schemaErrorFormatter uses an insufficient validation type

[zedeus]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Fastify version

4.2.0

Plugin version

No response

Node.js version

16.15.1

Operating system

Linux

Operating system version (i.e. 20.04, 11.3, 10)

Irrelevant

Description

The FastifySchemaValidationError type used for the schemaErrorFormatter callback has a small subset of the fields available from the full Ajv validation error object.

fastify/types/schema.d.ts

Lines 25 to 28 in 8fccc46

	export interface FastifySchemaValidationError {
	message?: string;
	instancePath: string;
	}

This is the proper object:

fastify/fastify.d.ts

Lines 178 to 190 in 8fccc46

	declare module '@fastify/error' {
	interface FastifyError {
	validation?: ValidationResult[];
	}
	}
	export interface ValidationResult {
	keyword: string;
	instancePath: string;
	schemaPath: string;
	params: Record<string, string | string[]>;
	message?: string;
	}

Steps to Reproduce

import Fastify from "fastify";

const fastify = Fastify({
	schemaErrorFormatter: (errors, dataVar) => {
		const [error] = errors;

		const path = (error.instancePath ?? "")
			.replace("/", ".")
			.replace(/\/(\d)/, "[$1]");

		let { message } = error;
		if (error.keyword === "enum") {
			const values = error.params.allowedValues as string[];
			message += `: ${values.join(", ")}`;
		}

		return new Error(`${dataVar}${path} ${message.replace(/"/g, "'")}`);
	}
});

test.ts:12:13 - error TS2339: Property 'keyword' does not exist on type 'FastifySchemaValidationError'.

12   if (error.keyword === "enum") {
               ~~~~~~~

test.ts:13:25 - error TS2339: Property 'params' does not exist on type 'FastifySchemaValidationError'.

13    const values = error.params.allowedValues as string[];

Workaround:

import Fastify, { ValidationResult } from "fastify";

const fastify = Fastify({
	schemaErrorFormatter: (errors, dataVar) => {
		const [error] = errors as unknown as ValidationResult[];

		const path = (error.instancePath ?? "")
			.replace("/", ".")
			.replace(/\/(\d)/, "[$1]");

		let { message } = error;
		if (error.keyword === "enum") {
			const values = error.params.allowedValues as string[];
			message += `: ${values.join(", ")}`;
		}

		return new Error(`${dataVar}${path} ${message.replace(/"/g, "'")}`);
	}
});_
	

Expected Behavior

Compiles, resulting in pretty errors like this:
body.roles[0] must be equal to one of the allowed values: internal, owner, admin, communicator
body.roles must NOT have more than 1 items
querystring.ownerId must NOT have fewer than 28 characters

[mcollina]

This is somewhat expected as the validation library is configurable. It would be good to implement generics for this.