diff --git a/cli/compose/loader/loader.go b/cli/compose/loader/loader.go
index 2ddc858eab..28573dc4d5 100644
--- a/cli/compose/loader/loader.go
+++ b/cli/compose/loader/loader.go
@@ -297,10 +297,13 @@ func Transform(source interface{}, target interface{}, additionalTransformers ..
 	return decoder.Decode(source)
 }
 
+// TransformerFunc defines a function to perform the actual transformation
+type TransformerFunc func(interface{}) (interface{}, error)
+
 // Transformer defines a map to type transformer
 type Transformer struct {
 	TypeOf reflect.Type
-	Func   func(interface{}) (interface{}, error)
+	Func   TransformerFunc
 }
 
 func createTransformHook(additionalTransformers ...Transformer) mapstructure.DecodeHookFuncType {
@@ -684,7 +687,7 @@ func absPath(workingDir string, filePath string) string {
 	return filepath.Join(workingDir, filePath)
 }
 
-func transformMapStringString(data interface{}) (interface{}, error) {
+var transformMapStringString TransformerFunc = func(data interface{}) (interface{}, error) {
 	switch value := data.(type) {
 	case map[string]interface{}:
 		return toMapStringString(value, false), nil
@@ -695,7 +698,7 @@ func transformMapStringString(data interface{}) (interface{}, error) {
 	}
 }
 
-func transformExternal(data interface{}) (interface{}, error) {
+var transformExternal TransformerFunc = func(data interface{}) (interface{}, error) {
 	switch value := data.(type) {
 	case bool:
 		return map[string]interface{}{"external": value}, nil
@@ -706,7 +709,7 @@ func transformExternal(data interface{}) (interface{}, error) {
 	}
 }
 
-func transformServicePort(data interface{}) (interface{}, error) {
+var transformServicePort TransformerFunc = func(data interface{}) (interface{}, error) {
 	switch entries := data.(type) {
 	case []interface{}:
 		// We process the list instead of individual items here.
@@ -739,7 +742,7 @@ func transformServicePort(data interface{}) (interface{}, error) {
 	}
 }
 
-func transformStringSourceMap(data interface{}) (interface{}, error) {
+var transformStringSourceMap TransformerFunc = func(data interface{}) (interface{}, error) {
 	switch value := data.(type) {
 	case string:
 		return map[string]interface{}{"source": value}, nil
@@ -750,7 +753,7 @@ func transformStringSourceMap(data interface{}) (interface{}, error) {
 	}
 }
 
-func transformBuildConfig(data interface{}) (interface{}, error) {
+var transformBuildConfig TransformerFunc = func(data interface{}) (interface{}, error) {
 	switch value := data.(type) {
 	case string:
 		return map[string]interface{}{"context": value}, nil
@@ -761,7 +764,7 @@ func transformBuildConfig(data interface{}) (interface{}, error) {
 	}
 }
 
-func transformServiceVolumeConfig(data interface{}) (interface{}, error) {
+var transformServiceVolumeConfig TransformerFunc = func(data interface{}) (interface{}, error) {
 	switch value := data.(type) {
 	case string:
 		return ParseVolume(value)
@@ -772,8 +775,7 @@ func transformServiceVolumeConfig(data interface{}) (interface{}, error) {
 	}
 }
 
-// nolint: unparam
-func transformServiceNetworkMap(value interface{}) (interface{}, error) {
+var transformServiceNetworkMap TransformerFunc = func(value interface{}) (interface{}, error) {
 	if list, ok := value.([]interface{}); ok {
 		mapValue := map[interface{}]interface{}{}
 		for _, name := range list {
@@ -784,8 +786,7 @@ func transformServiceNetworkMap(value interface{}) (interface{}, error) {
 	return value, nil
 }
 
-// nolint: unparam
-func transformStringOrNumberList(value interface{}) (interface{}, error) {
+var transformStringOrNumberList TransformerFunc = func(value interface{}) (interface{}, error) {
 	list := value.([]interface{})
 	result := make([]string, len(list))
 	for i, item := range list {
@@ -794,7 +795,7 @@ func transformStringOrNumberList(value interface{}) (interface{}, error) {
 	return result, nil
 }
 
-func transformStringList(data interface{}) (interface{}, error) {
+var transformStringList TransformerFunc = func(data interface{}) (interface{}, error) {
 	switch value := data.(type) {
 	case string:
 		return []string{value}, nil
@@ -805,13 +806,13 @@ func transformStringList(data interface{}) (interface{}, error) {
 	}
 }
 
-func transformMappingOrListFunc(sep string, allowNil bool) func(interface{}) (interface{}, error) {
+func transformMappingOrListFunc(sep string, allowNil bool) TransformerFunc {
 	return func(data interface{}) (interface{}, error) {
 		return transformMappingOrList(data, sep, allowNil), nil
 	}
 }
 
-func transformListOrMappingFunc(sep string, allowNil bool) func(interface{}) (interface{}, error) {
+func transformListOrMappingFunc(sep string, allowNil bool) TransformerFunc {
 	return func(data interface{}) (interface{}, error) {
 		return transformListOrMapping(data, sep, allowNil), nil
 	}
@@ -850,14 +851,14 @@ func transformMappingOrList(mappingOrList interface{}, sep string, allowNil bool
 	panic(errors.Errorf("expected a map or a list, got %T: %#v", mappingOrList, mappingOrList))
 }
 
-func transformShellCommand(value interface{}) (interface{}, error) {
+var transformShellCommand TransformerFunc = func(value interface{}) (interface{}, error) {
 	if str, ok := value.(string); ok {
 		return shellwords.Parse(str)
 	}
 	return value, nil
 }
 
-func transformHealthCheckTest(data interface{}) (interface{}, error) {
+var transformHealthCheckTest TransformerFunc = func(data interface{}) (interface{}, error) {
 	switch value := data.(type) {
 	case string:
 		return append([]string{"CMD-SHELL"}, value), nil
@@ -868,7 +869,7 @@ func transformHealthCheckTest(data interface{}) (interface{}, error) {
 	}
 }
 
-func transformSize(value interface{}) (interface{}, error) {
+var transformSize TransformerFunc = func(value interface{}) (interface{}, error) {
 	switch value := value.(type) {
 	case int:
 		return int64(value), nil
@@ -878,7 +879,7 @@ func transformSize(value interface{}) (interface{}, error) {
 	panic(errors.Errorf("invalid type for size %T", value))
 }
 
-func transformStringToDuration(value interface{}) (interface{}, error) {
+var transformStringToDuration TransformerFunc = func(value interface{}) (interface{}, error) {
 	switch value := value.(type) {
 	case string:
 		d, err := time.ParseDuration(value)