chore: common linq loop allocations, add small optimisations

src/Riok.Mapperly/Descriptors/Enumerables/CollectionInfoBuilder.cs

@@ -21,7 +21,7 @@
             if (TypeFullName != null)
                 return types.TryGet(TypeFullName);
 
             throw new InvalidOperationException("One type needs to be set for each collection type");
         }
     }
 
@@ -100,7 +100,7 @@
             typeInfo,
             GetImplementedCollectionTypes(wellKnownTypes, type, typeInfo),
             enumeratedType,
-            FindCountProperty(wellKnownTypes, symbolAccessor, type, typeInfo),
+            FindCountProperty(symbolAccessor, type, typeInfo),
             HasValidAddMethod(wellKnownTypes, type, typeInfo),
             collectionTypeInfo?.Immutable == true
         );
@@ -115,18 +115,27 @@
         if (type is not ({ IsValueType: true, IsReadOnly: true } and INamedTypeSymbol { TypeArguments.Length: 1 } namedType))
             return null;
 
-        // if the collection is Span<> or Memory<> etc, get the type symbol
+        // if the collection is a ref type the check for Span<> or ReadOnlySpanSpan<>
         if (
-            SymbolEqualityComparer.Default.Equals(type.OriginalDefinition, types.Get(typeof(Span<>)))
-            || SymbolEqualityComparer.Default.Equals(type.OriginalDefinition, types.Get(typeof(ReadOnlySpan<>)))
-            || SymbolEqualityComparer.Default.Equals(type.OriginalDefinition, types.Get(typeof(Memory<>)))
+            namedType.IsRefLikeType
+            && (
+                SymbolEqualityComparer.Default.Equals(type.OriginalDefinition, types.Get(typeof(Span<>)))
+                || SymbolEqualityComparer.Default.Equals(type.OriginalDefinition, types.Get(typeof(ReadOnlySpan<>)))
+            )
+        )
+        {
+            return namedType.TypeArguments[0];
+        }
+        // Memory<> or ReadOnlyMemory<> etc, get the type symbol
+        if (
+            SymbolEqualityComparer.Default.Equals(type.OriginalDefinition, types.Get(typeof(Memory<>)))
             || SymbolEqualityComparer.Default.Equals(type.OriginalDefinition, types.Get(typeof(ReadOnlyMemory<>)))
         )
         {
             return namedType.TypeArguments[0];
         }
 
         return null;
     }
 
     private static bool HasValidAddMethod(WellKnownTypes types, ITypeSymbol t, CollectionType typeInfo)
@@ -149,7 +158,7 @@
             || t.HasImplicitGenericImplementation(types.Get(typeof(ISet<>)), nameof(ISet<object>.Add));
     }
 
-    private static string? FindCountProperty(WellKnownTypes types, SymbolAccessor symbolAccessor, ITypeSymbol t, CollectionType typeInfo)
+    private static string? FindCountProperty(SymbolAccessor symbolAccessor, ITypeSymbol t, CollectionType typeInfo)
     {
         if (typeInfo is CollectionType.IEnumerable)
             return null;
@@ -170,7 +179,7 @@
         var member = symbolAccessor
             .GetAllAccessibleMappableMembers(t)
             .FirstOrDefault(
-                x => x.Name is nameof(ICollection<object>.Count) or nameof(Array.Length) && x.Type.SpecialType == SpecialType.System_Int32
+                x => x.Type.SpecialType == SpecialType.System_Int32 && x.Name is nameof(ICollection<object>.Count) or nameof(Array.Length)
             );
         return member?.Name;
     }
@@ -187,7 +196,7 @@
         foreach (var typeInfo in _collectionTypeInfos)
         {
             if (typeInfo.GetTypeSymbol(types) is not { } typeSymbol)
                 continue;
 
             if (SymbolEqualityComparer.Default.Equals(type.OriginalDefinition, typeSymbol))
                 return typeInfo;
@@ -335,7 +344,7 @@
             foreach (var typeInfo in _collectionTypeInfos)
             {
                 if (typeInfo.GetTypeSymbol(types) is not { } typeSymbol)
                     continue;
 
                 if (type.ImplementsGeneric(typeSymbol, out _))
                 {

src/Riok.Mapperly/Descriptors/SymbolAccessor.cs

@@ -22,8 +22,13 @@
         where T : Attribute
     {
         var attributeSymbol = _types.Get<T>();
-        return GetAttributesCore(symbol)
-            .Where(x => SymbolEqualityComparer.Default.Equals(x.AttributeClass?.ConstructedFrom ?? x.AttributeClass, attributeSymbol));
+        foreach (var attr in GetAttributesCore(symbol))
+        {
+            if (SymbolEqualityComparer.Default.Equals(attr.AttributeClass?.ConstructedFrom ?? attr.AttributeClass, attributeSymbol))
+            {
+                yield return attr;
+            }
+        }
     }
 
     internal bool HasAttribute<T>(ISymbol symbol)
@@ -67,7 +72,13 @@
 
     internal IEnumerable<IMappableMember> GetMappableMembers(ITypeSymbol symbol, string name, IEqualityComparer<string> comparer)
     {
-        return GetAllAccessibleMappableMembers(symbol).Where(x => comparer.Equals(name, x.Name));
+        foreach (var member in GetAllAccessibleMappableMembers(symbol))
+        {
+            if (comparer.Equals(name, member.Name))
+            {
+                yield return member;
+            }
+        }
     }
 
     private IEnumerable<ISymbol> GetAllMembers(ITypeSymbol symbol, string name) => GetAllMembers(symbol).Where(x => name.Equals(x.Name));

src/Riok.Mapperly/Helpers/NullableSymbolExtensions.cs

@@ -5,8 +5,6 @@ namespace Riok.Mapperly.Helpers;
 
 public static class NullableSymbolExtensions
 {
-    private const string NullableGenericTypeName = "System.Nullable<T>";
-
     internal static bool HasSameOrStricterNullability(this ITypeSymbol symbol, ITypeSymbol other)
     {
         return symbol.NullableAnnotation == NullableAnnotation.NotAnnotated
@@ -109,10 +107,7 @@ internal static bool IsNullable(this ITypeParameterSymbol typeParameter, Nullabl
 
     private static ITypeSymbol? NonNullableValueType(this ITypeSymbol symbol)
     {
-        if (
-            symbol is INamedTypeSymbol { IsValueType: true, IsGenericType: true } namedType
-            && namedType.ConstructedFrom.ToDisplayString() == NullableGenericTypeName
-        )
+        if (symbol.IsValueType && symbol is INamedTypeSymbol { OriginalDefinition.SpecialType: SpecialType.System_Nullable_T } namedType)
             return namedType.TypeArguments[0];
         return null;
     }

src/Riok.Mapperly/Helpers/SymbolExtensions.cs

@@ -70,10 +70,17 @@ internal static bool ImplementsGeneric(
             return true;
         }
 
-        typedInterface = t.AllInterfaces.FirstOrDefault(
-            x => x.IsGenericType && SymbolEqualityComparer.Default.Equals(x.OriginalDefinition, genericInterfaceSymbol)
-        );
-        return typedInterface != null;
+        foreach (var typeSymbol in t.AllInterfaces)
+        {
+            if (typeSymbol.IsGenericType && SymbolEqualityComparer.Default.Equals(typeSymbol.OriginalDefinition, genericInterfaceSymbol))
+            {
+                typedInterface = typeSymbol;
+                return true;
+            }
+        }
+
+        typedInterface = null;
+        return false;
     }
 
     internal static bool ImplementsGeneric(