fix: typescript schema to allow nullable fields

[johannesjo]

Otherwise any schema with a type like:

   myfield: {
      type: ["string", "null"],
    },

will produce an error.

This PR contains:

Describe the problem you have without this PR

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• Tests
• Documentation
• Typings
• Changelog

[pubkey]

I am sorry but this is wrong at many points.(string & {}) is allowed which is not reflected in your array. Also there can be more then 2 types which is not reflected by that change.

Also there is no test. Below the codes states type?: JsonSchemaTypes | JsonSchemaTypes[]; so what your are trying to do should work already.

Notice that it is recommended to use undefined for optional fields, not a mixed type with null. By default all fields in json-schema are optional.

[johannesjo]

Sorry for the wrong code.

Here is the minimal case to reproduce the underlying problem:

export const TEST_SCHEMA_LITERAL = {
  title: "test",
  version: 0,
  primaryKey: "id",
  type: "object",
  properties: {
    id: {
      type: "string",
    },
    completion_date: {
      type: ["string", "null"],
    },
  },
  required: [
    "id",
  ],
  indexes: [],
} as const;

const SCHEMA_TYPED = toTypedRxJsonSchema(TEST_SCHEMA_LITERAL);
export type RxSubtaskDocumentType = ExtractDocumentTypeFromTypedRxJsonSchema<
  typeof SCHEMA_TYPED
>;

export const TEST_SCHEMA: RxJsonSchema<RxSubtaskDocumentType> = TEST_SCHEMA_LITERAL;
//  => Throws TS Error

Which throws the error  The type 'readonly ["string", "null"]' is 'readonly' and cannot be assigned to the mutable type 'JsonSchemaTypes[]':

TS2322: Type '{ readonly title: "test"; readonly version: 0; readonly primaryKey: "id"; readonly type: "object"; readonly properties: { readonly id: { readonly type: "string"; }; readonly completion_date: { readonly type: readonly ["string", "null"]; }; }; readonly required: readonly [...]; readonly indexes: readonly []; }' is not assignable to type 'RxJsonSchema<{ id: string; completion_date?: string | null | undefined; }>'.   The types of 'properties.completion_date.type' are incompatible between these types.     Type 'readonly ["string", "null"]' is not assignable to type 'JsonSchemaTypes | JsonSchemaTypes[] | undefined'.       The type 'readonly ["string", "null"]' is 'readonly' and cannot be assigned to the mutable type 'JsonSchemaTypes[]'

A possible workaround is casting the type:

["string", "null"] as JsonSchemaTypes[]
// or
["string", "null"] as string[]

[pubkey]

Looks good now. Merged!