nyc generates inconsistent file delimiters

Link to bug demonstration repository

https://github.com/david-kirkland/ng18-code-coverage/tree/bug-nyc-file-paths

Branch = bug-nyc-file-paths

Expected Behavior

The generated coverage JSON has consistent file path delimiters.

Observed Behavior

The generated coverage JSON has inconsistent file path delimiters.

Sometimes it uses a forward slash and sometimes it uses a double backslash. This becomes a problem when attempting to merge reports as coverage is not calculated cumulatively when the file paths do not match between reports.

Troubleshooting steps

You will see in the repo that I am attempting to merge component and e2e test coverage reports (via npm run test:coverage), both generated by Cypress. I am not saying the file path delimiters differ for component and e2e tests. I'm saying the generated JSON coverage will use different file path delimiters for the same file when re-running the same test type (component or e2e) without any other changes. For example, run npm run test:component and sometimes you will get...

Re-run npm run test:component without making any changes and the next time you might get...

Note: I am on a company-issued Windows 10 Enterprise machine.

The bug still occurs when I put cache: false in my nyc config.

Environment Information

  System:
    OS: Windows 10 10.0.19045
    CPU: (12) x64 13th Gen Intel(R) Core(TM) i7-1365U
    Memory: 13.74 GB / 31.64 GB
  Binaries:
    Node: 22.4.1 - ~\AppData\Local\fnm_multishells\11776_1721413704500\node.EXE
    npm: 10.8.1 - ~\AppData\Local\fnm_multishells\11776_1721413704500\npm.CMD
  npmPackages:
    @jsdevtools/coverage-istanbul-loader: 3.0.5 => 3.0.5
    istanbul-lib-coverage: 3.2.2 => 3.2.2
    nyc: 17.0.0 => 17.0.0
    source-map-support: ^0.5.21 => 0.5.21
    ts-node: ^10.9.2 => 10.9.2
    typescript: 5.5.3 => 5.5.3

istanbuljs / nyc