feat: add typescript.postProcess hook for type generation

[JarrodMFlesch]

Summary

This pr would allow us to import a generic from the plugin and then use it. The limitation with json-schema-to-typescript is the inability to generate a type in the file that takes generics.

There are some generated generics plopped in, internally by our addSelectGenericsToGeneratedTypes function.

This PR exposes a way for external plugins to manipulate the generated config post-processing of json-schema-to-typescript which is not possible today.

Implementation

In packages/payload/src/bin/generateTypes.ts, after addSelectGenericsToGeneratedTypes:

if (config.typescript?.postProcess?.length) {
  for (const fn of config.typescript.postProcess) {
    compiled = fn(compiled);
  }
}

Add to TypeScript config type:

typescript?: {
  postProcess?: Array<(compiled: string) => string>;
}

Use cases

• Inject imports from plugin packages
• Add utility types

Example

// Plugin adds an import and uses it via tsType on fields

typescript: {
  postProcess: [
    ...(config.typescript?.postProcess || []),
    (compiled) => {
      const importStmt = `import type { MyPluginType } from '@payloadcms/my-plugin';`;
      return compiled.replace(/(\/\*[\s\S]*?\*\/\n)/, `$1\n${importStmt}\n`);
    },
  ],
}

Notes

• Follows existing pattern (Payload already post-processes for Select generics)

[github-actions]

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