ignore capacity related diagnostics for system collection types when mapping from custom type

src/Riok.Mapperly/Descriptors/Enumerables/Capacity/CapacitySetterBuilder.cs

@@ -1,4 +1,5 @@
 using Microsoft.CodeAnalysis;
+using Riok.Mapperly.Symbols.Members;
 
 namespace Riok.Mapperly.Descriptors.Enumerables.Capacity;
 
@@ -48,7 +49,7 @@ bool includeTargetCount
         return new NonEnumeratedCapacitySetter(capacitySetter, targetCount, nonEnumeratedCountMethod);
     }
 
-    private static ICapacityMemberSetter? BuildCapacitySetter(MappingBuilderContext ctx, CollectionInfo target)
+    private static IMemberSetter? BuildCapacitySetter(MappingBuilderContext ctx, CollectionInfo target)
     {
         var ensureCapacityMethod = ctx
             .SymbolAccessor.GetAllMethods(target.Type, EnsureCapacityMethodSetter.EnsureCapacityMethodName)
@@ -58,7 +59,7 @@ bool includeTargetCount
 
         var member = ctx.SymbolAccessor.GetMappableMember(target.Type, CapacityMemberName);
         if (member is { CanSetDirectly: true, IsInitOnly: false, Type.SpecialType: SpecialType.System_Int32 })
-            return CapacityMemberSetter.Build(ctx, member);
+            return member.BuildSetter(ctx.UnsafeAccessorContext);
 
         return null;
     }

src/Riok.Mapperly/Descriptors/Enumerables/Capacity/EnsureCapacityMethodSetter.cs

@@ -7,7 +7,7 @@ namespace Riok.Mapperly.Descriptors.Enumerables.Capacity;
 /// <summary>
 /// Ensures the capacity of a collection by calling `EnsureCapacity(int)`
 /// </summary>
-internal class EnsureCapacityMethodSetter : ICapacityMemberSetter
+internal class EnsureCapacityMethodSetter : IMemberSetter
 {
     public static readonly EnsureCapacityMethodSetter Instance = new();
 
@@ -17,8 +17,6 @@ private EnsureCapacityMethodSetter() { }
 
     public bool SupportsCoalesceAssignment => false;
 
-    public IMappableMember? TargetCapacity => null;
-
     public ExpressionSyntax BuildAssignment(ExpressionSyntax? baseAccess, ExpressionSyntax valueToAssign, bool coalesceAssignment = false)
     {
         if (baseAccess == null)

src/Riok.Mapperly/Descriptors/Enumerables/Capacity/ICapacitySetter.cs

@@ -1,6 +1,5 @@
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Riok.Mapperly.Descriptors.Mappings;
-using Riok.Mapperly.Symbols.Members;
 
 namespace Riok.Mapperly.Descriptors.Enumerables.Capacity;
 
@@ -9,7 +8,5 @@ namespace Riok.Mapperly.Descriptors.Enumerables.Capacity;
 /// </summary>
 public interface ICapacitySetter
 {
-    IMappableMember? CapacityTargetMember { get; }
-
     StatementSyntax Build(TypeMappingBuildContext ctx, ExpressionSyntax target);
 }

src/Riok.Mapperly/Descriptors/Enumerables/Capacity/NonEnumeratedCapacitySetter.cs

@@ -18,16 +18,11 @@ namespace Riok.Mapperly.Descriptors.Enumerables.Capacity;
 ///     target.EnsureCapacity(sourceCount + target.Count);
 /// </code>
 /// </remarks>
-public class NonEnumeratedCapacitySetter(
-    ICapacityMemberSetter capacitySetter,
-    IMemberGetter? targetAccessor,
-    IMethodSymbol getNonEnumeratedMethod
-) : ICapacitySetter
+public class NonEnumeratedCapacitySetter(IMemberSetter capacitySetter, IMemberGetter? targetAccessor, IMethodSymbol getNonEnumeratedMethod)
+    : ICapacitySetter
 {
     private const string SourceCountVariableName = "sourceCount";
 
-    public IMappableMember? CapacityTargetMember => capacitySetter.TargetCapacity;
-
     public StatementSyntax Build(TypeMappingBuildContext ctx, ExpressionSyntax target)
     {
         var sourceCountName = ctx.NameBuilder.New(SourceCountVariableName);

src/Riok.Mapperly/Descriptors/Enumerables/Capacity/SimpleCapacitySetter.cs

@@ -15,11 +15,9 @@ namespace Riok.Mapperly.Descriptors.Enumerables.Capacity;
 /// target.Capacity = source.Length + target.Count;
 /// </code>
 /// </remarks>
-public class SimpleCapacitySetter(ICapacityMemberSetter capacitySetter, IMemberGetter? targetAccessor, IMemberGetter sourceAccessor)
+public class SimpleCapacitySetter(IMemberSetter capacitySetter, IMemberGetter? targetAccessor, IMemberGetter sourceAccessor)
     : ICapacitySetter
 {
-    public IMappableMember? CapacityTargetMember => capacitySetter.TargetCapacity;
-
     public StatementSyntax Build(TypeMappingBuildContext ctx, ExpressionSyntax target)
     {
         var count = sourceAccessor.BuildAccess(ctx.Source);

src/Riok.Mapperly/Descriptors/MappingBodyBuilders/BuilderContext/IMembersBuilderContext.cs

@@ -16,6 +16,7 @@ public interface IMembersBuilderContext<out T>
     MappingBuilderContext BuilderContext { get; }
 
     void IgnoreMembers(IMappableMember member);
+    void IgnoreMembers(string memberName);
 
     void SetMembersMapped(MemberMappingInfo members);
 

src/Riok.Mapperly/Descriptors/MappingBodyBuilders/BuilderContext/MembersMappingBuilderContext.cs

@@ -45,6 +45,8 @@ protected void SetTargetMemberMapped(string targetMemberName, bool ignoreCase =
 
     public void IgnoreMembers(IMappableMember member) => _state.IgnoreMembers(member);
 
+    public void IgnoreMembers(string memberName) => _state.IgnoreMembers(memberName);
+
     public void ConsumeMemberConfigs(MemberMappingInfo members)
     {
         if (members.Configuration != null)

src/Riok.Mapperly/Descriptors/MappingBodyBuilders/BuilderContext/MembersMappingState.cs

@@ -91,15 +91,17 @@ public void MappingAdded(MemberMappingInfo info, bool ignoreTargetCasing)
         SetMembersMapped(info, ignoreTargetCasing);
     }
 
-    public void IgnoreMembers(IMappableMember member)
+    public void IgnoreMembers(IMappableMember member) => IgnoreMembers(member.Name);
+
+    public void IgnoreMembers(string name)
     {
-        _unmappedSourceMemberNames.Remove(member.Name);
-        _unmappedTargetMemberNames.Remove(member.Name);
-        ignoredSourceMemberNames.Add(member.Name);
+        _unmappedSourceMemberNames.Remove(name);
+        _unmappedTargetMemberNames.Remove(name);
+        ignoredSourceMemberNames.Add(name);
 
-        if (!HasMemberConfig(member.Name))
+        if (!HasMemberConfig(name))
         {
-            targetMembers.Remove(member.Name);
+            targetMembers.Remove(name);
         }
     }
 

src/Riok.Mapperly/Descriptors/MappingBodyBuilders/EnumerableMappingBodyBuilder.cs

@@ -9,6 +9,7 @@ namespace Riok.Mapperly.Descriptors.MappingBodyBuilders;
 internal static class EnumerableMappingBodyBuilder
 {
     private const string SystemNamespaceName = "System";
+    private const string CapacityMemberName = "Capacity";
 
     private static readonly IReadOnlyCollection<string> _sourceCountAlias =
     [
@@ -35,13 +36,13 @@ public static void BuildMappingBody(MappingBuilderContext ctx, IEnumerableMappin
         // include the target count as the target could already include elements
         if (CapacitySetterBuilder.TryBuildCapacitySetter(ctx, mapping.CollectionInfos, true) is { } capacitySetter)
         {
-            if (capacitySetter.CapacityTargetMember != null)
-            {
-                mappingCtx.IgnoreMembers(capacitySetter.CapacityTargetMember);
-            }
-
+            mappingCtx.IgnoreMembers(CapacityMemberName);
             mapping.AddCapacitySetter(capacitySetter);
         }
+        else
+        {
+            IgnoreCapacityIfSystemType(mappingCtx);
+        }
 
         ObjectMemberMappingBodyBuilder.BuildMappingBody(mappingCtx);
         mappingCtx.AddDiagnostics();
@@ -72,6 +73,15 @@ private static void IgnoreSystemMembers<T>(IMembersBuilderContext<T> ctx, ITypeS
         }
     }
 
+    private static void IgnoreCapacityIfSystemType<T>(IMembersBuilderContext<T> ctx)
+        where T : IEnumerableMapping
+    {
+        if (ctx.Mapping.SourceType.IsInRootNamespace(SystemNamespaceName) || ctx.Mapping.TargetType.IsInRootNamespace(SystemNamespaceName))
+        {
+            ctx.IgnoreMembers(CapacityMemberName);
+        }
+    }
+
     private static void BuildConstructorMapping(INewInstanceBuilderContext<INewInstanceEnumerableMapping> ctx)
     {
         // allow source count being mapped to a target constructor parameter
@@ -108,12 +118,12 @@ private static void BuildConstructorMapping(INewInstanceBuilderContext<INewInsta
                 ctx.IgnoreMembers(ctx.Mapping.CollectionInfos.Source.CountMember);
             }
 
-            if (capacitySetter.CapacityTargetMember != null)
-            {
-                ctx.IgnoreMembers(capacitySetter.CapacityTargetMember);
-            }
-
+            ctx.IgnoreMembers(CapacityMemberName);
             ctx.Mapping.AddCapacitySetter(capacitySetter);
         }
+        else
+        {
+            IgnoreCapacityIfSystemType(ctx);
+        }
     }
 }

src/Riok.Mapperly/Helpers/SymbolExtensions.cs

@@ -238,11 +238,11 @@ internal static IEnumerable<ITypeSymbol> WalkTypeHierarchy(this ITypeSymbol symb
     internal static bool IsInRootNamespace(this ISymbol symbol, string ns)
     {
         var namespaceSymbol = symbol.ContainingNamespace;
-        while (namespaceSymbol.ContainingNamespace is { IsGlobalNamespace: false })
+        while (namespaceSymbol?.ContainingNamespace is { IsGlobalNamespace: false })
         {
             namespaceSymbol = namespaceSymbol.ContainingNamespace;
         }
 
-        return string.Equals(namespaceSymbol.Name, ns, StringComparison.Ordinal);
+        return namespaceSymbol != null && string.Equals(namespaceSymbol.Name, ns, StringComparison.Ordinal);
     }
 }

test/Riok.Mapperly.Tests/Mapping/EnumerableCustomTest.cs

@@ -381,4 +381,57 @@ public void CustomCollectionToCustomCollectionWithObjectFactory()
                 """
             );
     }
+
+    [Fact]
+    public void CustomCollectionToGetOnlyICollection()
+    {
+        var source = TestSourceBuilder.Mapping(
+            "A",
+            "B",
+            "class A { public C Value { get; } }",
+            "class B { public ICollection<int> Value { get; } }",
+            "class C : IEnumerable<int> { public int Capacity { get; } public int Count { get; } }"
+        );
+        TestHelper
+            .GenerateMapper(source, TestHelperOptions.AllowAndIncludeAllDiagnostics)
+            .Should()
+            .HaveAssertedAllDiagnostics()
+            .HaveSingleMethodBody(
+                """
+                var target = new global::B();
+                foreach (var item in source.Value)
+                {
+                    target.Value.Add(item);
+                }
+                return target;
+                """
+            );
+    }
+
+    [Fact]
+    public void CustomCollectionToGetOnlyList()
+    {
+        var source = TestSourceBuilder.Mapping(
+            "A",
+            "B",
+            "class A { public C Value { get; } }",
+            "class B { public List<int> Value { get; } }",
+            "class C : IEnumerable<int> { public int Capacity { get; } public int Count { get; } }"
+        );
+        TestHelper
+            .GenerateMapper(source, TestHelperOptions.AllowAndIncludeAllDiagnostics)
+            .Should()
+            .HaveAssertedAllDiagnostics()
+            .HaveSingleMethodBody(
+                """
+                var target = new global::B();
+                target.Value.EnsureCapacity(source.Value.Count + target.Value.Count);
+                foreach (var item in source.Value)
+                {
+                    target.Value.Add(item);
+                }
+                return target;
+                """
+            );
+    }
 }