Turbopack: Add filesize condition for loader rules

[vitalets]

Goals

• Enable Turbopack loaders to conditionally apply based on file size.
• Provide a simpler and clearer alternative to using RegExp with the content rule for size-based conditions.
• Allow size-based conditions to work for binary files (e.g., PNG, JPG), which cannot be matched using the current content rule.
• Offer functionality similar to Webpack’s url-loader limit option.

Non-Goals

No response

Background

Next.js 16 introduced Turbopack condition rules, which allow loaders to apply only to files matching specific criteria. There are already path and content rules, which are very useful.

It would be great to have an additional rule for file size. This would allow developers to apply a loader only to files whose size is smaller (or greater) than a provided limit. The idea is similar to Webpack’s url-loader limit option.

Alternative

For text-based files, this can be achieved using the existing content rule, which accepts a RegExp.
For example, to inline SVG images smaller than 4 KB, I can use the following config:

const nextConfig = {
  turbopack: {
    rules: {
      '*.svg': {
        loaders: ['turbopack-inline-svg-loader'],
        condition: {
          content: /^[\s\S]{0,4000}$/, // <-- Inline SVGs smaller than ~4 KB
        },
        as: '*.js',
      },
    },
  },
};

While this works for textual files, it fails for binary ones (e.g., *.png):

failed to convert rope into string
Caused by:
- invalid utf-8 sequence of 1 bytes from index 0

Also, relying on RegExp for this is not as straightforward as having a dedicated option for file size.

Proposal

Add a new condition limit specifying the maximum size of a file (in bytes) to apply a loader:

const nextConfig = {
  turbopack: {
    rules: {
      '*.svg': {
        loaders: ['turbopack-inline-svg-loader'],
        condition: {
          limit: 4096 // <-- Inline SVGs smaller than ~4Kb
        },
        as: '*.js',
      },
    },
  },
};