YAML LSP Schema Validation Error with Custom Tags (e.g., !include)

[peaceful-wanderer]

Describe the bug

The YAML Language Server shows a schema validation error when encountering custom tag !include. While the underlying parser correctly accepts the !include tag as valid YAML, the schema validator fails to interpret the tag's value. Instead of understanding that !include ./libs.yaml resolves to an object, the validator tries to validate the literal string ./libs.yaml against the schema's type definition, which expects a full object. This creates a false positive error that breaks validation

Expected Behavior

The validation error is a false positive,

Current Behavior

The schema validator does not process the custom tag. It sees the !include tag's value ./libs.yaml as the final value. It then tries to validate that this string against the schema's "type": "object" requirement, which fails.

Steps to Reproduce

1. Using the following schema :

{
  "type": "object",
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "properties": {
    "libs": {
      "type": "object",
      "description": "Library definitions",
      "additionalProperties": {
        "$ref": "#/$defs/library"
      }
    },
  }
}

2. Create main YAML file associated with the schema

libs: !include ./libs.yaml

3. The YAML LS will report an error similar to:
   Incorrect type. Expected "object". [YAML Schema]

Environment

• Windows
• Mac
• Linux
• other (please specify)
• Extension version : 1.18.0
• Vscode version : 1.103.2

[datho7561]

Did you configure the custom tag in the settings? https://github.com/redhat-developer/vscode-yaml?tab=readme-ov-file#adding-custom-tags

[datho7561]

It seems like the custom tag setting is not discoverable, perhaps we can provide a hint about it in the diagnostic or maybe provide a code action to register the custom tag as the expected type.