Next build logs source-map read errors for existing pnpm workspace dependency maps

[ceolinwill]

Link to the code that reproduces this issue

https://github.com/ceolinwill/nextjs-pnpm-sourcemap-error

To Reproduce

1. Start a new nextjs app using pnpm workspaces
2. Add the workflow library
3. Create a workflow using the AI SDK
4. Run pnpm build

Or:

1. Clone this repo
2. Run pnpm build

Current vs. Expected behavior

Current behavior

The build succeeds, but Next logs source-map errors:

ERROR failed to read input source map: failed to find input source map file "index.js.map" in "node_modules/.pnpm/@ai-sdk+provider-utils@5.0.1_zod@4.4.3/node_modules/@ai-sdk/provider-utils/dist/index.js" file as either "node_modules/.pnpm/@ai-sdk+provider-utils@5.0.1_zod@4.4.3/node_modules/@ai-sdk/provider-utils/dist/index.js.map" or with appended .map
    at crates/swc/src/lib.rs:398

ERROR failed to read input source map: failed to find input source map file "index.js.map" in "node_modules/.pnpm/@workflow+serde@4.1.0/node_modules/@workflow/serde/dist/index.js" file as either "node_modules/.pnpm/@workflow+serde@4.1.0/node_modules/@workflow/serde/dist/index.js.map" or with appended .map
    at crates/swc/src/lib.rs:398

The referenced map files do exist:

test -f node_modules/.pnpm/@ai-sdk+provider-utils@5.0.1_zod@4.4.3/node_modules/@ai-sdk/provider-utils/dist/index.js.map
test -f node_modules/.pnpm/@workflow+serde@4.1.0/node_modules/@workflow/serde/dist/index.js.map

Expected behavior

Next should not log source-map read errors when the dependency source map files exist.

Additional context

This reproduces in a pnpm workspace with a Next app under apps/web.

It looks like the source-map path is being resolved relative to the app directory, while pnpm’s virtual store is at the workspace root.

The error appears when workflow/next compiles a workflow step that imports AI SDK packages. A plain Next app importing AI SDK did not reproduce it.

However, I only noticed this issue when I upgraded to the AI SDK v7. It wasn't happening on v6.

Related issues:

• Turbopack: 'failed to read input source map' for node_modules files that have valid source maps next.js#90910
• Failed to read import sourcemap when loading start(flow) in monorepo project #338
• Next build logs source-map read errors for existing pnpm workspace dependency maps next.js#95255

[vladkens]

The loader source-map fix from #2693 landed on main (the 5.0.0-beta line) and is present in the latest 5.0.0-beta.34, but it hasn't been backported to the stable 4.x line. On stable workflow@4.6.0 the warning still reproduces during next build:

ERROR failed to read input source map: failed to find input source map file "index.js.map" in "node_modules/.pnpm/@ai-sdk+provider-utils@5.0.7_zod@4.4.3/node_modules/@ai-sdk/provider-utils/dist/index.js" file as either "node_modules/.pnpm/@ai-sdk+provider-utils@5.0.7_zod@4.4.3/node_modules/@ai-sdk/provider-utils/dist/index.js.map" or with appended .map

Environment:

• Next.js 16.2.10 (Turbopack, next build)
• pnpm workspace monorepo
• withWorkflow from workflow/next, workflow@4.6.0
• @ai-sdk/provider-utils@5.0.7

Verified against the repo: workflow@4.6.0 does not contain the fix commit (24f3707), whereas 5.0.0-beta.34 does.

Could #2693 be backported to a stable 4.x release? Projects that can't move to the 5.0 beta are otherwise stuck with the warning on every build. Thanks!

[NathanColosimo]

Backport merged in #2926 @vladkens ! Should be out with next 4.x release. Let us know if any issues!