🐛 Fix corruption when map or seq templating changes the style

internal/node/has_comment.go

@@ -61,3 +61,28 @@ func GetCommentTmpl(prefix string, n *yaml.Node) (string, TmplTag) {
 	}
 	return "", DynamicTag
 }
+
+// MoveComment moves a comment between yaml.Node entries after a style change.
+// When a yaml.MappingNode or yaml.SequenceNode has an inline comment,
+// the decoder will set LineComment differently according to the node's style.
+//
+// When value(s) are on a single line (flow style), LineComment will be set on the value.
+// When value(s) are on multiple lines (block style), LineComment will be set on the key.
+//
+// If templating changes the node's style, the comment needs to move or else
+// encoding errors will occur.
+func MoveComment(key, val *yaml.Node) {
+	if val.Kind != yaml.SequenceNode && val.Kind != yaml.MappingNode {
+		return
+	}
+
+	if len(val.Content) > 0 && val.LineComment != "" && key.LineComment == "" {
+		// Flow to block style: move comment from value to key.
+		key.LineComment = val.LineComment
+		val.LineComment = ""
+	} else if len(val.Content) == 0 && key.LineComment != "" && val.LineComment == "" {
+		// Block to flow style: move comment from key to value.
+		val.LineComment = key.LineComment
+		key.LineComment = ""
+	}
+}

internal/visitor/template_comments.go

@@ -53,14 +53,17 @@ func (t TemplateComments) Run(n *yaml.Node) error {
 					}
 				} else {
 					// Current node was templated, do not need to traverse children
+					node.MoveComment(key, val)
 					continue
 				}
 			}
 
-			// Key did not have comment, run again with value.
+			// Key did not have comment, traversing children.
 			if err := t.Run(val); err != nil {
 				return err
 			}
+
+			node.MoveComment(key, val)
 		}
 	default:
 		for _, n := range n.Content {