Treat build warnings as errors

[Asaf-S]

Goals

1. Help developers who want it to avoid missing out on warnings.
2. Help team leaders who want to ensure a certain level of attention to details from their developers, without having to read the build log.

Non-Goals

1. Change the default behavior

Background

I accidentally read the build log in our server after a while, and saw a few warnings as the one listed below:

For production Image Optimization with Next.js, the optional 'sharp' package is strongly recommended. Run 'npm i sharp', and Next.js will use it automatically for Image Optimization.

I want a way to force my team to avoid missing out on warnings.

I saw #29129, and his last comment:

It would be nice I suppose to optionally elevate next build warnings as errors via something like a --strict flag

and couldn't agree more.

Proposal

add --treatWarningsAsErrors flag to treat warnings as errors