fix: Ignore custom functions for directly assignable types

Author: dranikpg

README.md

@@ -107,7 +107,7 @@ mapper.Map(&to, from)
 
 ##### Conversion functions
 
-They are used to convert one type into another. Conversion functions have the highest priority. The second argument is the current mapper instance and is optional.
+They are used to convert one type into another and have the highest priority, however they are not applied to fields of directly assignable structs. The second argument is the current mapper instance and is optional.
 
 ```go
 mapper.AddConvFunc(func(p RawPassword, mapper *Mapper) PasswordHash {
@@ -117,7 +117,7 @@ mapper.AddConvFunc(func(p RawPassword, mapper *Mapper) PasswordHash {
 
 ##### Inspection functions 
 
-Those are triggered _after_ a value has been successfully mapped. The value is **always taken by pointer**.
+Those are triggered _after_ a value has been successfully mapped. The value is **always taken by pointer**. Likewise to conversion functions, they are not called for fields of directly assignable structs.
 
 ```go
 mapper.AddInspectFunc(func(dto *UserDto) {

dto.go

@@ -93,16 +93,6 @@ func errorFromReflectValue(rv reflect.Value) error {
 	return err
 }
 
-// isCompositeKind returns true if this type contains other types (is composite)
-func isCompositeKind(k reflect.Kind) bool {
-	switch k {
-	case reflect.Struct, reflect.Slice, reflect.Map:
-		return true
-	default:
-		return false
-	}
-}
-
 // ==================================== Conversion and inspection functions ===
 
 // Run inspect functions for (dst-src) pair
@@ -366,19 +356,16 @@ func (m *Mapper) mapValue(dstRv, srcRv reflect.Value) (returnError error) {
 		return err
 	}
 
-	// don't skip calling functions for assignable types
-	if !m.HasCustomFuncs() || !isCompositeKind(fk) {
-		// 2. Check direct assignment
-		if srcRv.Type().AssignableTo(dstRv.Type()) {
-			dstRv.Set(srcRv)
-			return
-		}
+	// 2. Check direct assignment
+	if srcRv.Type().AssignableTo(dstRv.Type()) {
+		dstRv.Set(srcRv)
+		return
+	}
 
-		// 3. Check conversion
-		if srcRv.Type().ConvertibleTo(dstRv.Type()) {
-			dstRv.Set(srcRv.Convert(dstRv.Type()))
-			return
-		}
+	// 3. Check conversion
+	if srcRv.Type().ConvertibleTo(dstRv.Type()) {
+		dstRv.Set(srcRv.Convert(dstRv.Type()))
+		return
 	}
 
 	// 4. Handle pointers by dereferencing from

dto_test.go

@@ -306,21 +306,6 @@ func TestErrorPropagation(t *testing.T) {
 	assert.Equal(t, testError, err)
 }
 
-// Test custom functions are not skipped for assignable types
-func TestDontSkipFunctions(t *testing.T) {
-	var outProduct Product
-	testProduct := commonProducts[0]
-
-	testError := errors.New("Called!")
-
-	m := Mapper{}
-	m.AddConvFunc(func(s string) (string, error) {
-		return "", testError
-	})
-	err := m.Map(&outProduct, testProduct)
-	assert.Equal(t, testError, err)
-}
-
 func TestPointerCases(t *testing.T) {
 	{
 		var fromProduct = struct {