way to define an object type from its interface guard

[turadg]

What is the Problem Being Solved?

Consider,

/**
 * @typedef {object} App
 * @property {(obj: any) => Promise<unknown>} upcall return value depends on the
 *   bridge semantics
 */
export const AppI = M.interface('App', {
  upcall: M.call(M.any()).returns(M.promise()),
});

// contrived
/** @typedef {(target: string, app: ERef<App>) => Promise<TargetUnregister>} registerApp */

The guards define the interface, but:

1. lose some useful type data
2. define a guard object versus a usable one

So a type has to be specified for App, but AppI doesn't get an annotation so:

1. the typedef appears to be an annotation when it isn't
2. the names are repeated

Description of the Design

#6160 is to solve this generally but a stop-gap could be:

/**
 * @typedef {object} App
 * @property {(obj: any) => Promise<unknown>} upcall return value depends on the
 *   bridge semantics
 */
/** @type {GuardInterface<App>} */
export const AppI = M.interface('App', {
  upcall: M.call(M.any()).returns(M.promise()),
});

See also,

• feat: checked cast with TypedMatcher #8394
• typecheck for arity in Exo guards #8709

Security Considerations

Scaling Considerations

Test Plan

Upgrade Considerations