josef Pihrt <josef.pihrt@outlook.com>
dotnet · Jun 1, 2023 · 31bf7e7 · 31bf7e7
1 parent ee6668f
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diff --git a/ChangeLog.md b/ChangeLog.md
@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Improve inversion of logical expressions to handling additional cases ([#1086](https://github.com/josefpihrt/roslynator/pull/1086)).
+- Fix [RCS1084](https://github.com/JosefPihrt/Roslynator/blob/main/docs/analyzers/RCS1084.md) ([#1085](https://github.com/josefpihrt/roslynator/pull/1085)).
 
 ## [4.3.0] - 2023-04-24
 

diff --git a/src/Analyzers.CodeFixes/CSharp/Refactorings/SimplifyNullCheckRefactoring.cs b/src/Analyzers.CodeFixes/CSharp/Refactorings/SimplifyNullCheckRefactoring.cs
@@ -44,6 +44,25 @@ public static async Task<Document> RefactorAsync(
  //RCS1084 UseCoalesceExpressionInsteadOfConditionalExpression
  newNode = nullCheck.Expression;
  coalesce = true;
+
+ // If the types are polymorphic then the LHS of the null coalesce must be cast to the base type.
+ ITypeSymbol newNodeType = semanticModel.GetTypeSymbol(newNode);
+ ITypeSymbol whenNullType = semanticModel.GetTypeSymbol(whenNull);
+ ITypeSymbol overallType = semanticModel.GetTypeInfo(conditionalExpression).ConvertedType;
+
+ if (overallType?.SupportsExplicitDeclaration() == true
+ && !SymbolEqualityComparer.Default.Equals(newNodeType, whenNullType))
+ {
+ TypeSyntax castType = overallType.ToTypeSyntax().WithSimplifierAnnotation();
+
+ if ((semanticModel.GetNullableContext(conditionalExpression.SpanStart) & NullableContext.AnnotationsEnabled) != 0)
+ castType = NullableType(castType);
+
+ newNode = CastExpression(
+ castType,
+ newNode.WithoutTrivia())
+ .WithTriviaFrom(newNode);
+ }
  }
  else if (semanticModel
  .GetTypeSymbol(nullCheck.Expression, cancellationToken)

diff --git a/src/Tests/Analyzers.Tests/RCS1084UseCoalesceExpressionInsteadOfConditionalExpressionTests.cs b/src/Tests/Analyzers.Tests/RCS1084UseCoalesceExpressionInsteadOfConditionalExpressionTests.cs
@@ -31,6 +31,88 @@ void M()
 }
 ", source, expected);
  }
+
+ [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.UseCoalesceExpressionInsteadOfConditionalExpression)]
+ public async Task Test_PolymorphicType_WithNullable()
+ {
+ await VerifyDiagnosticAndFixAsync(@"
+#nullable enable
+class C
+{
+ private interface IBase { }
+
+ private class A: IBase { }
+ 
+ private class B: IBase { }
+ 
+
+ void M()
+ {
+ A? a = null;
+
+ IBase c = [|a != null ? a : new B()|];
+ }
+}
+",@"
+#nullable enable
+class C
+{
+ private interface IBase { }
+
+ private class A: IBase { }
+ 
+ private class B: IBase { }
+ 
+
+ void M()
+ {
+ A? a = null;
+
+ IBase c = (IBase?)a ?? new B();
+ }
+}
+");
+ }
+
+ [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.UseCoalesceExpressionInsteadOfConditionalExpression)]
+ public async Task Test_PolymorphicType()
+ {
+ await VerifyDiagnosticAndFixAsync(@"
+class C
+{
+ private interface IBase { }
+
+ private class A: IBase { }
+ 
+ private class B: IBase { }
+ 
+
+ void M()
+ {
+ A a = null;
+
+ IBase c = [|a != null ? a : new B()|];
+ }
+}
+",@"
+class C
+{
+ private interface IBase { }
+
+ private class A: IBase { }
+ 
+ private class B: IBase { }
+ 
+
+ void M()
+ {
+ A a = null;
+
+ IBase c = (IBase)a ?? new B();
+ }
+}
+");
+ }
 
  [Theory, Trait(Traits.Analyzer, DiagnosticIdentifiers.UseCoalesceExpressionInsteadOfConditionalExpression)]
  [InlineData("(ni != null) ? ni.Value : 1", "ni ?? 1")]