Prototype: FieldDirective - auto-wrap resolvers with directive functions

[captbaritone]

Summary

• Adds a new FieldDirective type exported from grats that directive functions can return to opt into automatic resolver wrapping
• When a @gqlDirective function returns FieldDirective, Grats composes the directive wrapper around the field resolver in the generated schema
• Eliminates the need for manual mapSchema + getDirective wiring for the common case of field-level directive behavior

Example

import { Int, FieldDirective } from "grats";

/** @gqlDirective on FIELD_DEFINITION */
export function rateLimit(args: { max: Int }): FieldDirective {
  return (next) => (source, args, context, info) => {
    checkRateLimit(context, args.max);
    return next(source, args, context, info);
  };
}

Generated output

resolve: rateLimit({ max: 10 })(function resolve(source) {
    return queryLikesResolver(source);
})

Design decisions

• Opt-in via return type: Only directives that return FieldDirective get this behavior. Existing directives with void return type continue to work as metadata-only.
• Syntactic detection: FieldDirective is detected by name in the return type annotation (the extractor is purely syntactic, no type checker).
• Composable: Multiple FieldDirective directives on a single field nest naturally (outermost directive listed first).
• Follows existing patterns: Similar to how @semanticNonNull already wraps resolvers at codegen time.

Related

• Closes the common case discussed in Idea for discussion: Directive implementations #180
• Supersedes the approach sketched in Sketch an idea of what Grats could do for schema directives #182

Test plan

• New test fixture fieldDirectiveWrapper.ts validates the generated output
• Full test suite passes
• Manual testing with the production-app example

🤖 Generated with Claude Code

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