Hi!

I encountered the following strange error when trying to set up a build step with tsup for a library in a monorepo:

$ pnpm nx build my-library # <-- original command run in terminal

   ✔    1/1 dependent project tasks succeeded [1 read from cache]

   Hint: you can run the command with --verbose to see the full dependent project outputs

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> nx run my-library:build

> @my-monorepo/[email protected] build /my-monorepo/libs/my-library
> tsup
▲ [WARNING] "tsconfig.json" does not affect esbuild's own target setting [tsconfig.json]
    ../../tsconfig.base.json:11:8:
      11 │         "target": "es2015",
         ╵         ~~~~~~~~
  This is because esbuild supports reading from multiple "tsconfig.json" files within a single build, and using different language targets for different files in the same build wouldn't be correct. If you want to set esbuild's language target, you should use esbuild's own global "target" setting such as with "target: 'es2015'".
▲ [WARNING] "tsconfig.json" does not affect esbuild's own target setting [tsconfig.json]
    ../../tsconfig.base.json:11:8:
      11 │         "target": "es2015",
         ╵         ~~~~~~~~
  This is because esbuild supports reading from multiple "tsconfig.json" files within a single build, and using different language targets for different files in the same build wouldn't be correct. If you want to set esbuild's language target, you should use esbuild's own global "target" setting such as with "target: 'es2015'".
CLI Building entry: src/index.ts
CLI Using tsconfig: tsconfig.json
CLI tsup v7.0.0
CLI Using tsup config: /my-monorepo/libs/my-library/tsup.config.ts
CLI Target: es2015
CLI Cleaning output folder
ESM Build start
ESM ../../dist/libs/my-library/index.js 13.21 KB
ESM ⚡️ Build success in 111ms
onSuccess:
  - Copied README.md and ../../LICENSE to out directory.
  - Merged package.json and ../../package.json and wrote to out directory.
  - Done.
DTS Build start
src/index.ts(1,15): error TS6059: File '/my-monorepo/libs/my-other-library/src/index.ts' is not under 'rootDir' '.'. 'rootDir' is expected to contain all source files.
  The file is in the program because:
    Imported via "@my-monorepo/my-other-library" from file '/my-monorepo/libs/my-library/src/index.ts'
Error: error occured in dts build
    at Worker.<anonymous> (/my-monorepo/node_modules/.pnpm/[email protected]_@[email protected][email protected][email protected][email protected]/node_modules/tsup/dist/index.js:2297:26)
    at Worker.emit (node:events:513:28)
    at MessagePort.<anonymous> (node:internal/worker:243:53)
    at [nodejs.internal.kHybridDispatch] (node:internal/event_target:737:20)
    at exports.emitMessage (node:internal/per_context/messageport:23:28)
DTS Build error
RollupError: Failed to compile. Check the logs above.
    at error (/my-monorepo/node_modules/.pnpm/[email protected]/node_modules/rollup/dist/shared/rollup.js:279:30)
    at Object.error (/my-monorepo/node_modules/.pnpm/[email protected]/node_modules/rollup/dist/shared/rollup.js:24825:20)
    at Object.error (/my-monorepo/node_modules/.pnpm/[email protected]/node_modules/rollup/dist/shared/rollup.js:24019:42)
    at generateDtsFromTs (/my-monorepo/node_modules/.pnpm/[email protected]_@[email protected][email protected][email protected][email protected]/node_modules/tsup/dist/rollup.js:7498:22)
    at /my-monorepo/node_modules/.pnpm/[email protected]_@[email protected][email protected][email protected][email protected]/node_modules/tsup/dist/rollup.js:7505:59
    at _nullishCoalesce (/my-monorepo/node_modules/.pnpm/[email protected]_@[email protected][email protected][email protected][email protected]/node_modules/tsup/dist/rollup.js:1:198)
    at Object.transform (/my-monorepo/node_modules/.pnpm/[email protected]_@[email protected][email protected][email protected][email protected]/node_modules/tsup/dist/rollup.js:7505:18)
    at /my-monorepo/node_modules/.pnpm/[email protected]/node_modules/rollup/dist/shared/rollup.js:25024:40
 ELIFECYCLE  Command failed with exit code 1.

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 >  NX   Ran target build for project my-library and 1 task(s) they depend on (4s)
 
    ✖    1/2 failed
    ✔    1/2 succeeded [1 read from cache]

It's a Nx monorepo and my-library depends on my-other-library.

Directory structure looks like following:

my-monorepo/
├─ libs/
│  ├─ my-library/
│  │  ├─ tsconfig.json
│  │  ├─ tsup.config.ts
│  ├─ my-other-library/
│  │  ├─ tsconfig.json
├─ tsconfig.base.json

In tsconfig.base.json:

{
    "compilerOptions": {
        "rootDir": ".",
        "paths": {
            "@my-monorepo/my-library": [
                "libs/my-library/src/index.ts"
            ],
            "@my-monorepo/my-other-library": [
                "libs/my-other-library/src/index.ts"
            ],
        }
    }
}

In libs/my-library/tsconfig.json:

{
    "extends": "../../tsconfig.base.json"
}

My theory is that the issue has to do with tsup (or rollup-plugin-dts, which it uses internally for generating the declaration files) viewing "rootDir": "." as pointing to /my-monorepo/libs/my-library/ (the root directory of the library), when in fact "rootDir": "." is meant to be viewed as pointing to /my-monorepo/ (the root directory of the monorepo) as it's defined in tsconfig.base.json which resides in the root directory of the monorepo, so relative paths within that file should be resolved relative to the location of the file.