prefer-nextjs-12-minor-performance-milestone

What it flags

Flags workflows that visibly run next build when the repository depends on Next.js 12.0, 12.1, or 12.2.

The rule recommends 12.3.x as the first target because some teams cannot jump major versions immediately, while 12.3 is a meaningful 12.x build-performance and stability milestone.

Why it matters

Next.js 12.x had several CI-relevant minor releases.

• 12.1: on-demand ISR beta, broader SWC compiler support, SWC minification release candidate, image cache improvements, and self-hosting output improvements
• 12.2: on-demand ISR stable, middleware stable, image improvements, SWC plugin work, standalone output stabilization, and smaller helper/runtime output
• 12.3: SWC minifier stable, stable next/future/image, Fast Refresh improvements for config files, and more image/compiler stabilization

For repositories still pinned to early 12.x, moving to 12.3.x can be a smaller compatibility step than a major-version migration while still targeting build-time wins.

Current heuristic

The rule requires both:

• a detectable next dependency in root package.json
• a workflow job that visibly runs next build

It does not flag Next.js 12.3 or newer.

When to ignore it

Ignore this finding when:

• the project is intentionally pinned below 12.3 for compatibility reasons
• the visible workflow job does not represent a meaningful Next.js production build
• the team is already planning a validated major-version migration instead

Suggested verification

• Compare next build wall-clock time before and after the upgrade
• Check minification time, generated JavaScript size, and image-related build warnings separately when logs make that visible
• Keep the change only if the runtime gain and compatibility profile are acceptable

Sources

• https://nextjs.org/blog/next-12-1
• https://nextjs.org/blog/next-12-2
• https://nextjs.org/blog/next-12-3