From 9f10355a3f079298421cb8d39e0d681c0ab2ca1f Mon Sep 17 00:00:00 2001
From: James May <fowl2@users.noreply.github.com>
Date: Fri, 14 Feb 2025 11:43:12 +1100
Subject: [PATCH] fix false positive casting from value type constraint to Enum
 or ValueType #7031

---
 ...stOrOfTypeWithIncompatibleTypesAnalyzer.cs |  3 +-
 ...fTypeWithIncompatibleTypesAnalyzerTests.cs | 29 +++++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/src/NetAnalyzers/Core/Microsoft.NetCore.Analyzers/Runtime/DoNotCallEnumerableCastOrOfTypeWithIncompatibleTypesAnalyzer.cs b/src/NetAnalyzers/Core/Microsoft.NetCore.Analyzers/Runtime/DoNotCallEnumerableCastOrOfTypeWithIncompatibleTypesAnalyzer.cs
index bc3dda1329..0542458402 100644
--- a/src/NetAnalyzers/Core/Microsoft.NetCore.Analyzers/Runtime/DoNotCallEnumerableCastOrOfTypeWithIncompatibleTypesAnalyzer.cs
+++ b/src/NetAnalyzers/Core/Microsoft.NetCore.Analyzers/Runtime/DoNotCallEnumerableCastOrOfTypeWithIncompatibleTypesAnalyzer.cs
@@ -267,7 +267,8 @@ static bool IsUnconstrainedTypeParameter(ITypeParameterSymbol typeParameterSymbo
                         if (castToTypeParam.HasValueTypeConstraint
                             && castFrom.TypeKind == TypeKind.Class)
                         {
-                            return true;
+                            return castFrom.SpecialType is not SpecialType.System_Enum
+                                                       and not SpecialType.System_ValueType;
                         }
 
                         return false;
diff --git a/src/NetAnalyzers/UnitTests/Microsoft.NetCore.Analyzers/Runtime/DoNotCallEnumerableCastOrOfTypeWithIncompatibleTypesAnalyzerTests.cs b/src/NetAnalyzers/UnitTests/Microsoft.NetCore.Analyzers/Runtime/DoNotCallEnumerableCastOrOfTypeWithIncompatibleTypesAnalyzerTests.cs
index 7e6523ce82..23337eb425 100644
--- a/src/NetAnalyzers/UnitTests/Microsoft.NetCore.Analyzers/Runtime/DoNotCallEnumerableCastOrOfTypeWithIncompatibleTypesAnalyzerTests.cs
+++ b/src/NetAnalyzers/UnitTests/Microsoft.NetCore.Analyzers/Runtime/DoNotCallEnumerableCastOrOfTypeWithIncompatibleTypesAnalyzerTests.cs
@@ -910,6 +910,35 @@ class GenericDerived : GenericBase<int>
             await test.RunAsync();
         }
 
+        [Fact, WorkItem(7031, "https://github.com/dotnet/roslyn-analyzers/issues/7031")]
+        public async Task GenericValueType()
+        {
+            // ensure runtime behavior is matches
+            _ = new Enum[] { StringComparison.OrdinalIgnoreCase }.Cast<StringComparison>().ToArray();
+            _ = new ValueType[] { int.MaxValue }.Cast<int>().ToArray();
+
+            var test = new VerifyCS.Test
+            {
+                ReferenceAssemblies = ReferenceAssemblies.Net.Net90,
+                LanguageVersion = LanguageVersion.Latest,
+
+                TestCode = @"
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+public static class Program
+{
+    public static IEnumerable<T> CastEnums<T>(IEnumerable<Enum> values) where T : struct, Enum
+          => values.Cast<T>(); // CA2021
+
+    public static IEnumerable<T> CastValueTypes<T>(IEnumerable<ValueType> values) where T : struct
+          => values.Cast<T>(); // CA2021
+}"
+            };
+            await test.RunAsync();
+        }
+
         [Fact]
         public async Task NonGenericCasesVB()
         {