Preserve null collections in effective YAML

internal/config/effective_pipeline.go

@@ -1,9 +1,11 @@
 package config
 
 import (
+	"encoding/json"
 	"fmt"
 	"path/filepath"
 	"sort"
+	"strconv"
 	"strings"
 
 	"gopkg.in/yaml.v3"
@@ -151,13 +153,72 @@ func MarshalEffectivePipeline(cfg *PipelineConfig) ([]byte, error) {
 		return nil, fmt.Errorf("pipeline config is required")
 	}
 
-	data, err := yaml.Marshal(projectEffectivePipeline(cfg, true))
+	value, err := projectionValueTree(projectEffectivePipeline(cfg, true))
+	if err != nil {
+		return nil, err
+	}
+	node, err := effectiveYAMLNode(value)
+	if err != nil {
+		return nil, fmt.Errorf("serialize effective pipeline: %w", err)
+	}
+	data, err := yaml.Marshal(node)
 	if err != nil {
 		return nil, fmt.Errorf("serialize effective pipeline: %w", err)
 	}
 	return data, nil
 }
 
+func effectiveYAMLNode(value any) (*yaml.Node, error) {
+	switch value := value.(type) {
+	case nil:
+		return &yaml.Node{Kind: yaml.ScalarNode, Tag: "!!null", Value: "null"}, nil
+	case bool:
+		return &yaml.Node{Kind: yaml.ScalarNode, Tag: "!!bool", Value: strconv.FormatBool(value)}, nil
+	case string:
+		return &yaml.Node{Kind: yaml.ScalarNode, Tag: "!!str", Value: value}, nil
+	case json.Number:
+		tag := "!!int"
+		if strings.ContainsAny(value.String(), ".eE") {
+			tag = "!!float"
+		}
+		return &yaml.Node{Kind: yaml.ScalarNode, Tag: tag, Value: value.String()}, nil
+	case []any:
+		node := &yaml.Node{Kind: yaml.SequenceNode, Tag: "!!seq"}
+		if len(value) == 0 {
+			node.Style = yaml.FlowStyle
+		}
+		for _, item := range value {
+			child, err := effectiveYAMLNode(item)
+			if err != nil {
+				return nil, err
+			}
+			node.Content = append(node.Content, child)
+		}
+		return node, nil
+	case map[string]any:
+		node := &yaml.Node{Kind: yaml.MappingNode, Tag: "!!map"}
+		if len(value) == 0 {
+			node.Style = yaml.FlowStyle
+		}
+		keys := make([]string, 0, len(value))
+		for key := range value {
+			keys = append(keys, key)
+		}
+		sort.Strings(keys)
+		for _, key := range keys {
+			child, err := effectiveYAMLNode(value[key])
+			if err != nil {
+				return nil, err
+			}
+			node.Content = append(node.Content,
+				&yaml.Node{Kind: yaml.ScalarNode, Tag: "!!str", Value: key}, child)
+		}
+		return node, nil
+	default:
+		return nil, fmt.Errorf("unsupported projected value type %T", value)
+	}
+}
+
 func effectivePipelineOwners(cfg *PipelineConfig) map[string][]string {
 	owners := make(map[string][]string)
 	if cfg == nil || cfg.resolution == nil {