"allOf" Support for the custom JSON schema keywords merging

[Dzuming]

Prerequisites

• I have read the documentation

What theme are you using?

core

Is your feature request related to a problem? Please describe.

In a JSON schema, there is a possibility to use if else then. I want to define a JSON schema with a custom keyword

...
        "properties": {
          "hasDescription": {
            "type": "boolean"

          },
          "description": {
            "type": "string",
            "customProperty": {
              "isImportant": false
            }
          },
        }
...

"allOf": [
          {
            "if": {
              "properties": {
                "hasDescription": {
                  "const": true
                }
              }
            },
            "then": {
              "properties": {
                "description": {
                  "customProperty": {
                    "isImportant": true
                  }
                }
              }
            },
            "else": {}
          }
        ]

If all of the conditions are met in the form, there is a warning in the console, and values are not merged:

could not merge subschemas in allOf:
Error: No resolver found for key customProperty. You can provide a resolver for this keyword in the options, or provide a default resolver

Describe the solution you'd like

RJSF library uses json schema merge all library under the hood to merge subschemas. There is an option to add custom resolvers via options property .

Now, packages/utils/src/schema/retrieveSchema.ts code where merging happens looks like

 if (ALL_OF_KEY in schema) {
    try {
      resolvedSchema = mergeAllOf({
        ...resolvedSchema,
        allOf: resolvedSchema.allOf,
      }) as S;
    } catch (e) {
      console.warn("could not merge subschemas in allOf:\n" + e);
      const { allOf, ...resolvedSchemaWithoutAllOf } = resolvedSchema;
      return resolvedSchemaWithoutAllOf as S;
    }
  }

The idea is to be able to provide custom mergeAllOf resolvers

resolvedSchema = mergeAllOf({
        ...resolvedSchema,
        allOf: resolvedSchema.allOf,
      }, 
      {
          resolvers: customResolvers
) as S;

So the end result will be like

resolvedSchema = mergeAllOf({
        ...resolvedSchema,
        allOf: resolvedSchema.allOf,
      }, 
      {
          resolvers: {
            customProperty: function (values, path, mergeSchemas, options) {
              return { ...values[0], ...values[1] };
            },
          },
        }
) as S;

Describe alternatives you've considered

No response

[heath-freenome]

@Dzuming are you willing to work with us to build this new feature? We are a small team with barely any time to fix bugs