JSON schema does not allow strings on top-level

[cbratschi]

Describe the Bug

The following code always parses strings as JSON without checking the schema:

payload/packages/payload/src/fields/hooks/beforeChange/promise.ts

Line 139 in afcc970

JSON.parse(siblingData[field.name] as string)

If the following schema is being used, the JSON.parse() call fails but the value is valid:

                                        jsonSchema: {
                                            uri: 'a://b/foo.json', //dummy
                                            fileMatch: [ 'a://b/foo.json' ], //dummy

                                            schema: {
                                                        anyOf: [{
                                                            type: 'string'
                                                        }, {
                                                            type: 'number'
                                                        }, {
                                                            type: 'boolean'
                                                        }]
                                                    }
                                            }

Best solution is to check if the string value passes the schema before checking jsonError:

payload/packages/payload/src/fields/validations.ts

Line 344 in 6b051bd

return t('validation:invalidInput')

Link to the code that reproduces this issue

https://github.com/cbratschi/payload

Reproduction Steps

Binaries:
Node: 22.12.0
npm: 10.9.0
Yarn: 1.22.22
pnpm: N/A
Relevant Packages:
payload: 3.13.0
Operating System:
Platform: darwin
Arch: arm64
Version: Darwin Kernel Version 24.1.0: Thu Oct 10 21:05:23 PDT 2024; root:xnu-11215.41.3~2/RELEASE_ARM64_T6031
Available memory (MB): 65536
Available CPU cores: 16

Which area(s) are affected? (Select all that apply)

area: core

Environment Info

See above.

[cbratschi]

Workaround was:

                                    //data (JSON)
                                    <JSONField>{
                                        name: 'data',
                                        type: 'json',

                                        jsonSchema: {
                                            uri: 'a://b/foo.json', //dummy
                                            fileMatch: [ 'a://b/foo.json' ], //dummy

                                            schema: {
                                                //see https://ajv.js.org/strict-mode.html#strict-types
                                                //Note: cannot use a string here, have to use an object (see https://github.com/payloadcms/payload/blob/afcc970e3609c1bb6f2d59c4cbbb36ac62730ec9/packages/payload/src/fields/hooks/beforeChange/promise.ts#L137)
                                                //see https://github.com/payloadcms/payload/issues/10542

                                                //Note: we better use an object here, can still add more values in future
                                                type: 'object',

                                                properties: {
                                                    value: {
                                                        anyOf: [{
                                                            type: 'string'
                                                        }, {
                                                            type: 'number'
                                                        }, {
                                                            type: 'boolean'
                                                        }]
                                                    }
                                                },

                                                additionalProperties: false
                                            }
                                        },

                                    required: false
                                },