Merge pull request #7493 from dotnet/fix/enumerable-casts/7357-9.0.1xx

[Backport] Fix CA2021 false positive for generic class types

src/NetAnalyzers/Core/Microsoft.NetCore.Analyzers/Runtime/DoNotCallEnumerableCastOrOfTypeWithIncompatibleTypesAnalyzer.cs

@@ -196,6 +196,10 @@ static bool CastWillAlwaysFail(ITypeSymbol castFrom, ITypeSymbol castTo)
                     return false;
                 }
 
+                // Most checks are better with OriginalDefinition, but keep the ones passed in around.
+                ITypeSymbol castFromParam = castFrom;
+                ITypeSymbol castToParam = castTo;
+
                 castFrom = castFrom.OriginalDefinition;
                 castTo = castTo.OriginalDefinition;
 
@@ -269,8 +273,8 @@ static bool IsUnconstrainedTypeParameter(ITypeParameterSymbol typeParameterSymbo
                         return false;
 
                     case (TypeKind.Class, TypeKind.Class):
-                        return !castFrom.DerivesFrom(castTo)
-                            && !castTo.DerivesFrom(castFrom);
+                        return !castFromParam.DerivesFrom(castToParam)
+                            && !castToParam.DerivesFrom(castFromParam);
 
                     case (TypeKind.Interface, TypeKind.Class):
                         return castTo.IsSealed && !castTo.DerivesFrom(castFrom);

src/NetAnalyzers/UnitTests/Microsoft.NetCore.Analyzers/Runtime/DoNotCallEnumerableCastOrOfTypeWithIncompatibleTypesAnalyzerTests.cs

@@ -866,6 +866,50 @@ public sealed record class DataNodeUpdate(DataNode Updated) : NodeUpdate<DataNod
             await test.RunAsync();
         }
 
+        [Fact, WorkItem(7357, "https://github.com/dotnet/roslyn-analyzers/issues/7357")]
+        public async Task GenericDerivedType()
+        {
+            var test = new VerifyCS.Test
+            {
+                ReferenceAssemblies = ReferenceAssemblies.Net.Net70,
+                LanguageVersion = LanguageVersion.CSharp10,
+                TestCode = @"
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+
+public static class Program
+{
+    public static void Main()
+    {
+        // works as expected
+        new List<Base>() { new Derived() }.Cast<Derived>().ToList();
+
+        // same code but generic, fails
+        // CastTest\Program.cs(7,1,7,77): warning CA2021: Type 'GenericBase<int>' is incompatible with type 'GenericDerived' and cast attempts will throw InvalidCastException at runtime (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca2021)
+        new List<GenericBase<int>>() { new GenericDerived() }.Cast<GenericDerived>().ToList();
+    }
+}
+
+class Base
+{
+}
+
+class Derived : Base
+{
+}
+
+class GenericBase<T>
+{
+}
+
+class GenericDerived : GenericBase<int>
+{
+}"
+            };
+            await test.RunAsync();
+        }
+
         [Fact]
         public async Task NonGenericCasesVB()
         {