feat: add extensible transform API for custom field transformations

Signed-off-by: Evgenii Orlov <[email protected]>

Author: OrlovEvgeny

transform/canonical.go

@@ -20,7 +20,11 @@ import (
 	"github.com/compose-spec/compose-go/v2/tree"
 )
 
-type transformFunc func(data any, p tree.Path, ignoreParseError bool) (any, error)
+// TransformFunc is a function that can transform data at a specific path
+type TransformFunc func(data any, p tree.Path, ignoreParseError bool) (any, error)
+
+// For backward compatibility
+type transformFunc = TransformFunc
 
 var transformers = map[tree.Path]transformFunc{}
 

transform/defaults.go

@@ -20,16 +20,23 @@ import (
 	"github.com/compose-spec/compose-go/v2/tree"
 )
 
-var defaultValues = map[tree.Path]transformFunc{}
+// DefaultValues contains the default value transformers for compose fields
+var DefaultValues = map[tree.Path]TransformFunc{}
 
 func init() {
-	defaultValues["services.*.build"] = defaultBuildContext
-	defaultValues["services.*.secrets.*"] = defaultSecretMount
-	defaultValues["services.*.ports.*"] = portDefaults
-	defaultValues["services.*.deploy.resources.reservations.devices.*"] = deviceRequestDefaults
-	defaultValues["services.*.gpus.*"] = deviceRequestDefaults
+	DefaultValues["services.*.build"] = defaultBuildContext
+	DefaultValues["services.*.secrets.*"] = defaultSecretMount
+	DefaultValues["services.*.ports.*"] = portDefaults
+	DefaultValues["services.*.deploy.resources.reservations.devices.*"] = deviceRequestDefaults
+	DefaultValues["services.*.gpus.*"] = deviceRequestDefaults
 }
 
+// RegisterDefaultValue registers a custom transformer for the given path pattern
+func RegisterDefaultValue(path string, transformer TransformFunc) {
+	DefaultValues[tree.Path(path)] = transformer
+}
+
+
 // SetDefaultValues transforms a compose model to set default values to missing attributes
 func SetDefaultValues(yaml map[string]any) (map[string]any, error) {
 	result, err := setDefaults(yaml, tree.NewPath())
@@ -40,7 +47,7 @@ func SetDefaultValues(yaml map[string]any) (map[string]any, error) {
 }
 
 func setDefaults(data any, p tree.Path) (any, error) {
-	for pattern, transformer := range defaultValues {
+	for pattern, transformer := range DefaultValues {
 		if p.Matches(pattern) {
 			t, err := transformer(data, p, false)
 			if err != nil {

transform/ports.go

@@ -18,7 +18,7 @@ package transform
 
 import (
 	"fmt"
-
+	
 	"github.com/compose-spec/compose-go/v2/tree"
 	"github.com/compose-spec/compose-go/v2/types"
 	"github.com/go-viper/mapstructure/v2"