PR #91882: fix(jest): include loaderFile in imageConfig and moduleNameMapper for custom image loaders

• Repository: vercel/next.js
• Author: sleitor
• State: open | merged: False
• Link: https://github.com/vercel/next.js/pull/91882

Description (problem / solution / changelog)

What?

When next.config.js configures a custom image loader via images.loaderFile, Jest tests fail with:

Image with src "/images/test.jpg" is missing "loader" prop.

Why?

The imageConfig object built in packages/next/src/build/jest/jest.ts (added in #89536) includes loader but not loaderFile. This causes two problems:

1. process.env.__NEXT_IMAGE_OPTS (injected by the SWC transformer) does not contain loaderFile, so the image config is incomplete.
2. The moduleNameMapper does not redirect next/dist/shared/lib/image-loader to the custom file, unlike what webpack does via create-compiler-aliases.ts in production.

When config.loader === 'custom' but no custom loader module is wired up, get-img-props.ts throws the "missing loader prop" error.

How?

1. Added loaderFile to the imageConfig object so it is included in __NEXT_IMAGE_OPTS.
2. Added moduleNameMapper entries for next/dist/shared/lib/image-loader and next/dist/esm/shared/lib/image-loader pointing to nextConfig.images.loaderFile when set — mirroring what create-compiler-aliases.ts does for webpack.

Fixes #91876

Changed files

• packages/next/src/build/jest/jest.ts (modified, +12/-0)

PR #91884: fix(next/jest): respect images.loaderFile config in Jest tests

• Repository: vercel/next.js
• Author: Krishnachaitanyakc
• State: open | merged: False
• Link: https://github.com/vercel/next.js/pull/91884

Description (problem / solution / changelog)

Summary

Fixes #91876

When images.loaderFile is configured in next.config.js, webpack and Turbopack alias the default image loader (next/dist/shared/lib/image-loader) to the user's custom loader file at build time. However, the next/jest configuration did not set up a corresponding moduleNameMapper entry, so the default image loader (which carries __next_img_default = true) was always imported during Jest tests.

Combined with the image config reporting loader: 'custom', this caused next/image to throw:

Image with src "..." is missing "loader" prop.

Changes

• packages/next/src/build/jest/jest.ts: Added a moduleNameMapper entry that aliases next/dist/shared/lib/image-loader to the user's loaderFile when configured, mirroring the webpack/turbopack alias in create-compiler-aliases.ts.
• test/production/app-dir/image-jest-custom-loader/: Added a test that verifies next/image works correctly in Jest when a custom loaderFile is configured.

How it works

The root cause is that get-img-props.ts checks '__next_img_default' in loader (line 352) alongside config.loader === 'custom' (line 355). During builds, the loaderFile alias replaces the default loader import with the user's custom loader (which lacks the __next_img_default marker), so the check passes. In Jest, this alias was missing, so the default loader was always used while the config still said loader: 'custom', triggering the error.

Test plan

• New test test/production/app-dir/image-jest-custom-loader/image-jest-custom-loader.test.ts validates that next/image renders successfully in a Jest environment with a custom loaderFile configured
• Existing test test/production/app-dir/image-jest-qualities/ continues to pass (no regression for non-custom-loader setups)

Changed files

• packages/next/src/build/jest/jest.ts (modified, +10/-0)
• test/production/app-dir/image-jest-custom-loader/app/app/page.tsx (added, +8/-0)
• test/production/app-dir/image-jest-custom-loader/image-jest-custom-loader.test.ts (added, +105/-0)