Changing default value on another property value

Summary

I have the following schema (it is just a simplified jekyll.json from my PR):

{
  "$schema": "http://json-schema.org/draft-07/schema",
  "$comment": "https://jekyllrb.com/docs/configuration/",
  "title": "Jekyll static site generator config file schema",
  "definitions": {
    "implementation": {
      "description": "The implementation to use",
      "type": "string",
      "enum": [
        "sassc",
        "sass-embedded"
      ],
      "default": "sassc"
    }
  },
  "type": "object",
  "properties": {
    "sass": {
      "description": "Sass options",
      "type": "object",
      "properties": {
        "implementation": {
          "$ref": "#/definitions/implementation"
        }
      },
      "allOf": [
        {
          "if": {
            "properties": {
              "implementation": {
                "const": "sassc"
              }
            }
          },
          "then": {
            "type": "object",
            "properties": {
              "implementation": {
                "$ref": "#/definitions/implementation"
              },
              "style": {
                "description": "Style of CSS-output",
                "type": "string",
                "enum": [
                  "nested",
                  "compact",
                  "compressed",
                  "expanded"
                ],
                "default": "compact"
              }
            },
            "additionalProperties": true
          },
          "else": {
            "type": "object",
            "properties": {
              "implementation": {
                "$ref": "#/definitions/implementation"
              },
              "style": {
                "description": "Style of CSS-output",
                "type": "string",
                "enum": [
                  "nested",
                  "compact",
                  "compressed",
                  "expanded"
                ],
                "default": "expanded"
              }
            },
            "additionalProperties": false
          }
        }
      ],
      "additionalProperties": false
    }
  },
  "additionalProperties": false
}

Default style value must be dependant on implementation value:

• if implementation is sassc then style default is compact
• else style default is expanded

The problem is that when I try to use my style property I obtain: Property style is not allowed. error:

How to fix this problem?

Relevant information

No repository file or test is named. Reproduce the reported style error with the simplified schema, then trace the YAML language server's handling of conditional allOf schemas and property completion. Done means the conditional schema no longer reports style as disallowed and applies the expected default for each implementation.