An attempt at developing a type that can infer the correct keys/value types for an interface based on a given schema.

kipper-scheme-typing.ts

/**
 * The validation scheme for an option that is an object.
 * @since 0.11.0
 */
export type KipperConfigObjectValidatorScheme = {
	[key: string]: "string" | "boolean" | "array<string>" | KipperConfigObjectValidatorScheme;
}

/**
 * The validation scheme for the Kipper config.
 *
 * Note that while no undefined types are specified, not all options have to be specified. This depends on the
 * implementation of the {@link ConfigInterpreter}, but not defined arguments will usually be assigned a default value (
 * like with the implementation of the default {@link ConfigInterpreter}, with the exception )
 * @since 0.11.0
 */
export type KipperBaseConfigScheme = KipperConfigObjectValidatorScheme & {
	/**
	 * The only option that is always allowed in the config is the `extends` option, which is used to extend another
	 * config. May be a relative or absolute path.
	 * @since 0.11.0
	 */
	"extends": "string";
};

/**
 * The default scheme for a Kipper config file, which is used to validate the config.
 *
 * This scheme is the default scheme used by the {@link ConfigInterpreter} class, which will per default also only
 * understand this scheme.
 * @since 0.11.0
 */
export const defaultKipperConfigScheme = {
	"extends": "string",
	"version": "string",
	"compileConfig": {
		"target": "string",
		"warnings": "boolean",
		"recover": "boolean",
		"optimisationOptions": {
			"optimiseInternals": "boolean",
			"optimiseBuiltIns": "boolean",
		},
	},
	"resources": "array<string>",
} satisfies KipperConfigObjectValidatorScheme & KipperBaseConfigScheme;

/**
 * The type of the default scheme for a Kipper config file.
 *
 * This scheme is the default scheme used by the {@link ConfigInterpreter} class, which will per default also only
 * understand this scheme.
 * @since 0.11.0
 */
export type DefaultKipperConfigScheme = typeof defaultKipperConfigScheme;

/**
 * The default Kipper config output format.
 *
 * This will be generated when the {@link defaultKipperConfigScheme} is passed to the default {@link ConfigInterpreter}
 * class.
 * @since 0.11.0
 */
export type DefaultKipperConfigOutput = {
	"compileConfig": CompileConfig,
} & Partial<{
	"version": string,
	"resources": Array<path.ParsedPath>,
}>

/**
 * The config type of the given scheme type.
 *
 * This type is used to generate the config type from the given scheme type, which represents the object type which the
 * config has to follow.
 * @since 0.11.0
 */
export type KipperConfig<T extends KipperConfigObjectValidatorScheme> = NonNullable<{
	[K in keyof T as T[K] extends "string" | "boolean" | "array<string>" | KipperConfigObjectValidatorScheme ? K : never]?:
		T[K] extends "string" ? string :
		T[K] extends "boolean" ? boolean :
		T[K] extends "array<string>" ? Array<string> :
		T[K] extends KipperConfigObjectValidatorScheme ? KipperConfig<T[K]> :
		never;
}>;

var x: KipperConfig<typeof defaultKipperConfigScheme> = {
	"extends": "string",
};
x.compileConfig!!.warnings = true;