class-validator doesn't appear to do anything in NestJS application

Question

I'm setting up a new NestJS application, and I've just added class-validator in order to validate controller input, but it seems to be completely ignored. This is the DTO:

import {IsString} from 'class-validator';

export class CreateCompanyDto {
    @IsString()
    name: string | undefined;
}

This is the controller:

import {
    Body,
    Controller,
    InternalServerErrorException,
    Post,
    Request,
    UseGuards, ValidationPipe
} from '@nestjs/common';
import * as admin from 'firebase-admin';
import {User} from 'firebase';
import {AuthGuard} from '../auth/auth.guard';
import {CurrentUser} from '../auth/current-user.decorator';
import {CreateCompanyDto} from './dto/create-company.dto';

@Controller('vendor')
export class VendorController {

    @Post()
    @UseGuards(AuthGuard)
    async create(@CurrentUser() user: User, @Request() req: any, @Body(new ValidationPipe({ transform: true })) company: CreateCompanyDto) {
        console.log(JSON.stringify(company));
        throw new InternalServerErrorException('meh?');

         // irrelevant code
    }

}

I would expect the code to throw a validation error and never hit the method itself, but instead it runs into the exception, and the object is logged exactly as it came in.

package.json:

{
    "name": "functions",
    "scripts": {
        "lint": "tslint --project tsconfig.json",
        "prebuild": "(cd src && rm settings.json && ln -s ../configs/prod.json settings.json)",
        "build": "tsc",
        "prebuild:dev": "(cd src && rm settings.json && ln -s ../configs/dev.json settings.json)",
        "build:dev": "tsc",
        "serve": "concurrently \"npm run build:dev -- --watch\" \"firebase emulators:start --only functions\"",
        "shell": "npm run build && firebase functions:shell",
        "start": "npm run shell",
        "deploy": "firebase deploy --only functions",
        "logs": "firebase functions:log"
    },
    "engines": {
        "node": "8"
    },
    "main": "lib/functions/src/index.js",
    "dependencies": {
        "@elastic/elasticsearch": "^7.6.0",
        "@nestjs/common": "^6.11.11",
        "@nestjs/core": "^6.11.11",
        "@nestjs/platform-express": "^6.11.11",
        "@types/airtable": "^0.5.7",
        "@types/nodemailer": "^6.4.0",
        "airtable": "^0.8.1",
        "class-transformer": "^0.2.3",
        "class-validator": "^0.11.0",
        "cors": "^2.8.5",
        "express": "^4.17.1",
        "firebase": "^7.10.0",
        "firebase-admin": "^8.9.2",
        "firebase-functions": "^3.3.0",
        "nodemailer": "^6.4.4",
        "reflect-metadata": "^0.1.13",
        "rxjs": "^6.5.4",
        "slugify": "^1.4.0"
    },
    "devDependencies": {
        "concurrently": "^5.1.0",
        "tslint": "^6.0.0",
        "typescript": "~3.7.5"
    },
    "private": true
}

What am I missing here?

Update I did a little debugging, and I can tell where it's going wrong, even though I still don't know why.

In the ValidationPipe.transform method, it returns the raw input, because metatype is undefined:

    async transform(value, metadata) {
        const { metatype } = metadata;
        if (!metatype || !this.toValidate(metadata)) {
            return value;
        }

        // ...
    }

Answer 1

Ok, the debugging gave me enough info to find the issue on Google, where I found this Github issue: https://github.com/nestjs/nest/issues/690

You need to enable "emitDecoratorMetadata": true in your tsconfig.json file for this to work.