Add `InferEnum` type

[totigm]

Add a generic utility type InferEnum to facilitate type inference for enums defined with pgEnum. This enhancement aligns with the existing InferSelectModel and InferInsertModel utilities, simplifying type definitions for enums in Drizzle ORM.

Proposed Changes

Addition of the InferEnum type: A generic type that infers the possible values of an enum defined with pgEnum. This does not affect the existing functionality of the ORM. It merely adds a new utility type that developers can choose to use.

export type InferEnum<T> = T extends { enumValues: readonly (infer U)[] }
  ? U
  : never;

Usage

Example before the change:

const status = pgEnum("status", ["pending", "completed", "cancelled"]);
type Status = (typeof status.enumValues)[number];

Example after the change:

const status = pgEnum("status", ["pending", "completed", "cancelled"]);
type Status = InferEnum<typeof status>;

Benefits

• Simplifies and improves code readability when defining enum types.
• Provides a consistent and intuitive API.