[api-extractor] dts can not rollup when `mainEntryPointFilePath` in `node_modules` folder

[Timeless0911]

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Summary

When using dtsRollup feature, I found that it is unable to bundle types from mainEntryPointFilePath in node_modules folder.

Repro steps

https://github.com/Timeless0911/api-extractor-issue-node-modules-entry

Run pnpm gen-types to repro this issue.

Expected result:

If I configure mainEntryPointFilePath to "<projectFolder>/dist/index.d.ts",, the dts bundle in untrimmedFilePath is:

// dist-types/index.d.ts
export declare const num1 = 1;

export declare const num2 = 2;

export declare const num3 = 3;

export declare const numSum: number;

export declare const str1 = "str1";

export declare const str2 = "str2";

export declare const str3 = "str3";

export declare const strSum: string;

export { }

Actual result:

In repro demo, I copy the dist folder generated by tsc to node_modules/.temp

When mainEntryPointFilePath set to "mainEntryPointFilePath": "<projectFolder>/node_modules/.temp/index.d.ts",, the dts bundle in untrimmedFilePath is:

// dist-types/index.d.ts

export * from "./sum";
export * from "./utils/numbers";
export * from "./utils/strings";

export { }

Details

I want to use the dtsRollup feature to bundle the dts files emitted by tsc, so I need to put them in a temporary folder of node_modules to avoid publishing them to npm.

I do not want to put them directly in temp folder in projectFolder since most build tools like swc and webpack all generate temp files in node_modules folder.

Standard questions

Please answer these questions to help us investigate your issue more quickly:

Question	Answer
@microsoft/api-extractor version?	7.48.1
Operating system?	Mac
API Extractor scenario?	rollups (.d.ts)
Would you consider contributing a PR?	No
TypeScript compiler version?	5.7.2
Node.js version (node -v)?	22.10.0