MA0053 takes ctor visibility into account to determine if a class should be sealed (#815)

Author: meziantou

src/Meziantou.Analyzer/Rules/ClassMustBeSealedAnalyzer.cs

@@ -1,4 +1,4 @@
-using System.Collections.Generic;
+using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Linq;
 using System.Threading;
@@ -113,9 +113,11 @@ private bool IsPotentialSealed(AnalyzerOptions options, INamedTypeSymbol symbol,
             if (symbol.GetMembers().Any(member => member.IsVirtual) && !SealedClassWithVirtualMember(options, symbol))
                 return false;
 
-            if (symbol.IsVisibleOutsideOfAssembly() && !PublicClassShouldBeSealed(options, symbol))
+            var canBeInheritedOutsideOfAssembly = symbol.IsVisibleOutsideOfAssembly() && symbol.GetMembers().OfType<IMethodSymbol>().Where(member => member.MethodKind is MethodKind.Constructor).Any(member => member.IsVisibleOutsideOfAssembly());
+            if (canBeInheritedOutsideOfAssembly && !PublicClassShouldBeSealed(options, symbol))
                 return false;
 
+
             return true;
         }
 

tests/Meziantou.Analyzer.Test/Rules/ClassMustBeSealedAnalyzerTests.cs

@@ -1,4 +1,4 @@
-using System.Threading.Tasks;
+using System.Threading.Tasks;
 using Meziantou.Analyzer.Rules;
 using TestHelper;
 using Xunit;
@@ -256,6 +256,72 @@ internal sealed record Sample();
               .ValidateAsync();
     }
 
+    [Theory]
+    [InlineData("private")]
+    [InlineData("internal")]
+    [InlineData("private protected")]
+    public async Task ClassWithPrivateCtor(string visibility)
+    {
+        await CreateProjectBuilder()
+              .WithSourceCode($$"""
+                public class [||]Sample
+                {
+                    {{visibility}} Sample() { }
+                }
+                """)
+              .ValidateAsync();
+    }
+
+    [Theory]
+    [InlineData("private")]
+    [InlineData("internal")]
+    [InlineData("private protected")]
+    public async Task ClassWithMultiplePrivateCtors(string visibility)
+    {
+        await CreateProjectBuilder()
+              .WithSourceCode($$"""
+                public class [||]Sample
+                {
+                    private Sample(int a) { }
+                    {{visibility}} Sample() { }
+                }
+                """)
+              .ValidateAsync();
+    }
+
+    [Theory]
+    [InlineData("public")]
+    [InlineData("protected")]
+    [InlineData("protected internal")]
+    public async Task ClassWithPublicCtor(string visibility)
+    {
+        await CreateProjectBuilder()
+              .WithSourceCode($$"""
+                public class Sample
+                {
+                    {{visibility}} Sample() { }
+                }
+                """)
+              .ValidateAsync();
+    }
+
+    [Theory]
+    [InlineData("public")]
+    [InlineData("protected")]
+    [InlineData("protected internal")]
+    public async Task ClassWithPrivateAndPublicCtor(string visibility)
+    {
+        await CreateProjectBuilder()
+              .WithSourceCode($$"""
+                public class Sample
+                {
+                    private Sample(int a) { }
+                    {{visibility}} Sample() { }
+                }
+                """)
+              .ValidateAsync();
+    }
+
 #if CSHARP10_OR_GREATER
     [Fact]
     public async Task TopLevelStatement_10()